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diff --git a/77630-0.txt b/77630-0.txt new file mode 100644 index 0000000..6ecd9f1 --- /dev/null +++ b/77630-0.txt @@ -0,0 +1,5288 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 77630 *** + + + + + TRANSCRIBER’S NOTE + + Italic text is denoted by _underscores_. + + Some minor changes to the text are noted at the end of the book. + + + + + AN + + ESSAY + + ON + + _COMBUSTION_, + + WITH A VIEW TO A + + NEW ART + + OF + + DYING AND PAINTING. + + WHEREIN + + THE PHLOGISTIC AND ANTIPHLOGISTIC HYPOTHESES + ARE PROVED ERRONEOUS. + + + BY MRS. FULHAME. + + + LONDON: + + PRINTED FOR THE AUTHOR, + + BY J. COOPER, BOW STREET, COVENT GARDEN, + + And Sold by J. JOHNSON, No. 72, St. Paul’s Church Yard; + G. G. and J. ROBINSON, Paternoster Row; and + T. CADELL, Jun. and W. DAVIES, Strand. + + 1794. + + [ENTERED AT STATIONERS HALL.] + + + + +PREFACE. + + +The possibility of making cloths of gold, silver, and other metals, by +chymical processes, occurred to me in the year 1780: the project being +mentioned to Doctor Fulhame, and some friends, was deemed improbable. +However, after some time, I had the satisfaction of realizing the idea, +in some degree, by experiment. + +Animated by this small success, I have, from time to time, ever since, +prosecuted the subject as far as pecuniary circumstances would permit. + +I imagined in the beginning, that a few experiments would determine the +problem; but experience soon convinced me, that a very great number +indeed were necessary, before such an art could be brought to any +tolerable degree of perfection. + +A narration of the numerous experiments, which I made with this view, +would far exceed the bounds, I prescribe myself in this essay; I shall +therefore present the reader only with a few, selecting such as I judge +most interesting, and best adapted to illustrate the subject. + +Though I was, after some considerable time, able to make small bits of +cloth of gold, and silver, yet I did not think them worthy of public +attention; but by persevering, I at length succeeded in making pieces +of gold cloth, as large as my finances would admit. + +Some time after this period, I found the invention was applicable +to painting, and would also contribute to facilitate the study of +geography: for I have applied it to some maps, the rivers of which I +represented in silver, and the cities in gold. The rivers appearing, as +it were, in silver streams, have a most pleasing effect on the sight, +and relieve the eye of that painful search for the course, and origin, +of rivers, the minutest branches of which can be splendidly represented +in this way. + +Notwithstanding this further success, I was dubious about the propriety +of publishing this Essay; I therefore shewed some specimens of these +metallic stuffs to persons, whom I thought qualified to judge of them: +some approved of them very much, and were pleased to say, that the +invention would make an era in the arts; others thought it a pretty +conceit; and others were of opinion, that the stuffs had not that +splendour, or burnished appearance, which could entitle them to public +notice. + +The latter opinion had much weight with me; for it must be allowed, +that the specimens, which I shewed them, had not that lustre and +polish, necessary for shoulder-knots, lace, spangles, gold muslins, +&c.; that some of them had a reddish cast, bordering on the colour of +copper, some a purple, mixed with gold; and that some of them were +unequal in the die, and seemed stained; which imperfections were owing +to a partial reduction of the metal in the fibres of the silk. + +But all these imperfections, except the want of that burnished lustre +so necessary for gold lace, spangles, &c. I knew I could remedy; and +therefore the criticism, as far as it relates to them, had no great +influence with me. + +I am in possession of some pieces, one of which is about a yard in +length, which have scarce any of these imperfections. + +Moreover, that high polish of burnished gold, so necessary in spangles, +lace, &c., would, in my opinion, be a great imperfection in gold stuffs +designed for whole suits; as a person in such a habit, would look like +a gilded statue. + +I saw a piece of gold stuff made for the late King of Spain, which was +of a purple colour, with gold wire shining through it, though rather +obscurely; and it was much admired: I was so struck with its beauty, +that I attempted to imitate it on a small bit of white silk; and +succeeded, having produced a beautiful purple colour, with gold beaming +through it. + +Therefore, the want of that burnished appearance is no objection to +this art; for the paler, and cooler, to a certain degree, the colour of +the gold is, the more lovely do these metallic cloths appear. + +I made small bits of gold tiffany, which looked exceedingly beautiful; +the fineness of the thread contributing much to that effect; and, in my +opinion, such webs are inimitable by mechanical means. + +Beside, though I am not able to make cloths like burnished gold, others +of greater means and abilities may; for we cannot pretend to prescribe +any limits to the perfection, at which chymistry, and the arts, may +arrive. + +However, I must acknowledge, that this unfavourable judgement suspended +my intention of publishing this little work, until a celebrated +philosopher happening, some time in October 1793, to see some of the +same pieces, and indeed, some of the worst, viewed the performance in a +very different light. + +This illustrious friend of science not only approved of the specimens +shewn him, but offered to have a memoir on the subject presented to the +Royal Society: but different incidents dissuaded me from that mode of +publication, and induced me to adopt the present. + +I now no longer hesitated about the propriety of publishing; for, +every thing considered, I judged, that though this art could never +be established, which is by no means my opinion, yet the experiments +themselves, upon which I attempted to found it, as they are new, and +seem to throw some light on the theory of combustion, are not unworthy +the attention of Chymists. + +Those who viewed my performance with a favourable eye, were of opinion, +that I should dedicate this Essay to some patron of the arts; or +apply for his Majesty’s Royal letters patent, in order to reimburse +the expence necessarily incurred in this investigation, an expence so +disproportionate to the fortune which supported it, that nothing but a +certain fatality, and the hope of reward, could induce me to persevere. + +As to patrons, I have heard of such beings on the record of fame; but +never saw one: on the contrary, it has been my lot to know of many, +whose malignant breath, as far as its deadly influence can extend, +never ceases to blast the unsheltered blossoms of science.—And as for a +patent, had I even the means, I should perhaps never attempt it; for if +we may judge of the future by the past, I can safely affirm, that such +an application would be vain. + +Thus circumstanced, I publish this Essay in its present imperfect +state, in order to prevent the furacious attempts of the prowling +plagiary, and the insidious pretender to chymistry, from arrogating to +themselves, and assuming my invention, in plundering silence: for there +are those, who, if they can not by chymical, never fail by stratagem, +and mechanical means, to deprive industry of the fruits, and fame, of +her labours. + +But the British empire should not forget, that she owes her power and +greatness to commerce; that she is, as it were, the hive of the arts, +and should not, by the sulphureous vapour of oppression, and neglect, +compel her bees to swarm for protection to foreign climes, but rather +permit them to roam in their native soil, and allow them, in the winter +of life, to sip a little of the honey of their own industry. + +The nation, whose evil genius withholds this protection, only sounds +the trumpet of emigration; and must erelong lament her cities deserted, +her fields brown with desolation, and herself the easy prey, and vile +drudge of surrounding greatness. + +I first imagined, that the proper title of this performance, should +be, an Essay on the Art of making Cloths of Gold, Silver, and other +Metals, by chymical processes; but reflecting on the imperfect state +of the art, and that my experiments related not only to the reduction, +but also to the calcination of metals, and other combustible bodies, I +determined to entitle it, An Essay on Combustion, with a view to a new +Art of Dying and Painting, which includes every thing the experiments +can extend to. + +As to the style, I have endeavoured to relate the experiments in a +plain and simple manner, aiming more at perspicuity, than elegance. + +I have adopted the French Nomenclature, as the terms of it are so +framed, as to prevent circumlocution, assist the memory, by pointing +out the combination, and state of the elements existing in each +compound, as far as they are known; advantages to be found in no other +Nomenclature. + +However, the English reader must regret, that the French chymists have +not preferred the terms _air_, and _ammonia_, to the less harmonious +sounds, _gas_, and _ammoniac_. I took the liberty of writing the latter +_ammonia_. + +I have not related my experiments in the order, in which they were +made, sensible that such a narration would be tedious, and that a short +extract from them would answer every purpose at present intended. + +The experiments related I have endeavoured to arrange in such a manner, +as mutually to illustrate each other, by contrasting the successful +with those, that failed, thus pointing out a general principle, which +forms a chain through the whole, connects all the experiments, shows +their points of coincidence, and disagreement, and by this means +furnishes us with _data_, by which, I hope, the art may be improved. + +This arrangement also facilitates the perusal, and relieves the mind +of that fatiguing attention, which must necessarily be given to an +indigested mass of insulated experiments, that have no clew to connect +them, but has, on the other hand, its disadvantages; for it throws a +sameness on the work, incompatible with that variety which is often so +agreeable. + +My apparatus consisted chiefly of a few glass vessels for the solution +of metals, and the formation of such elastic fluids, as I used. The +cheapest, and the most simple of those described by Dr. Priestley +answered my purpose. + +Dr. Nooth’s machine for combining carbonic acid with water, is very +convenient for making small experiments with some kinds of gas; as the +base of that machine serves to contain the materials, from which the +gas is obtained; and the middle glass the cloth previously dipped in +the metallic solution, on which the experiment is to be made. + +The cloth may be suspended in this part of the machine, by means of a +thread, and a cork. + +As this machine is useful only in experiments on a very small scale, I +sometimes used tall glass cylinders, in which I suspended the subject +of the experiment, by means of a thread, a cork, and a bit of cement. + +This cylinder I placed over a vessel containing the materials, which +produced the gas. + +It is very convenient to have cylinders of different sizes, +proportioned to the scale, on which the experiments are to be made. + +But machinery for confining elastic fluids is not always necessary; as +most of the experiments may be performed in the open air. + +It may appear presuming to _some_, that I should engage in pursuits of +this nature, but averse from indolence, and having much leisure, my +mind led me to this mode of amusement, which I found entertaining, and +will, I hope, be thought inoffensive by the liberal, and the learned. +But censure is perhaps inevitable; for some are so ignorant, that they +grow sullen and silent, and are chilled with horror at the sight of any +thing, that bears the semblance of learning, in whatever shape it may +appear; and should the _spectre_ appear in the shape of _woman_, the +pangs, which they suffer, are truly dismal. + +There are others, who suffer the same torture in a still higher degree; +but by virtue of an _old inspiring tripod_, on which ignorance, +servility, or chance, has placed them, assume a dictatorship in +science, and fancying their rights and prerogatives invaded, swell with +rage, and are suddenly seized with a violent and irresistible desire +of revenge, manifesting itself by innuendos, nods, whispers, sneers, +grins, grimace, satanic smiles, and witticisms uttered sometimes in +the acute, and sometimes in the nasal obtuse twang, with an affected +hauteur, and contempt of the _spectre_; shrugs, and a variety of other +contortions, attending. + +Sometimes the goblin, which thus agitates them, lurks latent, and +nothing is perceived but hollow murmurs, portending storms: sometimes +the lurking fiend darts with sidelong fury at the devoted object, +which, if unarmed, falls a victim to the grisly monster. + +But happily for human kind, the _magic tripod_ drags none into its +dizzy vortex, but those who are radically stupid, and malicious, who +are the beasts of prey destined to hunt down unprotected genius, to +stain the page of biography, or to rot unnoted in the grave of oblivion. + +Although the surge of deliberate malice be unavoidable, its force is +often spent in froth, and bubbles; for this little bark of mine has +weathered out full many a storm, and stemmed the boisterous tide; and +though the cargo be not rich, the dangers, which may hereafter be +pourtrayed on _votive tablet_, may serve as a beacon to future mariners. + +But happen what may, I hope I shall never experience such desertion of +mind, as not to hold the helm with becoming fortitude against the storm +raised by ignorance, petulant arrogance, and privileged dulness. + +However, were I not encouraged by the judgement of some friends, and +possessed of specimens, to show the progress made in the art, I should +never perhaps venture to publish this Essay; as I am sensible, it +labours under many imperfections, which inaccuracy of observation, and +the drapery of imagination, must spread over the whole, imperfections +perhaps unavoidable in such a discussion. + +Finding, the experiments could not be explained on any theory hitherto +advanced, I was led to form an opinion different from that of M. +Lavoisier, and other great names. Persuaded that we are not to be +deterred from the investigation of truth by any authority however +great, and that every opinion must stand or fall by its own merits, +I venture with diffidence to offer mine to the world, willing to +relinquish it, as soon as a more rational appears. + + November 5th, 1794. + + + + + CONTENTS. + + + Introduction 1 + + Chap. I. Reduction of Metals by Hydrogen Gas 13 + + ---- II. ------------------- Phosphorus 41 + + ---- III. ------------------- Sulphur 69 + + ---- IV. ------------------- Alkaline Sulphure 84 + + ---- V. ------------------- Sulphurated Hydrogen + Gas 99 + + ---- VI. ------------------- Phosphorated Hydrogen + Gas 113 + + ---- VII. ------------------- Charcoal 124 + + ---- VIII. ------------------- Light 142 + + ---- IX. ------------------- Acids 155 + + ---- X. Oxygenation of Combustible Bodies 161 + + -------------- Azote ibid. + + -------------- Hydrogen 164 + + -------------- Phosphorus 165 + + -------------- Sulphur 166 + + -------------- Charcoal ibid. + + -------------- Metals 169 + + -------------- Light 168, 169 + + ---- XI. Conclusion 178 + + Nomenclature 181 + + + + +INTRODUCTION. + + +Though some of the phenomena of combustion were known from the earliest +ages, yet no rational attempt to explain them was made till about the +middle of the 17th century. + +Before that period, it was supposed by alchymists and physicians, that +sulphur was the inflammable principle, on which all the phenomena of +combustion depended. + +But Beecher perceiving, that sulphur did not exist in several +combustible bodies, asserted it was not the principle of +inflammability; which, he maintained, was a different substance, common +to sulphur and other combustible bodies: this principle he supposed to +be of a dry nature, and called it inflammable Earth. + +Stahl refined this hypothesis by supposing the inflammable earth of +Beccher to be pure fire, fixed in combustible bodies, and constituting +an essential part of them. + +According to Stahl, a combustible body is a compound, containing fixed +fire, or _phlogiston_; and combustion is the disengagement of this +phlogiston from a fixed to a free state, attended sometimes with heat +and light: when these phenomena cease, the body becomes incombustible; +if this calcined body be now heated with charcoal, or any other +inflammable substance, capable of giving it phlogiston, or fixed fire, +it returns again to the class of inflammable bodies. + +This hypothesis is so simple and plausible, that, since the year 1736, +it was received, though differently modified, all over Europe. + +The principal objections to it are, that the existence of phlogiston +cannot be demonstrated; and that it does not explain, why bodies become +heavier after oxygenation, and lighter after reduction. + +M. Lavoisier discovering, that the increase of weight, which bodies +acquire during combustion, is equal to the weight of the combustible +substance, and that of the vital air employed, denied the existence +of phlogiston, or fixed fire, in combustible bodies; though he grants +the existence of combined _caloric_ in them. He seems then to allow +the existence of phlogiston, but to have changed its name to that of +_caloric_, and denied it the power of producing combustion. + +However, after discovering that the increase of weight, which bodies +acquire during combustion, depended on the quantity of the air +absorbed, he was led to the following beautiful hypothesis, equally +simple as that of Stahl; and if ever any hypothesis deserved the name +of theory, surely it is that of M. Lavoisier. + +According to M. Lavoisier, “an inflammable body is nothing else but +a body which has the property of decomposing vital air, and taking +the base from caloric and light; that is to say, the oxygene, which +was united to them; and that a body ceases to be combustible when its +affinity for the oxygene is satisfied, or when it is saturated with +that principle; but that it becomes again combustible, when the oxygene +has been taken from it by another body, which has a stronger affinity +with that principle. + +“When this decomposition of the air is rapid, and, as it were, +instantaneous, there is an appearance of flame, heat, and light; when, +on the contrary, the decomposition is very slow, and quietly made, the +heat and light are scarcely perceptible[1].” + +Thus all the phenomena of oxygenation, which Stahl ascribed to the +disengagement of phlogiston, M. Lavoisier ascribes to the union of +oxygen with combustible bodies. + +And, on the other hand, all the phenomena of reduction, which Stahl +attributed to the union of phlogiston to calcined bodies, M. Lavoisier +attributes to the separation of oxygen from the same. Combustion, +then, according to Stahl, is the transition of phlogiston from one +body to another; and, according to M. Lavoisier, ’tis nothing but the +transition of oxygen from one substance to another. + +Stahl supposed, that the heat, and light, attending combustion proceed +from the burning body; but M. Lavoisier supposes, that the heat, and +light, proceed principally, and almost entirely, from the vital air. + +However, this opinion of M. Lavoisier is far from being established; +for Doctor Crawford has shown, that inflammable air contains a much +greater quantity of heat, than vital air does. + +It is evident, then, that the great advantage, which M. Lavoisier’s +hypothesis has over that of Stahl is, that the former seems to account +for the increase and decrease of weight, which bodies suffer during +calcination, and reduction. + +Notwithstanding this brilliant discovery, which seems to account, with +such ease, for the increase of weight, that bodies acquire during +combustion, M. Macquer was of opinion, that M. Lavoisier’s hypothesis +was insufficient to explode that of Stahl, and endeavoured to remove +the objection urged against the nonexistence of phlogiston, by +supposing it to be light; and that in every case of combustion, light, +and vital air, mutually precipitate each other: so that, according +to M. Macquer, when a body is oxygenated, vital air unites to it, and +disengages light; and, on the other hand, when an oxygenated substance +is reduced to its inflammable state, light unites to it, and disengages +vital air. + +M. Scheele also modified the hypothesis of Stahl, by supposing that +heat, light, and inflammable air, were compounds of empyreal, or vital +air, and phlogiston. Light, he thought, contained more phlogiston than +heat did; and inflammable air more than either: he farther supposed, +that these compounds of vital air and phlogiston were convertible +into one another, by the addition, or subtraction, of phlogiston; and +that, when a metal was reduced by them, they were decomposed; their +phlogiston uniting to the substance reduced. + +His idea of calcination is, that metals either attract empyreal air by +means of their phlogiston, and thus form heat, or that they communicate +their phlogiston to the air, and attract heat from the fire; and that, +either way, there is empyreal air in the calces, which makes the +overplus of their weight[2]. + +The last modification of Stahl’s hypothesis is that of M. Kirwan, who +supposes that inflammable air exists in a fixed, or concrete, state +in all combustible bodies, and is the true phlogiston of the antient +chymists; and, as it can be exhibited in the form of air, its existence +is no longer doubtful. + +M. Kirwan supposes, that, when combustible bodies are calcined, or +changed into acids, they combine most commonly with fixed air, formed +during the operation, by the union of their phlogiston to vital air; +and sometimes to other substances, and water, which is either absorbed +_in specie_, or formed by the union of their phlogiston to vital air, +during calcination. + +He supposes, that some of these are restored to their combustible +state by the decomposition of their fixed air; some partly by the +decomposition of their fixed air, and partly by its expulsion, and +that of the other foreign bodies, they had absorbed; and lastly, that +some recover their combustibility by the expulsion of water, and +others possibly by its decomposition in high degrees of heat. In all +these reductions he supposes a simultaneous reunion of these bodies to +phlogiston, or the inflammable principle[3]. + +Though M. Kirwan’s hypothesis seems to account for the increase +of weight, which bodies acquire during combustion, yet he has not +proved the existence of inflammable air, in a concrete state, in all +combustible bodies; nor has he shown, that fixed air is a compound of +inflammable, and vital air; neither has he proved, that fixed air is +the acidifying principle. + +All these objections have been made, with great justice, to his +hypothesis, by the antiphlogistians; who also object, that M. Kirwan’s +account of calcination, and reduction, is complex, and repugnant to the +simplicity of nature; “for,” says M. De Fourcroy, “as the author had +admitted three general species of calcination, it was necessary, that +he should, likewise, admit three kinds of reduction[4].” + +This criticism is very just; but it will appear, that the +antiphlogistic account of calcination, and reduction, is no less +complex, erroneous, and repugnant to the simplicity of nature: for when +we consider the various sources, whence they derive the oxygen, which +oxygenates bodies; and the long list of metallic reducers, which they +suppose; it must be allowed, that if simplicity be a recommendation, +their hypothesis is destitute of that advantage. + +Thus, according to M. Lavoisier, the oxygen, which oxygenates +combustible bodies, is sometimes derived from vital air; sometimes +from atmospheric air; sometimes from acids; sometimes from water; and +sometimes from metallic oxids, &c. + +On the other hand, the catalogue of substances, which reduce bodies to +their combustible state, is no less numerous. + +“Heat,” says M. De Fourcroy, “separates oxygene from some; one metal +takes it from another; hydrogene, or inflammable gas, takes it from +most metals; and carbone perhaps from all[5].” + +To this list, may be added phosphorus, sulphur, and compounds of these +with hydrogen; also light, and the electric fluid, &c., as will appear +in the sequel. + +But, I shall endeavour to show, that the hydrogen of water is the only +substance, that restores oxygenated bodies to their combustible state; +and that water is the only source of the oxygen, which oxygenates +combustible bodies. + +Want of simplicity is not the only defect in Mr. Lavoisier’s +hypothesis: for he supposes, that the increase of weight, which bodies +acquire during combustion, depends on the absorption of the oxygenous +principle alone. + +Thus, when a bit of phosphorus, sulphur, or charcoal, is burnt in vital +air; the increase of weight, which these bodies acquire, he attributes +entirely to oxygen, or the base of vital air. + +These combustions he explains, by supposing, that the phosphorus, +sulphur, and charcoal, decompose oxygen gas, by absorbing its base +from caloric, and light, which are set free. + +“There is,” says M. Lavoisier, “a total absorption of vital air, or +rather of the oxygene, which forms its base in the combustion of +phosphorus, and the weight of the phosphoric acid obtained, is found to +be rigorously equal to the weight of the phosphorus, added to that of +the vital air employed in its combustion. The same agreement of weights +is observed in the combustion of inflammable gas and vital air, in the +combustion of charcoal[6]”, &c. + +His idea of the calcination of metals is the same. + +“We do not,” says M. Lavoisier, “affirm that vital air combines with +metals to form metallic calces, because this manner of enunciating +would not be sufficiently accurate: but we say, when a metal is heated +to a certain temperature, and when its particles are separated from +each other to a certain distance by heat, and their attraction to each +other is sufficiently diminished, it becomes capable of decomposing +vital air, from which it seizes the base, namely oxygene, and sets the +other principle, namely caloric, at liberty. + +“This explanation of what passes during the calcination is not an +hypothesis, but the result of facts. It is upwards of twelve years, +since the proofs have been laid by one of us, before the eyes of the +academy, and have been verified by a numerous commission. It was then +established, that when the calcination of metals is effected beneath +an inverted glass vessel, or in closed vessels containing known +quantities of air, the air itself is decomposed, and the weight of the +metal becomes augmented by a quantity accurately equal to that of the +air absorbed. It has since been found, that when the operation was +performed in very pure vital air, the whole might be absorbed.” + +“No supposition enters into these explanations; the whole is proved by +weight and measure[7].” + +Hence it is evident, that M. Lavoisier confounds oxygen with oxygen +gas; and considers the latter as a compound of oxygen, light, and +caloric. + +But since the dryest oxygen gas contains a large proportion of water, +as Dr. Priestley and M. Kirwan have shown[8]; and since the whole of +the gas, except the caloric, and light, is absorbed, it necessarily +follows, that the increase of weight, which bodies acquire during +combustion, depends not only on the oxygen, but also on the water, +contained in vital air. + +Therefore oxids are compounds of combustible bodies united to oxygen, +and water. + +Another great objection to M. Lavoisier’s hypothesis, is, that he +supposes both oxygenation, and reduction, effected by a single affinity. + +Thus, according to him, when iron reduces a sulphate of copper, the +iron does nothing more, than separate the oxygen from the copper, by +its superior attraction for that principle. + +From this view of combustion, grounded on the most accurate experiments +in chymistry, it is manifest, that the antiphlogistic hypothesis does +not account fully for the increase of weight, which bodies acquire +during combustion; and consequently, that it cannot be admitted as a +just theory. + + + + +CHAPTER I. + +REDUCTION OF METALS + +BY + +HYDROGEN GAS. + + +As Hydrogen, or the base of inflammable air, seems to act an important +part in the following experiments, and is, according to some chymists, +pure phlogiston itself; I have therefore assigned the first chapter in +this essay to hydrogen gas, this being the most simple form, in which +hydrogen has hitherto been obtained. + +But I had not the means of procuring this gas free of carbone, and +other impurities, that it dissolves and elevates during its formation; +or of excluding atmospheric air, which circumstances, I am sensible, +must, in some measure, influence the result; as it cannot be supposed, +that these extraneous bodies would remain inactive during the process +of reduction. However, as such exactness is not in the power of every +experimenter, I was under a necessity of using hydrogen gas, with the +disadvantages here mentioned. + +Though most of the experiments in this essay were made on a variety of +white and coloured silks, I shall relate only those made on the former, +as it exhibits the changes produced more distinctly, and contains less +foreign matter to modify the result of experiment; and, for brevity’s +sake, I shall use the term _silk_, by which _white silk_ is always +designed. + + +EXP. 1. GOLD. + +I poured a quantity of sulphuric ether on a solution of gold in +nitro-muriatic acid, and, by this means, obtained a solution of gold in +ether, which I separated from the acid. + +In this ethereal solution of gold, I dipped a piece of silk, after it +was taken out, and the ether evaporated, it was suspended in a tall +glass cylinder, placed over a vessel, containing a mixture of diluted +sulphuric acid, and iron filings. + +The silk thus exposed to a rapid current of hydrogen gas acquired, +after some time, a purple colour, and a large spangle of gold, of an +irregular figure, appeared on the upper end of the silk, and looked +very brilliant. + +The silk was kept exposed to the gas about four months, and frequently +observed, but no other remarkable change was perceived, except +that the purple colour became more intense: the experiment was now +discontinued; and on taking out the silk, and examining it in the light +of the sun, I observed many particles of reduced gold; but they were +very small, and by no means so brilliant, as that, which first appeared. + +During the experiment, fresh quantities of materials for supplying +hydrogen gas were occasionally added. + +From the brilliant spangle of reduced gold observed in this experiment, +I concluded, that there was a sufficient quantity of the metal in the +fibres of the silk, could it be reduced. + +This spot of reduced gold was very permanent, and adhered firmly to the +silk. + + +EXP. 2. GOLD. + +In order to determine, whether a solution of gold in ether, or one +in water, were best adapted to the object of these experiments; I +evaporated to dryness a solution of gold in nitro-muriatic acid, and +dissolved the salt in distilled water: in this solution, I immersed a +piece of silk, which, after it was dried in the air, was suspended in +a glass cylinder, like the former piece, and exposed to the action of +hydrogen gas about two months. + +The silk after some time assumed a purple colour, and five or six +specks of reduced gold, of the size of pin heads, and one much larger, +were observed. Examining the silk in the sun-beams, I perceived the +whole of it spangled with minute particles of reduced gold. + +After many experiments with these two solutions of gold, I was led to +conclude, that the solution in water answered best. + + +EXP. 3. SILVER. + +Having dissolved some pure silver in diluted nitric acid, and +evaporated some of the water by a gentle heat, I placed it in the dark +to crystallize. The crystals were separated from the solution, and +dissolved in distilled water; to one measure of this solution, which +was saturated with the nitrate of silver, ten or twelve measures of +distilled water were added. + +In this diluted solution, a piece of silk was dipped; after it was +taken out, it was dried at the fire: the silk dried in this manner, +retained its white colour; whereas, were it dried gradually in the air; +and especially, were the light considerable, its white colour would +be changed to a reddish brown, more or less intense, according to the +quantity of light present. + +Some kinds of silk, on being immersed in a solution of nitrate of +silver, have some of their threads immediately coloured brown: but I +often got white silk, which would retain its pure white colour, if +dried at the fire, or in the dark. + +The piece of silk dried, as above, was suspended in the middle glass of +Dr. Nooth’s machine; and into the lower glass were introduced a diluted +solution of sulphuric acid, and some small iron nails. + +The machine was now placed in a dark closet, to exclude the action of +light; after some time, the silk, thus exposed to hydrogen gas, put +on a light brown colour, which gradually became deeper, until it was +changed to a disagreeable black, with some mixture of brown: then very +small particles of reduced silver began to appear, which increased by +degrees, in number, and brightness. + +The experiment was continued four months; after which time, the silk +was taken out of the machine: it had a gray metallic appearance, +intermixed with a considerable tinge of brown. + +This experiment was repeated on another piece of silk, every +circumstance being the same, except that a quantity of water was put in +the middle glass of the machine, over which the silk was suspended; the +intention of interposing the water in this experiment was to purify the +gas. + +The appearances were much the same, as in the last experiment; except +that the silk became black sooner; and that some spangles of the +silver were larger, and better reduced. + +The specks of reduced silver were permanent, and adhered firmly to the +silk. + + +EXP. 4. LEAD. + +In a solution of acetite of lead in distilled water I dipped a piece of +silk, and dried it in the air; it was then suspended over a quantity of +water in Dr. Nooth’s machine, and exposed to hydrogen gas about three +months. + +The appearances were much the same as in the last experiment, except +that the silk was not so black: the particles of reduced lead resembled +silver. + +Similar experiments were made in this machine on bits of silk imbued +with a solution of nitro-muriate of gold in water; but the appearances +being much the same as those mentioned in the first and second +experiments, it is unnecessary to repeat them here. + +It is much easier to imagine, than express my anxiety, to discover +the cause of the brilliant specks of reduced gold and silver, with +which the pieces of silk in these experiments were sometimes spangled; +concluding, that were the cause ascertained, it would be a considerable +step towards accomplishing the object in view. + +But many and diversified were the experiments I made before the +circumstance, on which these spangles depended, was perceived. + +At length, I found it depended on the presence of moisture; and that +the spangles of reduced metal were owing to small drops of water +carried up by the elastic fluid, and deposited on the silk. + +The experiments, which led to this conclusion, shall be related in +their proper places. I shall now proceed to recite the remainder of the +experiments in this essay, conformable to the plan laid down in the +preface, premising an occurrence observed in the course of them. + +I sometimes found, that the production of hydrogen gas from a mixture +of acid, water, and iron nails, would unexpectedly stop, which induced +me to add more acid; this not succeeding, I added more water; but +still no gas was formed: the proportions of acid and water were varied +without effect. Thinking the mixture of acid and water unfit for the +purpose, I poured it off, and repeatedly washed and agitated the nails +with more water, which was also poured off; but happening inadvertently +to add some of the mixture of acid and water, which I had before poured +off as unfit for use, I was surprised to find the gas produced with +great rapidity. + +Reflecting on the cause of this odd circumstance, I concluded that it +depended on a crust of superoxygenated iron, formed on the surface of +the nails, which defended them from the action of the water and acid, +and that this crust was removed by the agitation and washing, which +enabled the diluted acid to act again on the iron. + + +EXP. 5. GOLD. + +I immersed a bit of silk in a solution of nitro-muriate of gold in +distilled water, and dried it in the air; it was then placed over a +cylindrical glass vessel, containing a mixture of diluted sulphuric +acid and iron nails, for about half an hour; but no reduction of the +metal could be observed. + +I dipped another bit of silk in the same solution of gold, and exposed +it, while wet, to the same current of hydrogen gas, and instantly +signs of reduction appeared; for the yellow colour, which the solution +imparts to silk, began to change to a green, and very soon a film of +reduced gold glittered on the surface opposed to the gas: shortly +after, a beautiful blue spot, fringed with orange and purple, was +formed on the middle of the silk. During the experiment, which lasted +about half an hour, the silk was kept constantly wet with distilled +water. + +When experiments are made with this preparation of gold, it is +necessary to evaporate the solution to dryness, before the salt be +dissolved in the water; as an excess of acid prevents the reduction in +a great measure. Solutions of gold in these experiments do not admit of +being so largely diluted, as solutions of silver, and other metals do. + + +EXP. 6. SILVER. + +I immersed a piece of silk in a solution of nitrate of silver, and +dried it in a dark place; it was then exposed to a current of hydrogen +gas about twenty minutes; but no reduced silver appeared, the only +change observable was a brown stain. + +I immersed another bit of the same silk in the same solution of +silver, and having exposed it, while wet, to a stream of hydrogen gas, +I soon observed evident signs of reduction; the white colour of the +silk was changed to a brown, which became gradually more intense; and +the surface of the silk, opposed to the gas, was coated with reduced +silver: various colours, as blue, purple, red, orange, and yellow, +attended the reduction. These colours often change, and are succeeded +by others in the progress of the reduction. The threads of the silk +look like silver wire, tarnished in some parts, but of great lustre in +others. + +The silk was kept wet with distilled water during the experiment. When +the silk happened to be too much wetted, the under surface opposed to +the gas was often covered with scales of a dull blue colour: these, +after the silk dries, may be brushed off, and another coat of reduced +silver, which adheres firmly, but has no considerable brightness, is +left behind. + +These experiments on the reduction of gold, and silver, were often +repeated with nearly the same result. + + +EXP. 7. SILVER. + +Thinking some other preparation of silver might answer better than a +nitrate, I precipitated some of the latter with a solution of muriate +of soda, and poured the whole on a filter; the precipitate was well +washed with distilled water, and dissolved in ammonia. In this solution +I immersed a piece of silk, and dried it in the air; and having +exposed it to the action of hydrogen gas, I could perceive no signs of +reduction, except a faint brown colour. + +I dipped another bit of silk in the same solution of silver, and in +order to determine if water had the power of promoting the reduction of +the silver in this preparation, as it had in the former experiments, I +exposed the silk, while wet, to the same current of hydrogen gas; and +in a few seconds the metallic lustre was evident on the surface opposed +to the current. After some little time, a blue speck and a faint trace +of yellow appeared, but soon vanished. + +This preparation of silver does not stain white silk so much as a +nitrate does; the reduced silver was indeed very brilliant, but soon +grew dull, and disappeared; a brown stain only remaining; so that +it seems rather inferior to nitrate of silver, which also, after +reduction, tarnishes, grows dull, and often disappears; but sometimes +part of it remains permanently reduced. + + +EXP. 8. PLATINA. + +With much difficulty I procured a small quantity of the ore of platina, +and dissolved it in nitro-muriatic acid. The solution was evaporated to +dryness, and the salt was then dissolved in distilled water. + +A bit of silk was dipped in part of this solution, and dried in the +air; it was then exposed to a brisk current of hydrogen gas about +twenty minutes, but no signs of reduction appeared. + +Another bit of silk was immersed in the solution of platina, and +exposed, while wet, to the same current of hydrogen gas; in five or +six minutes the platina was reduced, exhibiting a livid white metallic +appearance on the surface of the silk opposed to the current. No +colours attended the reduction. This solution imparts a yellowish brown +colour to silk. + +After some time, the whole of the metallic lustre disappeared, in +proportion as the silk became dry. + +The solution of platina requires more time, and a stronger current of +hydrogen gas for its reduction, than solutions of silver and gold do. + + +EXP. 9. MERCURY. + +I immersed a bit of silk in a solution of oxygenated muriate of mercury +in distilled water, and dried it in the air: it was then exposed to a +stream of hydrogen gas; but underwent no visible change. + +I dipped another bit of silk in the same solution of mercury, and +exposed it, while wet, to the same current of gas; the metal was soon +reduced in a beautiful manner, and resembled silver. + +The reduction began suddenly, with scarce any appearance of previous +stain; some very faint, but at the same time transparent colours +attended it: the most remarkable of these were a light orange, with a +fringe of blue, and a yellow verging on a faint green. These colours +soon disappeared. + +After the silk was turned, I observed, that its texture was, in some +parts, concealed by a thin film, which, as the reduction proceeded, +was perceived to dart along the threads of the silk, gilding them in a +beautiful manner, and exhibiting the texture very distinctly. + +After some time, the mercury seemed to disappear, so as to render it +doubtful whether any of it remained in the silk; but shaking it in the +sunbeams, I perceived bright atoms fly off; and rubbing the silk on a +bit of blue paper, I observed shining metallic particles, which seemed +to have lost their affinity of aggregation, for they did not unite. + +One remarkable difference between this preparation of mercury and +nitrate of silver, is, that no black or brown stain preceded, attended, +or followed, the reduction of the mercury. + +Mr. Scheele reduced a prussiate of mercury, dissolved in water, by +adding iron filings and a small quantity of sulphuric acid to the +solution[9]. + + +EXP. 10. COPPER. + +A piece of silk was immersed in a solution of sulphate of copper, then +taken out, and dried, and exposed for a considerable time to a brisk +current of hydrogen gas; but no signs of reduction could be perceived. + +Another bit of silk was dipped in the same solution of copper, and +exposed, while wet, to the same rapid current of hydrogen gas; the +appearances were the following. + +After a minute, or two, the silk assumed a faint brown colour, and, on +the surface opposed to the gas, a white metallic pellicle appeared, +which vanished in proportion as the silk became dry: wetting the silk +again, I perceived a similar pellicle appear, which also vanished, as +soon as the silk dried. If the silk be kept constantly wet, the brown +colour becomes much more intense, attended with a very slight tinge of +red. The margins of the silk projecting beyond the verge of the glass +cylinder, and therefore not exposed to the current of the gas, retained +the blue colour, which the solution imparts. + +In some of these white metallic pellicles there appeared a faint brown +inclining to yellow, which reflected the light, though obscurely. + +After the silk dried, nothing remained, but a brown stain. + + +EXP. 11. LEAD. + +A piece of silk was immersed in a solution of acetite of lead in +distilled water; it was then dried, and exposed for some time to a +stream of hydrogen gas; but underwent no perceptible change. + +Another bit of silk was dipped in the same solution of lead, and +exposed, while wet, to the same current of hydrogen gas; in a second, +or two, the surface of the silk, opposed to the current, was coated +with reduced lead, which looked like silver. + +The reduction was accompanied with a brown stain, but by no means so +intense as that, which attends the reduction of nitrate of silver. + +The other side of the silk was opposed to the current of hydrogen gas, +and soon acquired a metallic coat of the same brilliant appearance, +exhibiting the texture of the silk, in a very striking manner. + +It is remarkable, that lead exhibits no colour, but a light brown, +during its reduction; whereas gold, silver, and mercury, display a +great variety of colours, especially the two former. + +After some time the lead reduced in this manner loses its metallic +splendour considerably; and that in proportion as the silk dries. + + +EXP. 12. TIN. + +I dissolved some crystals of muriate of tin in distilled water; dipped +a bit of silk in the solution; and dried it in the air: it was then +exposed to a stream of hydrogen gas a considerable time; but no change, +or appearance of reduction, could be observed. + +Another bit of silk was immersed in the same solution of tin, and +exposed, while wet, to the same current of gas; after some little time, +the reduction commenced, attended with a great variety of beautiful +colours; as red, yellow, orange, green, and blue, variously intermixed. + +The reduced tin disappears along with these colours, as the silk dries; +nothing remaining but a feuille-morte colour. + +The same solution of tin was also reduced by hydrogen gas, obtained +from tin, and the muriatic acid. + +These experiments do not succeed well with muriate of tin containing an +excess of acid. + + +EXP. 13. ARSENIC. + +A muriate of arsenic, which was prepared by digesting white oxid of +arsenic in muriatic acid, and continuing the heat, till most of the +acid evaporated, and left behind a soft mass of the consistence of tar, +was dissolved in distilled water. + +In this solution a bit of silk was immersed, and dried in the air: it +was exposed to a brisk stream of hydrogen gas, obtained from zinc, and +muriatic acid; but no reduction took place. + +Another bit of silk was dipped in the same solution, and exposed, while +wet, to the same current of hydrogen gas; and instantly, the surface of +the silk, opposed to the gas, was covered with a bright coat of reduced +arsenic, accompanied with a yellow stain. In a short time the metallic +lustre vanished; and nothing remained but the yellow stain. + +M. Pelletier restored the acid of arsenic to its metallic state, by +passing hydrogen gas through a solution of that acid, in twice its +weight of water[10]. + + +EXP. 14. BISMUTH. + +A bit of silk, which was immersed in a solution of nitrate of bismuth +in distilled water, and exposed dry to hydrogen gas, obtained from +zinc, and muriatic acid, underwent no visible change. + +Another bit of silk was dipped in the same solution of bismuth, and +placed over a languid stream of hydrogen gas; the bismuth was soon +restored to its metallic form, on the surface of the silk opposed to +the elastic fluid. The reduction was attended with a reddish brown +stain, intermixed with a tinge of violet. + + +EXP. 15. ANTIMONY. + +A bit of silk was immersed in a solution of tartarite of antimony in +distilled water; and dried in the air. It was then exposed to hydrogen +gas, obtained from zinc, and muriatic acid; but suffered no visible +alteration. + +Another bit of silk, which was dipped in the same solution of antimony, +was exposed wet to a weak stream of the gas; and, in a short time, the +metallic lustre appeared, accompanied by a light yellow colour. + + +EXP. 16. IRON. + +A bit of silk, which was immersed in a largely diluted solution of +sulphate of iron, and dried in the air, was exposed to a strong +current of hydrogen gas, obtained from iron nails, and diluted +sulphuric acid; but no visible change was produced on the silk. + +Another bit of silk was dipped in the same solution of iron, and placed +wet over the same stream of hydrogen gas; but no reduced iron could be +perceived. The silk was then immersed in a glass of clear water, and +transferred a very minute metallic film to the surface of that fluid. + +This experiment was repeated with a rapid current of hydrogen gas, +obtained from zinc, and muriatic acid; and, in about a minute, small +films of reduced iron were visible on the surface of the silk, opposed +to the gas. + +The silk was then immerged in water, and transferred to its surface a +large metallic pellicle; parts of which were very brilliant; but other +parts were dull, and much more imperfectly reduced. + + +EXP. 17. ZINC. + +A bit of silk, which was dipped in a muriate of zinc, largely diluted +with water, and dried in the air, was exposed to a rapid current of +hydrogen gas, obtained from zinc, and muriatic acid; but suffered no +visible alteration. + +Another piece of silk was immersed in the same solution of zinc, and +exposed, while wet, to the same rapid current of hydrogen gas: in +about half a minute, the metal was reduced in a very evident manner, on +part of the silk. The silk was then dipped in a glass of clear water, +and transferred a bright metallic film to its surface. + +As these reductions of iron, and zinc, by hydrogen, are contrary to M. +Lavoisier’s table of the affinities of the oxygenous principle; I began +to suspect, that the films, which were so evident, both on the silk, +and the water, might be abraded, or torn from the zinc, by the muriatic +acid; and elevated, and deposited on the silk by the gas. + +In order to remove this doubt, I dipped a bit of the same silk in +distilled water; and exposed it, while wet, to the same current of +hydrogen gas, but nothing metallic could be seen on the silk; nor did +it when immersed in water transfer a film, or the smallest appearance +of a metal, to the surface of that fluid: and, therefore, there can be +no doubt of the reality of these reductions. + +Dr. Priestley restored iron, and lead, to their metallic state, by +heating their oxids with a burning glass in hydrogen gas. + +These experiments point out an error in M. Bergman’s table of elective +attractions in the humid way; for he assigned the last place in that +table to phlogiston, which he considered as the base of inflammable +air; because he was unacquainted with any metallic reductions effected +by hydrogen in the humid way[11]. + +Having found, that water promoted, and accelerated, these reductions in +a very remarkable manner; I was curious to know, if alcohol, and ether, +would produce the same effect. With this view, I evaporated a solution +of gold in nitro-muriatic acid to dryness; when the vessel cooled, some +alcohol was poured on to dissolve the salt; and immediately the vessel +containing the salt, became so hot, that it could be scarcely endured +by the hand; and diffused a fragrant smell, like that of ether, which, +no doubt, was a species of that fluid. + + +EXP. 18. GOLD. + +In this solution of gold in alcohol, a bit of silk was dipped, and +exposed to a stream of hydrogen gas, obtained from diluted sulphuric +acid, and iron nails; and kept wet with alcohol: in about two minutes, +the silk began to assume a brown colour, and white metallic films +appeared on some parts of the surface opposed to the gas; some of these +disappeared in a short time; and were succeeded by a few very small +spangles of the proper colour of gold. These also soon vanished; and +nothing remained but a disgreeable brown stain, intermixed with specks +of a dull blue. + +I sometimes found, on repeating this experiment, that no yellow films +or spangles appeared; and am persuaded, that their appearance, and +that of the white pellicles also, depends on the presence of water, +contained in the alcohol, or the gas, and deposited on the silk. + + +EXP. 19. GOLD. + +A bit of silk was immersed in a solution of gold in ether, and exposed +to a stream of hydrogen gas, and kept wet with ether. The silk +underwent no alteration for a few minutes; at length, it began to +assume a faint brown colour, but no white, or yellow films appeared. + +If this experiment be continued till the silks collects a sufficient +quantity of water from the gas, some films will appear. + + +EXP. 20. SILVER. + +I procured some nitrate of silver, which had been fused in order to +expell as much of its water as possible; and dissolved it in alcohol. I +immersed a bit of silk in this solution, and exposed it to a stream of +hydrogen gas, and kept it wet with alcohol: in a few seconds, the silk +assumed a brown colour, which gradually became more intense: but no +reduced silver appeared for several minutes; at length, a few metallic +films appeared on part of the surface opposed to the gas. + + +EXP. 21. MERCURY. + +A bit of silk was dipped in a solution of oxygenated muriate of +mercury, and dried; it was then exposed to hydrogen gas about ten or +fifteen minutes, and kept constantly wet with alcohol. The silk, during +the first minutes, suffered no perceptible alteration: at length, a few +small films were visible on the side of the silk opposed to the current. + + +EXP. 22. LEAD. + +A bit of silk, which was immersed in a solution of acetite of lead, +and dried, was exposed about fifteen minutes to a stream of the gas; +and kept constantly wet with alcohol; but suffered no visible change; +except that a very minute film was reduced on one of its margins, which +did not project beyond the verge of the glass vessel on which it was +placed. + +When we compare these experiments with those, in which water was +used, to wet the silk, ’tis evident, that alcohol, and ether, do not +promote the reduction of metals, as water does; and that the few films, +which appear, when the silk is kept wet with ether or alcohol, depend +entirely on water collected from the gas, or deposited by them on the +silk during their evaporation. + +In order to compare the effects of hydrogen gas, obtained from water, +iron nails, and muriatic acid, with that, procured from the same +materials, by means of the sulphuric; I made some experiments on gold, +silver, mercury, and lead, in the same manner, as the preceding; and +the principal difference was, that the colours produced in all the +pieces of silk, except that, which was dipped in acetite of lead, +were much brighter, and more beautiful, than any produced, when the +sulphuric acid was used. + +The reduction of the lead was accompanied with its usual brown colour. + +On the upper surface of a bit of silk, which was dipped in a solution +of gold, a green colour instantly appeared; and soon changed to a deep +olive, in proportion as the reduction advanced: now examining the +under surface, I saw it coated with a bright film of reduced gold, in +the middle of which a blue spangle, mixed with purple, soon began to +appear: I then moistened the upper surface of the silk with water; and +in a few seconds, it also was coated with reduced gold. + +The blue on the other side of the silk became much more intense: the +piece was now turned; and on each colour I let fall a drop of water: +the drop on the blue had a blue film, the drop on the purple, had a +purple film, and the drop on the yellow, a film of reduced gold. + +After some time, these drops of water evaporated, and the films came +again in contact with the silk: some parts of which were left bare, as +generally happens, when too much water is applied. + +On the under surface of a bit of silk, which was immersed in a solution +of nitrate of silver in water, a coat of reduced metal was formed, with +various colours, as green, blue, orange, and yellow, the beauty and +brightness of which were remarkable. + +In some time a muriate of silver is formed in the fibres of the silk, +which on exposure to light becomes of a bluish black colour: but the +whole of the silver does not undergo this change; for part of it +remains in its metallic state. The colours remain a considerable time, +if the silk be removed from the gas before this muriate is formed. + +Hence it appears, that hydrogen gas should not be prepared with an +acid, which forms an insoluble compound with the metal to be reduced. + +I also found, that hydrogen gas produces different effects not only +according to the difference of the acid, but also according to the +difference of the metal employed to obtain it: for this gas procured +from zinc or tin, and muriatic acid, did not restore gold to its proper +metallic lustre; but formed on the silk, a white metalline coat like +silver. + +The experiments related in this chapter indicate the following +conclusions. + +1. Hydrogen is capable of reducing the metals in the ordinary +temperature of the atmosphere. + +2. Water promotes, and accelerates, these reductions, in a very +remarkable manner. + +3. Ether, and alcohol, do not promote these reductions, without the aid +of water. + +4. A variety of colours accompanies these reductions, similar to what +appears, during the calcination of metals by heat and air; and depends +on the same cause: viz. the quantity of oxygen combined with the metal. + +These colours have not been observed hitherto; nor indeed could they; +as the metals were reduced in close vessels, and in high degrees of +heat. + +5. These reductions often disappear. + +This is commonly owing to an imperfect, and partial reduction of the +metal: for the acid, and water, remaining in that part of the metallic +solution, not reduced, recalcines these delicate films: sometimes the +disappearance of the metallic lustre depends on the nature of the +metal itself: thus arsenic, lead, silver, &c., suffer some degree of +calcination by water and atmospheric air. + +Messrs. Bergman and Keir relate instances, in which silver after being +precipitated in its metallic state, was recalcined, and disappeared. + +I first imagined, that water promoted these reductions by minutely +dividing the particles of the metallic salt, and by condensing the +gas, and bringing its hydrogen, and the metallic oxid, within the +sphere of attraction; the hydrogen either uniting to the metallic +earth and reducing it, as the Phlogistians suppose; or uniting with, +and separating the oxygen of the metal, and thus restoring it to the +metallic form, as the Antiphlogistians maintain. + +But it is evident from the experiments related, that water does not +promote these reductions solely, by minutely dividing the particles of +the metallic salt: for were this the case; ether, and alcohol, should +promote the reduction of the metallic salts, which they dissolve, since +they divide their particles, as minutely as water can. + +Since then metallic solutions in ether, and alcohol, cannot be reduced +by hydrogen gas; it follows that the above supposition concerning the +mode of agency of water does not account for the reduction of metals in +this way. + +And indeed were it true that hydrogen condensed by water reduced metals +in the manner above mentioned, it would follow, that the reduction was +effected by a single affinity, which cannot be admitted; 1st. because +the existence of a single affinity in such cases has not been proved; +2dly, because a double affinity always takes place in preference to +a single affinity, which is demonstrated by the following facts, +transcribed from the works of Mr. Kirwan. + +“If a solution of silver in the nitrous acid be thrown into a mixed +solution of fixed alkali and common salt, the silver will be +precipitated by the marine acid of the common salt, and not by the free +alkali, contained in the liquor: for a luna cornea is found[12].” + +“I repeated the experiment with a solution of lead, and also of mercury +in the nitrous acid, and the result was similar: both lead and marine +salt of mercury were formed[13].” + +In these experiments of Messrs. Monnet and Kirwan, ’tis evident that +a double affinity takes place in preference to a single one: for the +nitrous acid of these different nitrates unites with the alkali of the +common salt, while the muriatic acid of the latter seizes the silver, +mercury, and lead, of the nitrates, and forms muriates of silver, +mercury, and lead: the free alkali remaining passive in the mixture. + +M. Lavoisier says, “There exists only in nature, as far as we can +observe them, cases of double affinity, often triple, and others +perhaps still more complicated[14].” + +Now as water does not promote these reductions merely by dissolving, +and minutely dividing, the particles of the metallic salts, and +condensing the hydrogen gas; and since a double affinity takes place in +preference to a single affinity; it is obvious that the water must be +decomposed in these reductions in the following manner. + +The hydrogen of the gas unites to the oxygen of the water, while the +hydrogen of the latter unites in its nascent state to the oxygen of the +metal, reduces it, and forms water. + +Thus what could never be effected by a single, is readily performed by +a double affinity. + +Hence it follows, that the hydrogen of the gas is oxygenated by the +oxygen of the water, while the metal is, at the same time, restored +to its combustible state. It also follows, that the quantity of water +formed is double that decomposed. + + + + +CHAPTER II. + +_Reduction of Metals by Phosphorus._ + + +The next substance, of whose effects in reducing metals in the fibres +of silk, I shall treat, is Phosphorus, one of the most inflammable +substances, we are acquainted with. + +I was for some time at a loss, how to apply it to this purpose; but +learning from a note of Mr. Lewis, that it is soluble in ether; I +dissolved a small quantity of it in that fluid, which can be easily +effected, if the ether be good. The solution is considerably promoted +by a gentle heat, as that of the hand, and may be made in a small +phial, which should be nearly filled with the ether, and accurately +corked: a common cork is preferable, for this purpose, to a glass +stopper; and a single grain of phosphorus is sufficient for a great +number of experiments. + +I sometimes applied a much greater degree of heat than the above, by +placing the phial in hot sand, pressing on the cork at the same time +with my finger, to prevent its being forced out by the expansion of the +ether, part of which is converted into an elastic fluid, and holds some +phosphorus in solution: the ether soon begins to boil; the phosphorus +melts; and a strong solution is obtained in a few minutes by shaking +the phial. If the solution be removed to a cool place it frequently +deposits crystals. + +This manner of preparing the solution is attended with some danger; for +should the phial burst, or the cork be extruded, the contents will be +thrown out with considerable force, and that part of the phosphorus not +dissolved by the ether burn with great violence. + +The only objection to this preparation of phosphorus is the ether, +which must necessarily modify the result, and prevent that simplicity +so desirable in experiment. + +But, after some observation, it was perceived, that the ether flies +off, and leaves the phosphorus pure, and minutely divided in the fibres +of the silk: the ether, from its great volatility, first evaporates, +and, at the same time, produces a very considerable degree of cold, +which effectually prevents the evaporation, and combustion, of the +phosphorus. + +After the ether evaporates; the cold ceases, and the combustion of the +phosphorus commences, attended with white fumes, which continue till +the whole is consumed, if no other power intervene. + +Hence it is evident, that this preparation of phosphorus has a +simplicity, and elegance, not always to be obtained. + +It has also another great advantage in experiments of this kind; for +it does not change, in the smallest degree, the white colour of silk, +during its slow combustion, which is not attended with heat sufficient +to affect the most delicate colour. This property of not affecting the +colour of the silk renders observation, and experiment, more accurate; +as whatever change supervenes, must depend either on the metallic +solution itself, or on the action of the phosphorus on the same. But +this advantage is confined to a certain range of the thermometer; for +if the heat be increased to about 86° of Fahrenheit, and the silk be +dry, the phosphorus is apt to set fire to it. + + +EXP. 1. GOLD. + +I immersed a bit of silk in a solution of gold in ether, and after the +ether evaporated, dropped on it some of the solution of phosphorus, +which diffused itself through the silk, like a drop of oil, and formed +a circumscribed spot, whose limits, as the ether evaporated, assumed +a brown colour, which soon diffused itself equally over every part, +to which the solution of phosphorus was applied; but the parts of the +silk, to which the latter did not reach, retained the yellow colour, +which the solution of gold gave them. + +The silk viewed by transmitted light presented the same colours, except +that the limits of the brown appeared more intense, and seemed to +border on a faint purple. + +Examining the silk next day, I found, that the whole of the brown stain +acquired a faint shade of purple, which was most evident on the margins +of the stain. + + +EXP. 2. GOLD. + +I dipped a bit of silk in the solution of gold in ether, and after it +was well dried, half of it was wetted with distilled water; the other +half remaining dry: the solution of phosphorus was applied to both the +moist and dry parts of the silk: instantly the part wetted with the +water began to acquire a purple colour; and, soon after, the metallic +splendour of the gold appeared; but that part, which was kept dry, +acquired only a brown stain, similar to that described in the preceding +experiment. + +I repeated these experiments many times, and always found, that the +gold was reduced only in proportion to the water applied. + +Finding water promoted the reduction of gold by phosphorus, I began to +form various conjectures about its mode of action: I first supposed, +it acted by holding the particles of the salt minutely divided, thus +diminishing their attraction of cohesion, and consequently increasing +their chymical attraction. + +The truth of this supposition might, I thought, be decided by using +ether, and alcohol, instead of water, to wet the silk, avoiding +aqueous moisture, as much as possible; accordingly, I made the +following experiments, which were frequently repeated with nearly the +same result. + + +EXP. 3. GOLD. + +A piece of silk was immersed in the solution of phosphorus; as soon as +the ether evaporated, and the phosphorus began to fume, an ethereal +solution of gold was dropped on the silk, which immediately got a brown +colour; the piece was kept constantly wet with ether; in some time a +purple tinge appeared on parts of the silk; and, shortly after, small +films of reduced gold appeared: the silk was now remarkably wet, and +seemed to have a great power of collecting water; this, I supposed, was +partly attracted from the air by the salt, and phosphorous acid formed +during the combustion, which has a powerful attraction for water; and +partly deposited in the silk by the ether during its evaporation. + +In order to determine if the ether during its evaporation deposited +water in the silk, I kept a bit of silk wet with ether for a few +minutes, and found, that, after the evaporation ceased, the silk was +moist: but this humidity was not so great, as that observed in the +silk, to which the ethereal solutions of phosphorus, and gold, were +applied. + +Another bit of silk was dipped in the ethereal solution of gold, and +after the ether evaporated, the solution of phosphorus was applied: a +brown colour was produced; the silk was kept wet with ether, and, in a +short time, a purple tinge appeared on parts of it; but chiefly at the +margin of the stain, which gradually diffused itself over the whole. + +The only difference between this and the preceding experiment on gold +is the order, in which the solution of gold, and phosphorus, were +applied to the silk; but there is a considerable difference in the +result; for in this the brown and purple colours were formed much more +slowly, and no particles of reduced gold appeared till after a much +longer time. + + +EXP. 4. GOLD. + +A piece of silk was immersed in the solution of phosphorus, and when +the white fumes began to rise, a solution of gold in alcohol was +applied to the silk, which was kept wet with alcohol; a brown tinge, +which soon changed to a purple, appeared on different parts; and, in a +little time after, a very small film of reduced gold was visible on a +part of the margin. + +In another experiment, conducted in the same manner, the reduction was +more evident. + +The solution of gold used in this experiment was very rich; and had +a great attraction for water; for bits of silk tinged with it, could +not be dried without difficulty; and after they were removed to a cool +place, they very soon became moist again. This is more or less the case +with solutions of gold in general. + + +EXP. 5. GOLD. + +A bit of silk was dipped in a solution of gold in alcohol, and dried; +then some of the solution of phosphorus was poured on the silk; a +brown, and then a purple colour, appeared; and in some parts a small +portion of the gold was reduced: the reduction was very obscure; but +became gradually more evident, in proportion as it attracted water from +the air. The silk was occasionally wetted with alcohol. + +This experiment was repeated, with this difference, that the silk was +not kept wet with alcohol; and no reduced gold could be perceived. + + +EXP. 6. GOLD. + +In order to exclude water more effectually, a small phial was carefully +dried by placing it in hot sand, and then corked, to prevent the access +of moisture from the air; when the phial cooled, it was nearly filled +with ether, and a small bit of phosphorus dropped into it; it was then +corked, and replaced on the hot sand; the phosphorus soon melted, and +a strong solution was obtained by shaking the phial. + +Into this solution a small bit of silk, which was dipped in a rich +solution of gold, and carefully dried, was introduced: the silk +immediately got a brown tinge; but not a particle of reduced gold could +be perceived. The solution in a short time became turbid, and deposited +a brown powder. The colour of the precipitate was exactly the same, as +that which the silk acquired. The experiment was continued about three +months, and carefully observed; but no other change could be perceived: +at the end of this time the silk was taken out of the phial; and the +solution of phosphorus was found capable of reducing gold and silver by +the aid of water. + + +EXP. 7. GOLD. + +In order to contrast the effects of water with those of ether, and +alcohol, more fully, a piece of silk was immersed in a solution of +nitro-muriate of gold in water, and dried in the air about twelve +hours; during which time the yellow tinge, the solution of gold gave +the silk, remained unchanged: the solution of phosphorus was then +applied; a brown stain appeared; the ether soon evaporated; the +phosphorus began to fume; and the silk acquired a purple colour; but +not a particle of reduced gold could be perceived. The purple tinge +in this bit of silk was much more intense, and more equal, than in the +pieces, in which ether and alcohol were used. + + +EXP. 8. GOLD. + +I dipped a piece of silk in the solution of phosphorus, when the ether +evaporated, and the phosphorus began to fume, a solution of gold in +water was applied; instantly the silk was covered with a splendid coat +of reduced gold. + +Nothing can be more striking than this experiment, which was repeated +times without number, or demonstrates the necessity of water in these +reductions in a more convincing manner. + +This piece, viewed by transmitted light, had a purple colour with a +considerable tinge of blue; and the margin of the reduced gold was +fringed with purple. + + +EXP. 9. GOLD. + +Thinking that phosphorus applied in the form of vapour through the +medium of water might be more effectual than a solution of it in ether, +I immersed a small bit of silk in an aqueous solution of gold, and +suffered it to dry a little; it was then suspended in a phial over +a little water, into which a small bit of phosphorus was previously +introduced: the phial was then corked, and placed on hot sand: the +phosphorus began to melt, and ascend in white vapours, which, as soon +as they reached the lower end of the silk, gave it a brown tinge, +succeeded by a purple; and the gold began to assume its metallic +splendour: in a short time these appearances were evident over the +whole silk. + +The following propositions are deducible from these experiments. + +1. Water does not promote the reduction of gold merely by dissolving, +and minutely dividing, the particles of the salt, and thus diminishing +their attraction of cohesion, and consequently increasing their +chymical attraction, as I first supposed; for were this the case, ether +and alcohol, which equally dissolve, and divide, the salt, should +produce the same effect. + +2. Ether and alcohol do not promote these reductions without the aid +of water; for it is evident from the experiments related, that the few +particles of reduced gold, which appear, when they are employed, depend +entirely on the quantity of water, which they leave in the silk during +their evaporation, and that attracted from the air by the solution of +gold, and by the phosphorus during its combustion, both of which have a +strong attraction for water. + +3. Phosphorus does not reduce gold by giving the metallic earth +phlogiston, as the Phlogistians suppose; for were this opinion true, +a solution of gold in ether, or alcohol, should be reduced by the +phosphorus as effectually as a solution of gold in water is. + +4. Phosphorus does not reduce gold, by combining with, and separating, +the oxygen of the gold, as the Antiphlogistians assert; for were +this the case, the particles of the phosphorus so attenuated by the +ether, should reduce a solution of gold in ether, or alcohol, as well +as a solution of gold in water, since the impediment opposed by the +attraction of cohesion is equally removed in both cases. + +I shall conclude these remarks on the reduction of gold with the +following experiment, which often amused me. + + +EXP. 10. GOLD. + +A small bit of silk was immersed in a solution of gold in ether, and +dried; then the solution of phosphorus was applied, which changed the +yellow colour of the silk to a brown: when the phosphorus began to +fume, I placed the silk on the palm of my hand, and breathed on it a +considerable time; a purple tinge gradually succeeded the brown, and, +in some little time after, the metallic lustre of the gold began to +appear. + +The same experiment succeeds with a solution of gold in alcohol. + +Another bit of silk, treated in the same manner, was placed over the +vapour of warm water for some time; the same appearances took place, +and particles of reduced gold were evident in the silk. + +If the water, whence the vapour arises, be too hot; the heat retards, +and sometimes prevents, the reduction, by volatilizing the phosphorus. + + +EXP. 11. SILVER. + +I dipped a bit of silk in a solution of fused nitrate of silver +in alcohol, and dried it in the air: then some of the solution of +phosphorus was applied, which produced a brown stain, whose margin, +after a few minutes exposure to the air, acquired a livid white +appearance, caused by a partial and imperfect reduction of the silver. + +This, however, would not be taken by a person unacquainted with +experiments of this kind for reduced silver. + + +EXP. 12. SILVER. + +A bit of silk was immersed in the solution of phosphorus; as soon as +the ether evaporated, and the phosphorus began to fume; a few drops of +the solution of silver in alcohol were applied: immediately a black +stain, intermixed with some brown, appeared: and, after some time, +obscure films of reduced silver presented themselves; these appeared +on different parts of the stain; but were so minute as to be scarce +visible. The only difference between this and the preceding experiment +is the order, in which, the solutions were applied; but even this +modifies the result in some measure. + +That these imperfect reductions depended on water, deposited in the +silk, by the alcohol during its evaporation, or attracted from the air +by the phosphorus during its combustion, will appear from the following +experiment. + + +EXP. 13. SILVER. + +A small phial was well dried in hot sand, then corked, and removed to +a cool place; after the phial cooled, it was nearly filled with ether, +and a small bit of phosphorus, which was repeatedly washed in alcohol +to free it from any aqueous moisture, that might adhere to it, was +introduced; the phial was then corked, and placed in hot sand; when the +phosphorus melted, I shook the phial, and obtained a strong solution. + +Into this solution a small bit of silk, which was dipped in a solution +of silver in alcohol, and dried, was introduced: the phial was corked; +the silk instantly assumed a brown colour; but not a particle of +reduced silver could be seen, though the experiment was continued about +three months; nor did the solution of phosphorus become turbid, or +deposit any precipitate, as happened in similar experiments on gold. + +At the end of this period the silk was taken out of the phial, wetted +with water, and suspended in a window; and, after a considerable time, +reduced silver was manifest on different parts of the silk. + +With the solution of phosphorus, in which the silk stood during that +time, I reduced gold, and silver, with the assistance of water. + +In order to compare the effects of water with those of ether and +alcohol, I made the following experiments. + + +EXP. 14. SILVER. + +I dipped a bit of silk in a solution of nitrate of silver in water, +and dried it at the fire: the silk thus dried retained its white +colour: the solution of phosphorus was then applied, and immediately +produced a brown colour, which soon, in proportion as the phosphorus +fumed, acquired a deeper tinge, verging on black; and slight signs of +reduction appeared after a little time on the margin of the stain. + +Another bit of silk, treated in the same manner, but dried much better, +exhibited still fainter signs of reduction: for the brown stain did not +appear on this piece as soon as on the former, nor was it so intense; +however, after some minutes exposure to the air, the stain became +deeper, and its margin acquired a livid white appearance, owing to a +partial reduction of the silver. + +It has been often remarked, that the reduction commences first on the +margin of the stain, which the solution of phosphorus, and that of the +metal, produce in the silk: I was a long time at a loss to account +for this appearance; but the cause was accidentally discovered; for +happening to spill a few drops of the solution of phosphorus on a +table, I observed, that, as they evaporated, watery circles were formed +round the spaces, on which the drops fell; and, that all the parts +within the circles were dry. + +This explains why the reduction begins on the margin of the stain. + +I observed the same of alcohol; for if it be dropped on a level +surface, it leaves a watery ring behind, though not near so soon, as a +solution of phosphorus in ether does: this is the reason why alcohol +seems to promote the reduction of some metals; I say seems; for it +does not promote it, but in proportion to the quantity of water it +contains, or attracts from the air, and deposits in the silk during its +evaporation. + +How essential water is to the reduction of metals will appear from the +following experiment. + + +EXP. 15. SILVER. + +I immersed a piece of silk in the solution of phosphorus, and after +the ether evaporated, and the phosphorus began to fume, a solution +of nitrate of silver in water was applied; instantly the silver was +restored to its metallic splendour. + +This experiment is very amusing, and well calculated to strike the +beholder with surprise. + +The reduction is sometimes attended with spangles of a beautiful blue, +which appear chiefly where the solution of silver is most abundant. + +The solution of silver is commodiously applied by a camel hair pencil. + +I also tried the effects of the vapour of phosphorus on bits of silk +dipped in a solution of nitrate of silver in water, and exposed to the +vapour, in the same manner as in experiment the 9th; and the silver was +always reduced: but a solution of phosphorus in ether seems preferable +to the vapour. + +A small glass tube, resembling a thermometer, with its bulb terminating +in a smaller and nearly capillary tube, I found useful, and economic, +especially in experiments on gold: by immersing the smaller end in the +metallic solution, and inspiring through the tube at the same time, the +bulb may be filled: by this means a single drop, or more, if necessary, +may be applied to the silk; and, thus, a great number of experiments +can be made on a single grain, or a much less quantity, of gold, or any +other metal. + +This little instrument may be used also to apply the solution of +phosphorus to the silk; and it was by using it for this purpose, +I discovered, that phosphorus has not the power of reducing silver +without the aid of water; for blowing the solution of phosphorus from +the tube on bits of silk, which had been dipped in a solution of +silver, and dried, I was surprised to find films of reduced silver +frequently appear; whereas none appeared, when I applied the solution +of phosphorus in a different manner: this unexpected event often +occurred, before I learned the cause; at length I suspected, it might +depend on the moisture of the breath; and I was soon convinced by +moistening the silk with water, that the suspicion was well founded. + +It is evident from these experiments on silver, that water is essential +to the reduction of this metal by phosphorus; and that ether, and +alcohol, do not promote it. + +It is also evident, that these experiments, and those, made on the +reduction of gold, mutually illustrate each other; and confirm the +conclusions drawn from them. + + +EXP. 16. PLATINA. + +I immersed a bit of silk in a solution of nitro-muriate of platina in +distilled water, and dried it in the air; the solution of phosphorus +was then applied to the silk; but no appearance of reduction could be +perceived. + +Another bit of silk was dipped in the solution of phosphorus; when the +ether evaporated, and the phosphorus began to fume, the solution of +platina was applied to the silk; and, in some time, delicate films of +reduced platina were visible where the water was most abundant. These +films of platina commonly disappear; and nothing remains but a brown +tinge, which, however, is more intense, than what the solution of +platina alone gives the silk. + +To succeed in this experiment, the silk should be replete with +phosphorus; which is easily done by applying the solution twice or +thrice, and waiting after each application, till the fumes begin to +appear. It is also necessary to keep the silk constantly wet with +water. Sometimes it requires from ten to twenty minutes to reduce +platina in this manner. + + +EXP. 17. MERCURY. + +I dipped a bit of silk in a solution of oxygenated muriate of mercury, +and dried it in the air; then the solution of phosphorus was applied; +when the ether evaporated, and the phosphorus began to fume, a yellow +stain commenced on the margin, and gradually appeared over the whole. + +To compare the effects of different degrees of moisture, I immersed a +bit of silk in the same solution of mercury, and dried it carefully at +the fire; the solution of phosphorus was then applied; the silk began +to fume; but no change, except a very slight ring of a yellow hue, +appeared. The rest of the silk retained its white colour. + +Another bit of silk was immersed in the solution of phosphorus, when +the ether evaporated, and the phosphorus began to fume, the same +solution of mercury in distilled water was applied; and, in a few +seconds, a bright film of reduced mercury was visible on the margin of +the part, to which the metallic solution was applied, and after some +time appeared on the whole. The reduction was attended with the colours +of the rainbow. + +After a little time, these colours vanish, and the metallic film +becomes much more obscure, according as the silk dries, and is +succeeded by a yellow stain. + + +EXP. 18. MERCURY. + +A bit of silk was dipped in a solution of nitrate of mercury in +distilled water, and dried at the fire; then the solution of phosphorus +was applied; and, when it began to fume, a brown stain commenced at +the margin, which soon diffused itself over the whole, and gradually +acquired a faint tinge of black. + +Another piece of silk, treated in the same manner, but dried in the +air, exhibited the same appearances; except that the brown tinge verged +more on black. + +Another bit of silk was immersed in the solution of phosphorus, and +when it began to fume, the solution of nitrate of mercury was applied; +a brown colour instantly appeared, accompanied with a film of reduced +mercury, which was most evident where the metallic solution was most +abundant. This film soon disappeared, and was succeeded by a black +stain, in which, however, reduced mercury was visible. No colours but +black, and brown, appeared in this experiment. + +It appears from these experiments on mercury, that the reduction kept +pace with the quantity of water present. + + +EXP. 19. COPPER. + +A piece of silk was immersed in a solution of sulphate of copper, and +dried in the air: then a strong solution of phosphorus was applied; the +silk acquired a brown colour; but no other visible alteration occurred. + +Another piece of silk was dipped in the same solution of copper, and +dried at the fire much better than the preceding; the solution of +phosphorus was applied; when the ether evaporated, and the phosphorus +began to fume, a brown tinge commenced on the margin of the silk, and +gradually diffused itself over the whole; but the stain was by no means +so intense as that produced in the preceding piece: so that there can +be no doubt that the difference was owing to the different degrees of +moisture in the silk. + +After this piece remained in the air for some time, the brown tinge +became more intense, a proof that it attracted water from the air. This +difference in the appearances of pieces dried in the air, and at the +fire, I frequently remarked. + + +EXP. 20. COPPER. + +A strong solution of phosphorus was applied to a piece of silk, when +the ether evaporated, and the phosphorus began to fume, a solution of +sulphate of copper was applied; a brown stain was instantly produced, +and its margins were soon covered with a _white_ metallic film, parts +of which, after some time, verged on the colour of copper, intermixed +with purple, green, and blue. If the solution of phosphorus be weak, +which is always the case, when the ether is bad, nothing appears on +the silk but the brown stain, and the _white_ metallic film. As the +silk dries most of these appearances vanish; but some of the blue tinge +survives; and the silk looks very unseemly. + +A bit of silk was immersed in the same solution of copper, and exposed +to the vapour of phosphorus, as in experiment the 9th; but no change +was produced on the silk, except a few brown spots, though the heat +was such that the vapour filled the phial, and circulated through it: +the vapour corroded a brass pin, which was used to suspend the silk +in the phial. This induced me to try its effects on copper, which +was corroded by it in a remarkable manner, and changed into a black +substance resembling a mixture of charcoal and oil. It appears then +that phosphorus is ill adapted to the reduction of this metal. + + +EXP. 21. TIN. + +A bit of silk was immersed in a solution of muriate of tin in distilled +water, and dried in the air; the solution of phosphorus was then +applied to the silk, and though it fumed considerably, no change +whatever could be perceived in the colour of the silk; nor was there +the smallest appearance of reduction. + +I poured some of the solution of phosphorus on a bit of silk, and when +it began to fume, the solution of tin was applied: after a few seconds, +white metallic films appeared, first on the margin, and were gradually +diffused over that part of the silk, to which the muriate of tin was +applied: a yellow colour intermixed with red sometimes attends the +reduction. After some little time these films of reduced tin vanish, +and scarcely leave a stain behind. + +I did not succeed in reducing acetite of lead, muriate of arsenic, or +sulphates of iron, and zinc, in this way. + +These experiments on tin shew that water is essential to its reduction +by phosphorus, and give additional force to the preceding conclusions. + +M. Sage discovered that gold, silver, &c. are precipitated from their +solutions in the metallic form, by pieces of phosphorus, which are +covered at the same time with bright coats of gold, silver, &c. + +To determine if water were essential to these reductions performed by +M. Sage, I made the following experiments. + + +EXP. 22. GOLD. + +Some solution of phosphorus in ether was poured into a china cup, and +a few drops of the ethereal solution of gold were added; instantly a +brown powder was precipitated similar to what appeared in experiment +the 6th, but no gold in its metallic form could be perceived. + + +EXP. 23. GOLD. + +A solution of nitro-muriate of gold in water was poured into a china +cup, containing a solution of phosphorus in ether; instantly the +gold began to assume its metallic splendour, attended with a variety +of colours, as purple, blue, and red, the beauty of which cannot be +described: the quantity of the blue was gradually diminished, and what +remained, was dispersed over the surface in small films, intermixed +with spangles of reduced gold. Most of the blue films were of a +circular figure; some had a central speck of ruby red, and were fringed +with purple; some had a round central speck of a darker blue than the +surrounding parts: and some were of an irregular figure, fringed with +purple, or ruby red. I often observed these blue films assume the real +colour of gold without suffering any intermediate change of colour; +and, I think, I observed the same of one of the largest specks of ruby +red, that appeared in this experiment. All these colours disappeared, +when the reduction was completed. + +The variety of colours, which those films assume, depends on the +different degrees of reduction; that is to say, on the quantity of +oxygen combined with the metal: in proportion as the metal is deprived +of the oxygen, it assumes various colours, which often succeed +each other in a regular order, showing the different stages of the +reduction: thus when gold is reduced; the first perceptible change is a +green, which soon becomes olive; this is succeeded by blue, and purple; +and sometimes by a ruby red: the purple tinge is a mixture of blue, and +red. + +The various colours, which metals, and their calces, communicate to +glass, and other substances, are explicable on these principles: and +the difficulty of obtaining a ruby-coloured glass by gold is readily +understood from the facility, with which that metal parts with oxygen. + + +EXP. 24. GOLD. + +A thread was passed by means of a needle through a small bit of +phosphorus, which was freed from any moisture, that might adhere to +it, by immersing it for some time in alcohol; it was then suspended +by means of the thread in a solution of gold in ether, contained in +a phial, which was carefully dried in hot sand: in a few minutes, +the solution became turbid, an effervescence commenced, and a brown +precipitate was formed: according as the precipitate fell, the solution +became clear, lost its yellow colour; and the whole of the gold seemed +to have been precipitated: but not a particle of reduced gold could be +seen. + +Another bit of phosphorus was suspended in the same manner in a +solution of nitro-muriate of gold in water; and in a few minutes got a +splendid coat of reduced gold. + + +EXP. 25. SILVER. + +A few drops of a solution of fused nitrate of silver in alcohol were +poured into a china cup containing a solution of phosphorus in ether: +instantly a black precipitate, with a tinge of brown, was formed; but +no silver in its metallic state could be perceived. + +After some time the precipitate attracted moisture from the air; and +some films of reduced silver appeared. + +The same experiment was made in a phial, which was corked, to exclude +the moisture of the air; and nothing, but the black precipitate, +appeared. + +Some of the same solution of silver was diluted with water, and dropped +on a solution of phosphorus in ether; and instantly films of reduced +silver floated on the surface. + + +EXP. 26. SILVER. + +A bit of phosphorus was suspended by a thread in some of the same +solution of silver in alcohol, contained in a phial carefully dried: a +black precipitate with a tinge of brown soon appeared; but no silver in +its metallic state could be observed; part of the precipitate adhered +to the phosphorus, and part fell to the bottom of the phial. + +In another experiment made in a phial not sufficiently dried, a few +small films of reduced silver were observed on the sides of the phial; +but not a particle of silver in its metallic form could be seen on the +phosphorus. + +Another bit of phosphorus was suspended in a diluted solution of +nitrate of silver in water: and in some hours, the phosphorus was +covered with reduced silver. + +The case of silver, which covered the phosphorus, prevented its +spontaneous combustion in the air; the same was observed of the bit of +phosphorus coated with gold. + +Hence it appears, that M. Sage’s success in reducing metals by +phosphorus depended on the water of the metallic solution. + +These experiments were often repeated with nearly the same result; but +some variety often occurs, depending on various circumstances; as the +strength of the metallic solution, and that of the phosphorus; the +quantity of water present, and the purity of the materials employed. + +It is difficult to obtain ether, or alcohol, with the least possible +quantity of water; and equally difficult to expel all moisture from +the surface of glass; for this reason, the bits of phosphorus in the +experiments made with alcohol and ether were suspended by threads, so +as not to touch the sides of the glass. + +I shall conclude this chapter with a general view of the inferences, +which seem naturally to flow from these experiments with phosphorus. + +1. Water is essential to the reduction of metals by phosphorus; +for these experiments show that the reduction is effected only in +proportion to the quantity of water present. + +2. Phosphorus does not reduce the metals by giving them phlogiston. + +3. Phosphorus does not reduce the metals by uniting with, and +separating, their oxygen. + +How then is the reduction effected? are we not to conclude, that it is +effected by the decomposition of the water, in the following manner? + +The phosphorus attracts the oxygen of the water, while the hydrogen of +the latter unites, in its nascent state, with the oxygen of the metal, +and effects the reduction. + +Hence it follows, that the phosphorus is oxygenated by the oxygen of +the water, while the metal is restored to its combustible state. + +Thus what could never be effected by a single, is readily performed by +a double affinity; which always takes place in preference to a single +affinity, as the experiments of Messrs. Monnet, and Kirwan, mentioned +in the preceding chapter, show. + +It is well known, that phosphorus kept in water acquires an oxygenated +crust, which could not happen without a decomposition of the water: +this fact serves to confirm the explanation here offered. + +And indeed the decomposition of water in these experiments must be +granted, or it must be supposed, that water itself reduces the metals, +by uniting with their earths, and constituting their phlogiston; or by +uniting with, and separating, their oxygen; suppositions repugnant to +our present knowledge of chymistry. + + + + +CHAPTER III. + +_Reduction of Metals by Sulphur._ + + +Though Sulphur, as far as my reading extends, has seldom been +considered as a reducer of the metals, yet as it holds a distinguished +rank among combustible bodies, analogy led me to examine its powers in +reducing and fixing the metals in the fibres of silk. + +The vapour of sulphur appeared to be the most simple form, in which +it could be applied to this purpose; and may be obtained by placing a +phial containing flowers of sulphur in hot sand: as the sulphur melts, +it assumes the form of vapour, which soon fills the phial, expels the +atmospheric air, and bears a considerable heat, before it inflames; a +bit of silk, prepared for the experiment, may be held over the vapour, +as it issues from the phial, or immersed in it. The neck of the phial +should be of a convenient size for this purpose. + +But these experiments are more conveniently made by means of a +sulphurous match, and a glass funnel, in which the silk imbued with the +metallic solution may be suspended by a thread passed through it, and +made fast with a cork, which also serves to confine the vapour. + +The glass is then placed on a table, and by moving it a little beyond +the verge of the same, a lighted match is readily introduced, which, as +soon as the glass is filled with vapour, may be withdrawn; the vapour +is confined by making the glass glide back on the table; and thus the +phenomena of the experiment can be easily observed. + +Though the vapour obtained in this manner be chiefly sulphurous acid +gas; yet its effects are not less interesting on that account. + + +EXP. 1. GOLD. + +A bit of silk was dipped in a solution of gold in ether, and dried: +it was then suspended in the glass funnel, and exposed for some time +to the vapour obtained from a burning match: but no change could be +perceived, except that the silk became a little brown. + +Another bit of silk, prepared in the same manner, was immersed in the +vapour of sulphur, formed in a phial placed in hot sand, with the same +result. + + +EXP. 2. GOLD. + +A piece of silk was immersed in a solution of nitro-muriate of gold in +water, suspended in the glass funnel, and exposed, while wet, to vapour +of sulphur, formed by a burning match; no sooner did the vapour touch +the silk, than the reduction commenced; and in a few seconds the whole +piece was covered with a splendid coat of reduced gold, permanent, and +retentive of its lustre; but had a few specks of a dull violet hue. + +The silk viewed by transmitted light appeared of a beautiful blue +colour; and being removed from the vapour, and suspended in the air, +began in about ten minutes to exhale a vapour, which continued about +two hours, and smelled acid, and pungent. + +Another bit of silk, dipped in the same solution of gold, and dried, +was wetted with alcohol, and exposed to the same vapour: the silk +acquired a brownish hue; and a small white metallic film appeared on +its lower end, where the alcohol most abounded: the silk was then +wetted with water, and replaced in the vapour; instantly a lively +purple with a bright pellicle of reduced gold appeared. + + +EXP. 3. SILVER. + +A piece of silk was immersed in a solution of nitrate of silver in +water, and suspended in the air of a dark closet to dry; the silk +retained its white colour, though it remained in the air twenty-four +hours; it was then exposed fourteen hours to the vapour obtained from a +burning match; but suffered no change, except that it acquired a brown +tinge: it was now wetted with alcohol, and replaced in the vapour for +some time; no signs of reduction appearing, it was wetted again with +the alcohol, and exposed to the vapour; but still no signs of reduction +could be perceived: I then wetted the silk with distilled water, +replaced it in the sulphureous vapour; and in about a minute reduced +silver appeared. + + +EXP. 4. SILVER. + +I dipped a bit of silk in a solution of nitrate of silver in distilled +water, and exposed it, while wet, to the vapour of sulphur, as in the +preceding experiment; in a few seconds the silver appeared in its +metallic form, attended with a variety of lively colours: the most +remarkable of these were a pleasant blue, orange, purple, and yellow, +which soon disappeared: the reduced silver also disappeared in a +great measure, some faint traces only remaining. The silk was removed +from the vapour into the air, but exhaled no vapour, as happened in +experiment the second. + +A small bit of sulphur was suspended in a phial containing a solution +of nitrate of silver in water; and after some weeks the sulphur was +coated with reduced silver of no great lustre. + + +EXP. 5. PLATINA. + +A bit of silk was immersed in a solution of nitro-muriate of the ore +of platina in distilled water, and dried in the air; it was then +suspended in the glass funnel, and exposed to the vapour of a burning +match: but no signs of reduction could be observed: the silk retained +the colour, the solution gave it. + +Another bit of silk was dipped in the same solution of platina, and +exposed, while wet, to the sulphureous vapour; in a few seconds the +reduction was very evident. The silk was immerged in a glass of clear +water, and transferred bright films of reduced platina to the surface +of that fluid; most of them were of the same colour as the spangles +in the ore of platina; and some were distinguished by lively blue and +purple colours. + +Another bit of silk, dipped in the same solution of platina, was +immersed, while wet, in the vapour of sulphur, formed in a phial placed +in hot sand; the reduction soon commenced, and was much more perfect, +and permanent, than in pieces exposed to the vapour obtained from +ignited matches. + +It is remarkable that sulphur reduced this metal much better, than +phosphorus or hydrogen gas did: but the reduced platina disappears +after some time, and leaves nothing behind but a brown stain. + +If the films be transferred from the silk to water, they may be +preserved in their metallic form. + + +EXP. 6. MERCURY. + +A bit of silk was immersed in a solution of nitrate of mercury in +distilled water, and dried; parts of the silk immediately acquired +a slate colour: the silk was then exposed to the vapour of sulphur, +obtained from a burning match; but it suffered no change, except that +the colour became a little more intense. + +Another bit of silk was dipped in the same solution of mercury, and +exposed, while wet, to the same vapour: the reduction instantly +commenced in a very evident manner, accompanied with several colours, +as blue, purple, and yellow. + +The silk was removed from the vapour, and soon lost most of its lustre, +which was succeeded by a slate colour, through which some particles of +reduced mercury were observed to shine. + + +EXP. 7. MERCURY. + +A bit of silk was immersed in a solution of oxygenated muriate of +mercury in water, and dried in the air: it was then exposed to the +sulphureous vapour obtained from a burning match; but the silk +underwent no visible change. This solution of mercury does not change +the white colour of silk, as that of nitrate does. + +Another bit of silk was dipped in the same solution of oxygenated +muriate of mercury, and exposed, while wet, to the vapour; in a few +seconds reduced mercury appeared, unattended by any colour, except a +slight tinge of citron yellow on part of the silk. After some time the +whole of the reduced mercury vanished. + + +EXP. 8. COPPER. + +A piece of silk was immersed in a solution of sulphate of copper, and +dried; it was then suspended in the glass funnel, and exposed to the +vapour obtained from a burning match; but the silk suffered no change, +retaining the colour, which the solution gave it. + +Another bit of silk was dipped in the same solution of copper, and +exposed, while wet, to the vapour of an ignited match; in a short +time a white metallic film appeared, accompanied with a brown tinge; +the silk becoming dry, was wetted with water, and exposed to a brisk +vapour from another match: the film became more evident, and parts of +it verged on yellow, bordering on a copper colour. After some time this +white metallic film disappears, and nothing remains but a light brown +stain. + + +EXP. 9. LEAD. + +A bit of silk was immersed in a solution of acetite of lead in +distilled water, and dried in the air: it was then exposed to the +sulphureous vapour of a burning match; but underwent no visible change +whatever. + +Another bit of silk was dipped in the same solution of lead, and +exposed, while wet, to the vapour; reduced lead soon appeared all over +the silk; but after some time this reduced lead disappears, unless it +be transferred to the surface of water. + + +EXP. 10. TIN. + +A bit of silk was immersed in a solution of muriate of tin in distilled +water, and dried in the air: it was then exposed to the vapour obtained +from a burning match, which soon filled the glass; but produced no +visible change on the silk. + +Another bit of silk was dipped in the same solution of tin, and +exposed, while wet, to the sulphureous vapour; and in a few seconds +reduced tin appeared all over the silk; but the tin soon disappears, if +not transferred to water. + + +EXP. 11. ARSENIC. + +A bit of silk was immersed in a solution of muriate of arsenic in +distilled water, and dried in the air; it was then exposed to the +vapour of sulphur, obtained from a burning match; but the silk suffered +no apparent alteration. + +Another bit of silk was dipped in the same solution of arsenic, and +exposed, while wet, to the vapour: in a few seconds the arsenic was +reduced, but not in a very evident manner; the silk was immerged in +water, and several bright films of reduced arsenic floated on the +surface of that fluid. + + +EXP. 12. BISMUTH. + +A bit of silk was immersed in a solution of nitrate of bismuth in +distilled water, and dried in the air; it was then exposed to the +vapour of sulphur obtained from a burning match; but no signs of +reduction appeared. + +Another bit of silk was dipped in the same solution of bismuth, and +exposed, while wet, to the sulphureous vapour; the bismuth was soon +reduced, accompanied with a brown stain: but the metallic lustre soon +disappeared. + + +EXP. 13. ANTIMONY. + +A piece of silk was immersed in a solution of tartarite of antimony in +water, and dried; it was then exposed to the vapour of a burning match; +but no change could be observed; nor did the silk immerged in water +deposit any films on its surface. + +Another piece of silk was dipped in the same solution of antimony, and +exposed, while wet, to the vapour: the silk, in a few seconds, acquired +a yellow colour, and a bright bluish film of reduced antimony appeared +on the lower end of the silk, where the water was most abundant: the +silk was then immerged in a glass of water, and transferred a large +pellicle of reduced antimony to the surface of that fluid. + + +EXP. 14. IRON. + +A bit of silk was immersed in a largely diluted solution of sulphate of +iron in distilled water, and dried in the air; it was then exposed to +the vapour of sulphur obtained from a burning match; after some time +the colour of the silk became a little brown; but no reduced iron could +be seen; nor did the silk immerged in a glass of clear water transfer +any thing metallic to its surface. + +Another bit of silk was dipped in the same solution of iron, and +exposed, while wet, to the sulphureous vapour; in a short time the silk +was withdrawn, and a minute shining film, of a livid white colour, was +visible on its lower margin, where the water most abounded: the silk +was then immerged in a glass of water, and transferred a large film of +reduced iron to its surface. + +This experiment succeeded also with the vapour of sulphur formed in a +phial placed on hot sand. The films of reduced iron were seldom visible +on the silk; but were soon rendered visible, by transferring them to +water. + + +EXP. 15. ZINC. + +A piece of silk was dipped in a diluted solution of sulphate of zinc, +and dried; it was then exposed to the vapour obtained from a burning +match; no change whatever could be perceived: the silk was immerged in +a glass of water, but deposited no film on its surface. + +Another piece of silk was dipped in the same solution of zinc, and +immersed while wet in the vapour of sulphur formed in a phial placed +on hot sand; in about half a minute the silk was withdrawn from the +vapour, and some parts of it had a shining livid appearance, which I +took for reduced zinc: in order to determine if the reduction were +real, the silk was immerged in a glass of clear water, and transferred +to its surface a bright film of reduced zinc. + +If the silk be kept too long in the vapour, some sulphur will be +condensed on its surface, and give it a yellow colour: if it be then +dipped in a glass of water, it will deposit both the sulphur, and +the metallic films on its surface; but the appearance of the sulphur +is so different from that of the reduced metal, that they are easily +distinguished. + +Another bit of silk was immersed in a largely diluted solution of +muriate of zinc, and exposed, while wet, to the vapour obtained from a +burning match: the silk being withdrawn exhibited a few minute shining +films on its lower end, and on immersion in water, left bright films of +reduced zinc floating on the surface of that fluid. + +Very often these films cannot be seen, until they are transferred to +water, which I found a very useful test in doubtful cases: they are +better seen in the gray light than in sunshine. + +These experiments on the reduction of metals by sulphur were often +repeated with nearly the same result: but some variety occurs depending +on the quantity of water present, the strength of the metallic +solution, and sulphureous vapour, and also on the time the silk is +exposed to the vapour. + +When the experiments are made in a phial placed in hot sand, part of +the metallic solution frequently drops from the silk, and falling on +the bottom, or sides of the phial, is reduced, covering these parts +with a metallic crust; on which the sulphur soon reacts, and changes +the greater part into a sulphure. The phial commonly cracks. + +The following conclusions are deducible from the experiments related in +this chapter. + +1. Water is essential to the reduction of metals by sulphur; for this +effect is always in proportion to the quantity of water present. + +2. Alcohol does not promote these reductions without the aid of water. + +3. Sulphur does not reduce the metals by giving them phlogiston; +nor by uniting with and separating their oxygen; for were either of +these opinions just, the sulphur, so minutely divided by heat, should +reduce metallic solutions in alcohol as effectually as it does metallic +solutions in water. + +When we compare these reductions by sulphur, with those effected by +phosphorus, and consider that water is essential to both; we must +conclude, that the reduction is effected in the same manner, viz. by +the decomposition of water; which may be thus explained. + +The sulphur attracts the oxygen of the water, while the hydrogen of the +latter unites, in its nascent state, to the oxygen of the metal, and +restores it to the metallic form. + +Hence it follows, that the sulphur is oxygenated by the oxygen of the +water, while the metal is restored to its combustible state. + +It also follows, that a quantity of water equal to that consumed is +formed by the hydrogen of the water, and the oxygen of the metal. + +This explanation is supported by a fine experiment of Dr. Priestley, +who obtained inflammable air by passing the vapour of water through +sulphur heated in an earthen tube[15]; and farther confirmed by the +experience of some judicious makers of oil of vitriol, who always +sprinkle the sulphur with a certain proportion of water, before they +inflame it. + +The decomposition of water in these reductions must be granted, or it +must be supposed, that a single takes place in preference to a double +affinity; which cannot be admitted. + +These experiments point out several errors in M. Lavoisier’s Table of +the Affinities of the Oxygenous Principle; for he has placed sulphur +at a much greater distance from that principle than any of the metals +treated of in this chapter, except gold; and even in this instance his +table is erroneous, unless it be proved, that sulphur reduces metals +by directly uniting with, and separating their oxygen; a supposition +which implies, that the reduction is effected by a single affinity; and +therefore inadmissible. + +I shall close this chapter with a short extract from the chemical +essays of Bishop Watson; as it seems to have some relation to the +experiments related here. + +His lordship says, that his experiments on “the Derbyshire lead ore +instruct us to believe, that the lead in this kind of ore is in its +metallic state; as the ore was changed into lead without the addition +of any substance containing the inflammable principle[16].” + +But the reduction of lead by sulphur and water, related in this +chapter, points out an evident source of the inflammable principle; +for the ore itself must contain some water, a constituent part of +which is hydrogen, or the base of inflammable air: beside his lordship +thinks, no appearance of lead would have taken place, had there been no +communication with the external air: but as air always holds water in +solution, an ample source of the inflammable principle is evident. + + + + +CHAPTER IV. + +_Reduction of Metals by Alkaline Sulphure._ + + +The Sulphure, I made use of, was prepared by fusing equal parts of +carbonate of potash, and flowers of sulphur, till the effervescence +ceased. + +M. Gengembre has made a very important observation on alkaline +sulphure, prepared in this way, which is, that this substance has no +smell, and that it exhales no gas, while it continues dry; but that, +when it is dissolved in water, or attracts humidity from the air, it +diffuses an offensive smell. + +From this circumstance M. Gengembre inferred, that the disengagement of +this gas depended on the decomposition of water; for he discovered both +by analysis, and synthesis, that this air consists of hydrogen, one of +the principles of water, combined with sulphur, and caloric. + +There can then be no doubt, but alkaline sulphure has the power of +decomposing water; and may therefore be happily employed to illustrate +the mode of action of sulphur, and other combustible substances, +treated of in this essay. + +When dilated acids are poured on solid alkaline sulphure, the +decomposition of the water is promoted, and accelerated, sulphurated +hydrogen gas being formed in great abundance. + +I made two solutions of this alkaline sulphure, one in water, and the +other in alcohol. + + +EXP. 1. GOLD. + +A bit of silk was immersed in the solution of sulphure in alcohol, and +then a solution of gold in ether was applied: a brown matter was formed +in the silk; but no reduced gold could be perceived. + +Another bit of silk was dipped in the same solution of sulphure in +alcohol, and a solution of nitro-muriate of gold in water was applied; +a white metallic film was slowly formed; but no other signs of +reduction were visible. + +This experiment was repeated on another bit of silk, with this +difference, that the solutions of the gold, and sulphure, were both in +water; and the white metallic film was instantly formed, accompanied by +a considerable precipitate of a brown matter. + +It is obvious then, that water accelerates, and is necessary to the +appearance of this film: for when both solutions were in water, it +appeared much sooner. + + +EXP. 2. GOLD. + +A piece of silk was immersed in an aqueous solution of gold, in which +the acid predominated, then a few drops of the aqueous solution of +sulphure were applied: a white pellicle, which looked like silver, was +immediately formed, and the silk got a deep brown colour. + +To another piece of silk, dipped in the same solution of gold, +the solution of sulphure in alcohol was applied, a white metallic +film appeared; but not so evident, or so soon, as in the preceding +experiment, wherein the solution of sulphure in water was used: +beside the film produced by the aqueous solution of sulphure was more +permanent, and the stain, which the silk acquired, was more intense, +than those produced by the solution of sulphure in alcohol. + + +EXP. 3. SILVER. + +I immersed a piece of silk in a solution of the sulphure in alcohol, +and after most of the spirit evaporated, a solution of nitrate of +silver in alcohol was applied: nothing appeared on the silk, but a +brown stain. The nitrate of silver, used in this experiment, was fused, +to expel as much water as possible. + +Another piece of silk was dipped in the same solution of sulphure; when +most of the alcohol evaporated, a solution of crystallized nitrate of +silver in water was applied to the silk; and instantly the metallic +lustre of the silver appeared, attended with a brown stain. + + +EXP. 4. SILVER. + +A piece of silk was dipped in the solution of alkaline sulphure in +water, and an aqueous solution of crystallized nitrate of silver was +applied; the silver was immediately reduced in greater quantity than +in the preceding experiment, in which the alkaline sulphure employed +was dissolved in alcohol. The stain produced in the silk was also more +intense. + + +EXP. 5. SILVER. + +A bit of silk was immersed in a solution of the sulphure in water, +and then a solution of nitrate of silver in alcohol was applied: but +nothing appeared on the silk, except a brown stain. The nitrate of +silver, used in this experiment, was fused, which deprived it of a +great part of its acid. That this was the circumstance, which prevented +the reduction of the silver, appears from the following experiment. + +A bit of silk was immersed in the same solution of silver in alcohol, +then some diluted nitric acid was applied, lastly the aqueous solution +of sulphure was dropped on the silk: and instantly the silver was +restored to its metallic splendour. It is evident then, that acids +contribute to the reduction of silver by alkaline sulphure, which they +effect by promoting the decomposition of water. + +In some time the reduced silver disappears for the most part: and +indeed the white metallic films, which were produced in the experiments +on gold, totally disappeared. + + +EXP. 6. PLATINA. + +A bit of silk was immersed in a solution of nitro-muriate of the ore of +platina in distilled water, and dried; then the solution of sulphure in +alcohol was dropped on the silk: nothing appeared but a brown stain. + +Another bit of silk was dipped in the aqueous solution of sulphure, and +a little of the solution of platina applied; in a short time, a film of +reduced platina appeared. + +To another bit of silk, which was dipped in the solution of platina, a +few drops of distilled vinegar were applied, and then the solution of +sulphure in water was added; a brown stain was immediately produced, +and more platina reduced than in the preceding experiment. + + +EXP. 7. MERCURY. + +To a bit of silk, which was immersed in a solution of oxygenated +muriate of mercury in water, and dried in the air; some of the solution +of sulphure in alcohol was applied; but no change, except a light +yellowish brown, was produced. + +After the silk was some time exposed to the air, some very faint shades +of black were visible on parts of it. + +To a piece of silk, which was immersed in the solution of sulphure in +water, some of the same solution of mercury was applied; immediately +the metal was restored to its metallic lustre, in a very striking +manner; and it was remarkable, that the precipitate on the silk was +very small. + +This experiment was repeated with this difference, that the silk +was first wetted with distilled vinegar: and more of the mercury +was reduced, than in the preceding experiment, attended with an +olive precipitate, which gradually turned blackish: the quantity +of precipitated matter in this was much greater than in the former +experiment; but the reduced metal was not so bright. + + +EXP. 8. MERCURY. + +A bit of silk, which was dipped in a solution of nitrate of mercury, +and dried in the air, had no change produced on it by a solution of +sulphure in alcohol, except a stain compounded of the slate colour, +which the nitrate imparts, and the yellow of the sulphure. + +To another bit of silk, which was immersed in the aqueous solution of +sulphure, some of the same solution of mercury was applied: the metal +was immediately reduced; and a very black stain attended the reduction. + + +EXP. 9. COPPER. + +A piece of silk was dipped in a solution of sulphate of copper, and +dried in the air; a solution of the sulphure in alcohol was applied to +it; but no change, except a brown stain, was produced. + +To another bit of silk, immersed in the aqueous solution of sulphure, +some of the same solution of copper was applied: a white metallic film +was slowly formed, attended with a brown colour. + +On another bit of silk, which was dipped in the same solution of +copper, and placed on a saucer, some distilled vinegar was dropped, +and then a few drops of the aqueous solution of sulphure were added: +immediately a white metallic film appeared in greater quantity than in +the preceding experiment. + + +EXP. 10. LEAD. + +A piece of silk was immersed in a solution of acetite of lead in +distilled water, and dried in the air; then the solution of sulphure in +alcohol was applied: but nothing appeared on the silk, except a brown +stain. + +A bit of the same silk was dipped in the same solution of lead, then +the solution of sulphure in water was applied: the lead was soon +reduced to its metallic state: a brown stain, and precipitate of the +same colour, attending the reduction. + +The same experiment was repeated with this difference, that the silk +was first wetted with distilled vinegar, and instantly the lead was +reduced of greater lustre, and in greater quantity, than in the +preceding experiment. + +This experiment was tried on a bit of white calico, dipped in distilled +vinegar, and placed on the palm of my hand; and instantly the metallic +lustre of the lead, which was reduced in great quantity, appeared in a +very remarkable manner, attended with a brown stain. + + +EXP. 11. TIN. + +To a bit of silk dipped in a solution of muriate of tin in distilled +water, and dried in the air, the solution of sulphure in alcohol was +applied: nothing appeared but a brown stain. + +Another bit of silk was immersed in the solution of sulphure in water, +then the same solution of muriate of tin was applied; in a short time +some reduced tin appeared on the silk. Vinegar promoted the reduction +of this metal also, in a remarkable manner. + + +EXP. 12. ARSENIC. + +A bit of silk was immersed in a solution of muriate of arsenic in +distilled water, and dried in the air: the solution of sulphure in +alcohol was then applied: the silk first looked yellow, in a short +time the yellow colour almost entirely disappeared, leaving behind a +whitish precipitate; but no other change was produced. + +Another bit of silk was dipped in the solution of sulphure in water; +then some of the same solution of arsenic was applied; a yellow +precipitate was formed; and shortly after, this precipitate was +surrounded by a violet margin; but no other change could be observed. + +I immersed another bit of the same silk in the same solution of +arsenic, some distilled vinegar was then dropped on it; and lastly the +aqueous solution of sulphure was applied: after some time, a few minute +films of reduced arsenic bright as silver were visible. + +Some attention is necessary to discover the reduced arsenic, as the +particles reduced are few, and minute; and sometimes none can be seen. + + +EXP. 13. BISMUTH. + +To a bit of silk, which was dipped in a solution of nitrate of Bismuth +in distilled water, and dried in the air, the solution of sulphure in +alcohol was applied: the silk appeared first yellow, then brown; but no +farther change could be observed. + +Another bit of silk was immersed in the solution of sulphure in water; +some of the same solution of bismuth was then applied to it; the metal +was immediately reduced; and a brown precipitate was formed. Vinegar +seems neither to promote, nor retard the reduction. + +Two bits of white calico were dipped in the same solution of bismuth; +to one of these placed on a saucer some distilled vinegar was added; +then a single drop of the solution of sulphure in water was applied; +and the whole of the calico, except that part on which the drop fell, +was covered with reduced bismuth, which looked exceedingly bright: the +same appearance was observed on the other bit, to which no vinegar was +added. + + +EXP. 14. ANTIMONY. + +To a bit of silk, which was dipped in a solution of tartarite of +antimony in distilled water, and dried in the air, the solution of +sulphure in alcohol was applied; the silk got a yellow colour, whose +margins, some time after, acquired an orange hue; but no other change +was perceived. + +Another bit of the same silk was immersed in the aqueous solution of +sulphure, the same solution of antimony was then applied: part of the +metal was reduced, though in small quantity, attended with an orange +precipitate. + +The acids of vinegar, and tartar, seemed to impede the reduction; the +muriatic acid also seemed to have the same effect, though not in so +great a degree as the two former. + + +EXP. 15. COBALT. + +To a bit of silk, which was dipped in a solution of nitrate of cobalt, +and dried in the air, the solution of sulphure in alcohol was applied; +the silk soon became brown; but no farther change could be perceived. + +To another bit of silk, which was immersed in the solution of sulphure +in water, a few drops of the same solution of cobalt were applied: the +silk immediately acquired a dark colour, and, in a little time, some +of the metal was reduced, attended with a dull blue precipitate, which +changed to a blackish brown. + +Muriate of cobalt was reduced in the same manner: vinegar promoted the +reduction of both these preparations of cobalt. + +EXP. 16. IRON. + +To a piece of silk, which was immersed in a solution of sulphate of +iron largely diluted, and dried in the air, the solution of sulphure in +alcohol was applied: the silk soon became black; but no other change +could be perceived. + +Another bit of silk was dipped in the solution of sulphure in water, +some of the same solution of iron was then applied: the silk instantly +assumed a black colour; but no reduced iron appearing, it was immerged +in a glass of water, and transferred a bright film of reduced iron to +the surface of that fluid. + +Sometimes part of the film has not the metallic lustre, which is very +evident in other parts of it; so that the parts completely reduced can +be easily distinguished from the dull and imperfectly reduced black +oxid of iron, intermixed with these bright films. + +The same experiments were repeated on bits of calico with the same +result: the calico from its spongy texture is better suited to produce +strong films than silk is. + +Vinegar did not promote the reduction of iron in these experiments. + + +EXP. 17. ZINC. + +To a bit of silk, which was immersed in a largely diluted solution of +muriate of zinc, and dried in the air, some of the solution of sulphure +in alcohol was applied; nothing appeared on the silk, but the yellow +colour, which the solution of sulphure imparts. + +Another bit of silk was dipped in the solution of sulphure in water, +and some of the same solution of zinc was applied: the yellow colour, +which the solution of sulphure gave the silk, soon became white; but +no reduced zinc could be seen. The silk was then immerged in a glass +of clear water, and transferred a bright film of reduced zinc to its +surface. + +In another experiment, made with white calico, the pellicle transferred +to the surface of water was brighter; and more zinc was reduced, than +in the preceding experiment. + +Sulphate of zinc also was reduced both on silk, and calico, with this +difference that black, and olive, precipitates, attended the reduction. + + +EXP. 18. MANGANESE. + +I dipped a bit of silk in a diluted solution of nitrate of manganese, +and dried it in the air; the solution of sulphure in alcohol was then +applied: the silk acquired a yellow colour, which soon disappeared; but +no other change could be observed. + +To another bit of silk, which was immersed in the solution of sulphure +in water, a drop of the same solution of manganese was applied: +instantly a pearl-white precipitate was formed, the margin of which +soon acquired a bright film of reduced manganese. Under this film a +violet tinge was evident. + +The nitrate of manganese used in this experiment was very acid. + +A solution of alkaline sulphure in water after a certain length of time +loses the power of reducing the metals, in which respect it resembles +an old solution of sulphate of iron. + +Having procured a more neutral solution of nitrate of manganese, I +immersed a bit of silk in the solution of sulphure in alcohol, when +most of the spirit evaporated; a single drop of this solution of +manganese was applied; instantly a bright film of reduced manganese +appeared, attended with a violet tinge, and a brown precipitate. After +some time the violet tinge disappears. + +On another bit of silk immersed in the same solution of sulphure in +alcohol, a drop of a solution of sulphate of manganese in distilled +water was applied: instantly films of reduced manganese bright +as silver appeared, accompanied with a faint violet tinge, and a +pearl-white precipitate. These films soon disappear. + +A solution of alkaline sulphure in alcohol does not by age lose its +power of reducing the metals, as that in water does; I kept the former +solution more than two years, and found it, at the end of that time, as +capable of reducing the metals, as when it was made. + +It is manifest from the experiments related in this chapter, + +1. That water is essential to the reduction of metals by alkaline +sulphure. + +2. That alcohol does not promote these reductions, without the aid of +water. + +3. That alkaline sulphure does not reduce the metals by giving them +phlogiston; nor by uniting with, and separating, their oxygen; for +were either of these opinions true, a solution of alkaline sulphure in +alcohol should reduce them as effectually, as a solution of the same in +water does. + +4. That acids contribute to these reductions by promoting the +decomposition of water. + +Now since M. Gengembre has demonstrated, that water is decomposed +by alkaline sulphure; who can doubt, that it is decomposed in these +reductions? + +The manner, in which metals are reduced by this substance, seems to be +the following. + +An hydrure of sulphur, that is, a combination of hydrogen, and sulphur, +is formed: this hydrure of sulphur attracts the oxygen of the water, +while the hydrogen of the latter unites, in its nascent state, with the +oxygen of the metal, and reduces it. + +The experiments in this chapter leave us no room to doubt of the +decomposition of water in metallic reductions by alkaline sulphure, +and serve to illustrate, and confirm, the manner, in which sulphur, +phosphorus, and other combustible bodies, effect the reduction of +metals. + + + + +CHAPTER V. + +REDUCTION OF METALS + +BY + +_SULPHURATED HYDROGEN GAS_. + + +Having treated of the effects of hydrogen gas, and sulphur, separately, +I shall next treat of their effects, when combined in the form of +sulphurated hydrogen gas. + +I obtained this elastic fluid by pouring water, acidulated with +sulphuric acid, on alkaline sulphure, prepared in the manner mentioned +in the preceding chapter; but had it been prepared with a caustic +alkali, it is probable, the gas would be more powerful. The sulphure of +the shops is generally unfit for these experiments. + +It is necessary in experiments with sulphurated hydrogen gas, hydrogen +gas, &c. to have some mode of conveying them into a chimney; as they +are offensive, and unwholesome. + + +EXP. 1. GOLD + +A piece of silk, which was immersed in a solution of nitro-muriate +of gold in water, and dried in the air, was exposed to sulphurated +hydrogen gas: the silk got a slight tinge of brown; but no other +change occurred: it was then wetted with alcohol, and after some time, +the brown became more intense; and white films appeared on some parts +of the silk, owing to moisture collected from the gas, which is always +replete with water. + +Another bit of silk was dipped in the same solution of gold, and +exposed, while wet, to the gas: the yellow colour, which the solution +of gold gave the silk, was immediately changed to a brown; and a white +metallic pellicle appeared, and covered the whole surface of the silk +opposed to the gas; but no purple, or other colours, that usually +attend the reduction of this metal by other agents, could be perceived. +This pellicle did not entirely disappear, as the silk became dry; +though it lost most of its lustre, and looked more like silver, or some +other white metal imperfectly reduced, than gold. + +This elastic fluid, and alkaline sulphure, have an effect on the +reduction of gold, very different from that of the vapour of sulphur, +obtained from a burning match, which further appears from the following +experiment, made with sulphurated hydrogen gas, that happened to be +mixed with some sulphurous acid gas. + + +EXP. 2. GOLD. + +A piece of silk, which was dipped in a solution of gold in ether, and +dried in the air, was exposed to a current of sulphurated hydrogen +gas, containing some sulphurous acid gas; but no signs of reduction +could be perceived: the silk was then wetted with alcohol; still no +visible change was produced, except a brown stain, where the alcohol +most abounded: this stain, after some minutes exposure to atmospheric +air, was covered with a white metallic film, which soon disappeared: +after some minutes, the silk was wetted with water, and exposed again +to the gas; a white metallic film immediately appeared, and the brown +stain began to change slowly to a purple; the silk was soon covered +with various colours, as blue, red, and orange; and some spots of +reduced gold of its own proper colour appeared: after some time the +white film, and all the colours, except the purple, disappeared: some +specks of the perfectly reduced gold were permanent. + +Another bit of silk, which was immersed in an aqueous solution of +gold, and exposed to the same mixed gas, exhibited nearly the same +appearances. + + +EXP. 3. GOLD. + +Having found that sulphurated hydrogen gas had a powerful effect in +reducing other metals, I was desirous of trying its effects on a larger +scale, thinking it might be attended with more success: I therefore +immersed a quarter of a yard of silk in an aqueous solution of gold, +and exposed it, while wet, to this gas in close vessels: the silk was +soon covered with a white metallic pellicle, which disappeared in a +short time: the experiment was continued about twelve hours, and, on +withdrawing the silk from the gas, I could not perceive the smallest +vestige of reduced metal, or purple, or other colours, that constantly +attend the reduction of gold. + +The silk had a dull brown hue verging on a slate colour. + + +EXP. 4. SILVER. + +A piece of silk, which was immersed in a solution of nitrate of silver +in water, and dried in the air, was exposed to a current of sulphurated +hydrogen gas; but no change could be perceived for some time; at +length, when the silk collected moisture from the gas, some particles +of reduced silver were visible, accompanied by a brown stain. + +Another piece of silk was dipped in the same solution of nitrate of +silver, and exposed, while wet, to the gas: the silver was instantly +reduced all over the side of the silk opposed to the current: a great +variety of beautiful colours, as red, orange, yellow, green, and blue, +attended the reduction: most of these disappeared; but part of the +silver remained permanently reduced. + +I found, that, if the silk be immersed in a solution of silver in +alcohol, and dried, and then moistened with water, and exposed, while +wet, to the gas, none of these colours appear. + +This experiment was repeated on a quarter of a yard of silk in close +vessels, and immediately both sides of the silk were covered with +reduced silver, attended with the same beautiful colours: the silk was +left exposed to the gas seven or eight hours; and being then examined, +no reduced silver could be seen: nothing remained, but a strange medley +of colours, chiefly blue, green, purple, and orange, unequally mixed, +some prevailing more than others in certain parts of the silk: however +the die is by no means disagreeable. + + +EXP. 5. SILVER. + +A piece of silk, which was immersed in a solution of fused nitrate of +silver in alcohol, and dried in the air, was exposed to a current of +the gas; but no change could be perceived for some time: it was then +wetted with alcohol, still no alteration could be observed, till the +silk attracted moisture from the gas, when small particles of reduced +silver began to appear, attended with a brown stain. + +If the silk immersed in the solution of silver in alcohol, and exposed +while wet to the gas, be kept constantly wet with alcohol, these +appearances take place sooner. + +A piece of silk, which was dipped in a solution of muriate of silver in +ammonia, and exposed, while wet, to the gas, had in a short time its +surface covered with reduced silver: but another piece of silk dipped +in the same solution of silver, and dried, underwent no such change. + + +EXP. 6. PLATINA. + +A bit of silk, which was dipped in a solution of nitro-muriate of the +ore of platina in distilled water, and dried in the air, was exposed +to a current of sulphurated hydrogen gas; but underwent no perceptible +change. + +Another bit of silk was immersed in the same solution of platina, and +exposed, while wet, to the gas; the whole surface of the silk, opposed +to the current, was instantly covered with reduced platina, which soon +lost its lustre; nothing remaining but a brown colour, with some faint +vestiges of the reduced metal. + +This experiment was repeated on a bit of linen with the same result. + + +EXP. 7. MERCURY. + +A bit of silk, which was dipped in a solution of oxygenated muriate +of mercury in distilled water, and dried in the air, was exposed to a +current of the gas; the only visible change produced was a slight shade +of yellow on part of the silk. + +Another bit of silk was immersed in the same solution of mercury, and +exposed, while wet, to the gas: the mercury was immediately reduced; +but soon lost its lustre: the gas reacting changed most of it to a +substance of a dull white colour. + +The same experiments were made with nitrate of mercury, with the same +result. + + +EXP. 8. COPPER. + +A bit of silk was immersed in a solution of sulphate of copper in +distilled water, and suspended in the air to dry; it was then exposed +to a current of the gas: the silk assumed a brown colour; but no other +change appeared. + +Another bit of silk was dipped in the same solution of copper, and +exposed, while wet, to the gas: a white metallic film, attended with +a brown stain, immediately appeared: some parts had a yellow film +approaching to the colour of copper: these films all disappeared, +leaving behind a brown stain: the parts, which were covered with the +yellow film, resembling copper, exhibited, after some time, a dull +bluish disagreeable matter. + + +EXP. 9. LEAD. + +Having dipped a piece of silk in a solution of acetite of lead in +distilled water, and dried it in the air, I exposed it to a stream of +the gas: the silk became a little brown; but no other change could be +observed. + +Another bit of silk was immersed in the same solution of lead, and +exposed while wet to the gas; no sooner did it touch the silk, than +a brown tinge diffused itself, like a passing shadow, over the whole +surface of the silk, accompanied with a bright coat of reduced lead, +which resembled silver. + +The brown tinge, which the silk acquires, resembles what happens when +white paper is slightly singed by holding it near a burning body. + +This experiment was repeated on a quarter of a yard of silk in close +vessels; and the silk was immediately covered with a coat of reduced +lead, which had the brilliance of silver, and was attended with a brown +tinge: the experiment was continued several hours, after which the +silk was examined, and found to have lost all the argentine lustre, +which was succeeded by a sparkling gray die: a sulphure of lead, or +galena, being formed in the fibres of the silk. The same experiment was +repeated on two other pieces of silk with the same result. + +This elastic fluid is so powerful a reducer of the metals, that if +chambers, painted with white lead, have any considerable degree of +moisture, and are exposed to its influence, the lead on the surface +of the walls is reduced, and that chiefly where the humidity is most +abundant: this effect, I observed, was produced, even at the distance +of three chambers from the place, where the gas was formed: and the +lead was reduced most evidently behind the window-shutters where the +moisture of the wall was most considerable. + +It is a common experiment with chymists, in order to show the effects +of this gas, to draw characters with a solution of sugar of lead on +paper, which they place over a glass of water, containing some alkaline +sulphure: in some time the characters drawn on the paper acquire a +brown, or black colour, and become visible; which amuses the spectators. + +But it is surprising, that the metal has never been reduced in this +experiment even by chance; and not less so, why _lead_ should be +singled out for this trial of skill, in preference to other metals, +which are equally affected by this gas. + + +EXP. 10. TIN. + +A piece of silk was dipped in a solution of muriate of tin in distilled +water, and dried in the air; the silk, on exposure to a current of the +gas, scarce underwent any change, except a few brown specks dispersed +over its surface. + +Another bit of silk was immersed in the same solution of tin, and +exposed, while wet, to the gas, which no sooner touched the silk, than +the surface opposed to the current was covered with reduced tin of +great brightness: in some time various colours, as blue, orange, and +a faint purple, appeared, and became more evident, as the reduction +proceeded. + +The gas does not react on this metal so much as on mercury, and some +other metals: part of the reduced tin remained permanent; but most of +it disappeared, and left behind a disagreeable brown stain. + + +EXP. 11. ARSENIC. + +A bit of silk was immersed in a solution of muriate of arsenic in +distilled water, and dried in the air; it was then exposed to a stream +of sulphurated hydrogen gas; but no change could be observed, except a +faint tinge of citron yellow, which appeared on some parts of the silk. + +Another bit of silk was dipped in the same solution of arsenic, and +exposed, while wet, to the gas: the arsenic was instantly reduced all +over the surface, opposed to the gas, attended with a citron yellow +colour. + +The gas soon reacted on the reduced arsenic; and nothing remained but +the yellow stain. + + +EXP. 12. BISMUTH. + +I dissolved some bismuth in nitric acid, and evaporated the solution +to dryness; the salt was then dissolved in distilled water, and the +solution deposited a copious white precipitate, but retained a quantity +of the metal sufficient for these experiments. + +In this solution of bismuth a piece of silk was immersed, and dried +in the air; it was then exposed to a stream of the gas: and the only +visible effect produced was a very faint tinge of brown. + +Another bit of silk was dipped in the same solution of bismuth, and +exposed wet to the gas: the silk was instantly covered with a bright +pellicle of reduced bismuth, which soon lost most of its metallic +lustre, being changed by the reaction of the gas to a sulphure. + +Mr. Kirwan in his experiments on hepatic air, found, that nitrous +solution of bismuth, by mixture with a solution of hepatic air in +water, changes to a reddish brown, and even assumes a metallic +appearance. + +He also found that nitrates of silver, lead, and acetite of lead, were +precipitated black. + + +EXP. 13. ANTIMONY. + +A piece of silk, which was immersed in a solution of tartarite of +antimony in distilled water, and dried in the air, was exposed to a +stream of the gas; but suffered no visible change, except that a few +specks of yellow, and orange appeared. + +A bit of silk was dipped in the same solution of antimony, and exposed, +while wet, to the gas; the antimony was immediately reduced to its +metallic form, attended with a deep orange colour: in some time, most +of the metallic lustre disappeared, a few specks only remaining +permanent. + + +EXP. 14. IRON. + +A piece of silk was immersed in a diluted solution of sulphate of iron +in distilled water, and dried; it was then exposed to a current of the +gas; but underwent no visible change. + +Another bit of silk was dipped in the same solution of iron, and +exposed, while wet, to the gas: the silk soon began to acquire a dark +colour, which gradually increased, and, at length, became black, +attended with an obscure metallic film. The silk was immersed in water, +and deposited a bright metallic film on the surface of that fluid. + + +EXP. 15. ZINC. + +A bit of silk, which was immersed in a diluted solution of sulphate of +zinc in distilled water, and dried in the air, was exposed to a current +of the gas; but underwent no visible change. + +Another bit of silk was dipped in the same solution of zinc, and +exposed, while wet, to the gas; but no change in the colour of the +silk, or sign of reduction could be perceived: the silk was then +immerged in a glass of clear water, and transferred to its surface a +bright metallic film of the colour of zinc. + +When a languid stream of gas was employed in these experiments, the +films transferred to water were scarce visible. + + +EXP. 16. ZINC. + +A piece of silk, which was immersed in a largely diluted solution of +muriate of zinc, and dried in the air, was exposed to a brisk current +of sulphurated hydrogen gas; but underwent no visible alteration. + +Another bit of silk was dipped in the same solution of zinc, and +exposed, while wet, to the same brisk current of gas; instantly the +surface of the silk, opposed to the gas, was covered with a bright coat +of reduced zinc, attended with faint orange, and purple colours. + +Though the reduced zinc was quite evident; yet I had the curiosity to +examine its appearance on the surface of water; I therefore immersed +the silk in a glass of that fluid, and a bright metallic pellicle, +which retained the texture of the silk, as wax retains the impression +of a seal, was transferred to its surface. + +Another bit of silk, dipped in the same solution of zinc, and exposed +for a longer time to the gas, lost its metallic lustre, the zinc being +changed to a sulphure by the reaction of the gas. + +These experiments on sulphate, and muriate of zinc, show, that the +acid, in which the metal is dissolved, influences the reduction in a +remarkable manner. + +It is evident from the experiments related in this chapter, + +1. That water is essential to the reduction of metals by sulphurated +hydrogen gas. + +2. That alcohol does not promote these reductions, without the aid of +water. + +3. That sulphurated hydrogen gas does not reduce the metals by giving +them phlogiston; nor by uniting with, and separating, their oxygen: +for were either of these opinions well founded; metallic solutions +in alcohol should be as effectually reduced by this gas, as metallic +solutions in water are. + +When we consider, that alkaline sulphure reduces the metals by +decomposing water; we have every reason to conclude, that sulphurated +hydrogen gas reduces them in the same manner; since the same +circumstances are necessary to both: the hydrure of sulphur, which +constitutes the base of this gas, attracts the oxygen of the water, +while the hydrogen of the latter unites, in its nascent state, with the +oxygen of the metal, and reduces it. + +Hence it follows, that the hydrure of sulphur is oxygenated by the +oxygen of the water, while the metal is restored to its combustible +state. + + + + +CHAPTER VI. + +REDUCTION OF METALS + +BY + +_PHOSPHORATED HYDROGEN GAS_. + + +The effects of hydrogen gas and phosphorus on the reduction of metals +in the fibres of silk have been treated of separately in the two +first chapters; in this, I shall briefly treat of their effects, when +combined in the form of phosphorated hydrogen gas, which from its high +degree of inflammability seemed well adapted to this purpose. + +The spontaneous inflammation of this kind of air was known to M. +Gengembre in 1783; and his experiments were published in Rosier’s +journal for October 1785. + +Mr. Kirwan also, without any knowledge of M. Gengembre’s experiments, +discovered the same air, which he calls phosphoric air, and published +his experiments in the 76th volume of the Philosophical Transactions +for 1786. + +This elastic fluid may be obtained by digesting a solution of potash in +water with about half its weight of phosphorus in a heat sufficient to +melt the latter; and may be received in glass vessels over mercury. + +But finding it inconvenient to introduce pieces of silk prepared for +these experiments over mercury in close vessels, I exposed them to the +gas, as it issued from the neck of the phial in which it was prepared. + +Part of this elastic fluid is spontaneously inflammable; but the other +has not that property, which M. Gengembre imputes to the presence of +carbonic acid; for the sake of brevity, I shall design the latter by +the term _gas_, or _phosphorated hydrogen gas_; and the former by the +epithets _spontaneously inflammable_, or _detonating_ gas, which, I +found, does not burn or scorch silk wetted with metallic solutions. + + +EXP. 1. GOLD. + +A piece of silk, which was immersed in a solution of nitro-muriate of +gold in distilled water, and suspended in the air twelve hours to dry, +was divided into three parts. + +One of these was exposed to a stream of phosphorated hydrogen gas: the +silk became brown, and its margins, which happened to touch the sides +of the phial, acquired a violet tinge: but no reduction took place. + +Another of these parts was wetted with alcohol, and exposed to the gas; +but no signs of reduction could be perceived. + +The remaining part was wetted with water, and was no sooner exposed to +the gas, than the reduction commenced over the whole silk, which was +soon covered with a bright coat of reduced gold. + + +EXP. 2. SILVER. + +A piece of silk was dipped in a solution of fused nitrate of silver in +alcohol, and dried in the air: it was then divided into three parts. + +One of these, in order to dissipate moisture more effectually, was +dried still better by a gentle heat, and exposed to the gas; the silk +acquired a brownish dark colour: but no other alteration could be +perceived. + +Another of these parts, which was also better dried by a gentle heat, +was wetted with alcohol, and exposed to the gas: the silk acquired a +dark brown colour; but no other change could be observed. + +The remaining part was wetted with water, and exposed to the gas: the +reduction commenced immediately, and in a short time the silk was +covered with reduced silver. + + +EXP. 3. PLATINA. + +A piece of silk was immersed in a solution of nitro-muriate of the +ore of platina in distilled water, and dried in the air; it was then +divided into three parts. + +One of these parts was exposed to the gas; but suffered no visible +change. + +Another of them was wetted with alcohol, and exposed to the gas; but +underwent no perceptible change. + +The remaining part was wetted with water, and exposed to the gas: in +about three or four minutes, a bright metallic film, of great lustre, +appeared on the side of the silk, opposed to the gas. + +Another bit of silk, which was dipped in the same solution of platina, +and exposed, while wet, to the spontaneously inflammable gas, was +immediately covered with reduced platina, which being transferred +to the surface of water looked bright as silver, and retained the +impression of the silk. + + +EXP. 4. MERCURY. + +A bit of silk, which was immersed in a solution of nitrate of mercury +in distilled water, and dried in the air, was exposed to the gas; but +underwent no visible change. + +Another bit of silk was dipped in the same solution of mercury, and +dried: it was then wetted with alcohol, and exposed to the gas; but no +sign of reduction appeared. + +Another bit of silk was immersed in the same solution of mercury, and +exposed to the gas; the metal was instantly reduced all over the silk; +a great variety of beautiful colours attending. + +A piece of silk was dipped in a solution of oxygenated muriate of +mercury in distilled water, and dried in the air: it was then divided +into two parts. + +One of these was exposed to the gas: no change appearing, it was wetted +with alcohol, and exposed again to the gas; but still no alteration +could be perceived. + +The remaining part was wetted with water, and was no sooner exposed to +the gas, than the mercury was reduced over the whole silk. No colours +attended the reduction. + +Mr. Kirwan introduced some precipitate per se to a small portion of +phosphoric air: the precipitate soon grew black; and a white smoke +appeared; in two days the precipitate remained solid; yet acquired a +pale white colour, like that of steel: the air lost its spontaneous +inflammability[17]. + + +EXP. 5. COPPER. + +A piece of silk, which was immersed in a solution of sulphate of copper +in distilled water, and dried in the air, was divided into two parts. + +One of these was exposed to the gas; but no visible change occurred. + +The remaining part was wetted with water, and exposed to the gas: in +a few minutes a brownish matter appeared in the silk; but nothing +metallic could be seen: the silk was then dipped in a glass of clear +water, and transferred a small white metallic pellicle to its surface. + +In another experiment, made with the spontaneously inflammable gas, +a white metallic pellicle was immediately formed, attended with a +brown stain; this pellicle resembled silver, or a white metal: but the +gas soon reacted on it, and formed a disagreeable brown matter in the +fibres of the silk. + + +EXP. 6. LEAD. + +A bit of silk, which was dipped in a solution of acetite of lead in +distilled water, and dried in the air, was exposed to the gas; but +suffered no visible change. + +Another bit of silk was immersed in the same solution of lead, and +exposed, while wet, to the gas; but nothing metallic could be seen: the +silk, however, on immersion in water, transferred a few minute bright +films to the surface of that fluid. + +In another experiment, made with the detonating gas, the reduced films +were more evident. + + +EXP. 7. TIN. + +A bit of silk, which was dipped in a solution of muriate of tin in +distilled water, and dried in the air, was exposed to the action of the +gas, without suffering any visible alteration. + +Another piece of silk was immersed in the same solution of tin, and +exposed, while wet, to the gas; but no signs of reduction could be +perceived: the silk was then immersed in water, and transferred a +delicate metallic film to its surface. + + +EXP. 8. ARSENIC. + +A bit of silk, which was immersed in a solution of muriate of arsenic +in distilled water, and dried in the air, was exposed to the gas; but +no change could be perceived. + +Another bit of silk, immersed in the same solution of arsenic, and +exposed, while wet, to the gas, acquired in a few minutes a brown +stain; but nothing metallic could be seen on the silk; which, however, +on being dipped in water, transferred a very minute film of reduced +arsenic to its surface. + +In another experiment, made with the detonating gas, the films of +reduced arsenic were much more evident, of greater brilliance, and +attended with a brown stain produced in the fibres of the silk. + + +EXP. 9. BISMUTH. + +A piece of silk, which was dipped in a solution of nitrate of bismuth +in distilled water, and dried in the air, was exposed to the gas; but +no alteration could be observed. + +Another bit of silk was immersed in the same solution of bismuth, and +exposed, while wet, to the gas: the silk in two or three minutes got a +brown stain, which gradually became more intense; and a very delicate +metallic film appeared: the silk was then immerged in water, and +transferred a bright film of reduced bismuth to the surface of that +fluid: the film retained the impression of the silk. + + +EXP. 10. ANTIMONY. + +A bit of silk, immersed in a solution of tartarite of antimony in +distilled water, and dried in the air, was exposed to the gas; but +suffered no apparent change. + +Another piece of silk was dipped in the same solution of antimony, and +exposed, while wet, to the gas; but no signs of reduction appeared: +the silk was then immerged in water, to the surface of which, it +transferred one small spangle. + +This experiment was repeated with the detonating gas, which with +difficulty produced some sparkling films: the silk was immersed in +water, and transferred the films to its surface. + +A white matter was visible in the fibres of the silk. + + +EXP. 11. COBALT. + +A piece of silk, immersed in a solution of muriate of cobalt, and dried +in the air, was exposed to the gas; but suffered no visible alteration. + +Another bit of silk was dipped in the same solution of cobalt, and +exposed, while wet, to the gas: but no sign of reduction appeared; nor +did the silk transfer a film to water. + +Another bit of silk was immersed in a solution of nitrate of cobalt, +and exposed, while wet, to the detonating gas: no signs of reduction +were visible for some time; but at length a few small spangles of +the metal appeared on the silk, and were very brilliant, and when +transferred to water, were still more so: a white matter could be seen +in the fibres of the silk. + + +EXP. 12. IRON. + +A bit of silk was immersed in a largely diluted solution of sulphate of +iron in distilled water, and dried: it was then exposed to the action +of the gas; but no alteration could be perceived. + +Another bit of silk was dipped in the same solution of iron, and +exposed, while wet, to the gas: in a few minutes some parts of the silk +acquired a light brown colour; but no reduced iron could be seen on the +silk, which however transferred a very minute, and delicate film to +water. + +This experiment was repeated with a strong detonating gas, and a very +brilliant metallic film about four lines in diameter was reduced on the +silk accompanied with a brown stain: but nothing like the black oxid of +iron appeared. + + +EXP. 13. ZINC. + +A bit of silk, which was immersed in a largely diluted solution of +muriate of zinc, was exposed dry to the gas; but underwent no visible +alteration. + +Another piece of silk was dipped in the same solution of zinc, and +exposed wet to the gas; no signs of reduction appearing, the silk was +immerged in water, and left a very minute metallic film on its surface, +which could with difficulty be seen. + +The experiment was repeated with the detonating gas, and a very bright +metallic film of zinc, four or five lines in diameter, was reduced on +the silk. + +This experiment succeeded also with a largely diluted solution of +sulphate of zinc. + +The silk, viewed by transmitted light, exhibited a brown stain beneath +these films of iron and zinc. + +The experiments detailed in this chapter show, + +1. That water is essential to the reduction of metals by phosphorated +hydrogen gas. + +2. That alcohol does not promote these reductions, without the aid of +water. + +3. That this elastic fluid does not reduce metals by giving them +phlogiston; nor by combining with, and separating, their oxygen; for +were either of these suppositions true, it should reduce them as well +with alcohol, as with water. + +After explaining the manner, in which sulphurated hydrogen gas reduces +the metals; the mode of agency of phosphorated hydrogen gas is +sufficiently obvious. + +The gas attracts the oxygen of the water, while the hydrogen of the +latter unites, in its nascent state, with the oxygen of the metal, and +reduces it. + +Hence it follows, that the hydrure of phosphorus, which constitutes the +base of this gas, is oxygenated by the oxygen of the water, while the +metal is, at the same time, restored to its combustible state. + +By hydrure of phosphorus is meant, a combination of hydrogen and +phosphorus, containing less caloric, than is necessary to the gazeous +state. + + + + +CHAPTER VII. + +REDUCTION OF METALS + +BY + +_CHARCOAL_. + + +Finding several combustible bodies, as hydrogen, phosphorus, sulphur, +and combinations of these, capable of reducing the metals in the +ordinary temperature of the atmosphere; I was desirous of knowing, if +Charcoal also possessed that power. + +Charcoal may be applied with this view in several forms. M. Rouelle has +observed that caustic fixed alkali dissolves a considerable quantity of +this substance. + +Charcoal also exists in a very attenuated state in ether, alcohol, gum, +&c. + +I have examined some of its effects on the reduction of metals, in +these different forms, in which it probably exists combined with +hydrogen, and also some of its effects in the solid form. + + +EXP. 1. GOLD. + +A small bit of well burned charcoal was suspended by a thread in +a phial containing a diluted solution of nitro-muriate of gold in +distilled water: some air bubbles soon appeared on the charcoal: and +in about two hours reduced gold was evident on its lower surface, and +increased gradually, till the charcoal was nearly coated with gold of +its proper colour. + +This experiment was repeated with a richer solution of gold; the +reduction did not commence near so soon, nor was the quantity reduced +so great, or brilliant, as in the preceding experiment. + + +EXP. 2. GOLD. + +A small bit of charcoal was suspended in a solution of gold in +ether: an effervescence immediately commenced, and continued for a +considerable time: but the solution suffered no change of colour; nor +was there a particle of the gold reduced. + +I should not be surprised, if the gold were reduced in this experiment, +as charcoal contains a large quantity of water, which it powerfully +attracts from the surrounding air: however not a vestige of reduced +gold could be perceived. + +Bits of charcoal were suspended in the same manner in most of the +metallic solutions treated of in this essay: no change was perceived on +those immersed in solutions of arsenic, manganese, and fused nitrate of +silver in water: but a bit immersed in a solution of the same nitrate +in alcohol, had parts of it covered with bright sparkling particles, +which seemed to vegetate from the charcoal, and were evidently reduced +silver: for they were not soluble in water, on the surface of which the +bit of charcoal deposited some small spangles of great lustre. The bits +immersed in solutions of sulphate of iron and zinc exhibited some very +faint signs of reduction. + +But these experiments were not repeated, nor sufficiently varied, to +enable us to form a just opinion of the power of charcoal in reducing +metals in this way. + +A small quantity of charcoal, reduced to fine powder, was digested +several days in a strong solution of caustic potash in alcohol; the +phial was frequently shaken to promote the solution. + +Some of the clear solution, which was of a reddish colour, was poured +into a phial for use. + + +EXP. 3. GOLD. + +A few drops of this solution of charcoal, or carbone, were applied to a +bit of silk; after the alcohol evaporated, a solution of gold in ether +was dropped on, and immediately produced a brown, which, in about half +an hour, was changed to a purple hue, owing to water attracted from the +air; but no other sign of reduction appeared. + +Another bit of silk was immersed in the solution of carbone, and when +the alcohol evaporated, a few drops of an aqueous solution of gold +were applied; a brown stain was instantly formed; the silk was kept wet +with water; the stain gradually assumed a purple tinge, and, in about +five minutes, some reduced gold of its proper splendour, and colour, +appeared: and in some time after every part of the silk, to which the +solutions of carbone and gold were applied, was coated with reduced +gold, which remained permanent. During the experiment, it is necessary +to keep the silk constantly wet with water. + +If the solution of gold be applied before the alcohol evaporates, +a black precipitate is formed, along with the brown stain. In an +experiment made in this manner, a metallic film, whitish, and obscure, +appeared in the beginning; but soon vanished: and in some time after +the gold was reduced of its proper colour; and a speck of ruby red +appeared on the margin. + +The silk viewed by transmitted light presented various colours, as +purple, blue, and some green. + + +EXP. 4. SILVER. + +A few drops of the solution of carbone were applied to a bit of silk; +when the alcohol evaporated, a solution of fused nitrate of silver in +alcohol was applied: a light brown stain was immediately produced in +the silk; but no reduced silver could be seen. + +The solution of carbone was applied to another bit of silk, and when +the alcohol evaporated, an aqueous solution of fused nitrate of silver +was dropped on: a brown stain was instantly formed, and, in about ten +minutes, minute films of reduced silver were visible. + +The silk was kept wet with water during the experiment; and the brown +stain was gradually changed to black. In some little time the metallic +films disappeared. + +If the solution of silver be applied to the silk, before the alcohol +evaporates, black and brown precipitates are immediately formed; and +commonly no reduced silver can be seen; but sometimes very minute films +appear. + + +EXP. 5. PLATINA. + +To a bit of silk, which was immersed in a solution of nitro-muriate of +platina in distilled water, and dried in the air, a few drops of the +solution of carbone were applied; but no visible change was produced. + +Another bit of silk was dipped in the solution of carbone, and when +the alcohol evaporated, a few drops of the solution of platina were +applied: a yellow precipitate was immediately formed, and, in about ten +minutes delicate films of reduced platina were visible: these metallic +films soon vanished; and nothing but a yellow stain and the precipitate +remained. + +A bit of calico, on which this experiment was repeated, transferred a +bright film of reduced platina to the surface of water. + +During the experiments, the silk and calico were kept wet with water. + + +EXP. 6. MERCURY. + +On a bit of silk, which was immersed in a solution of oxygenated +muriate of mercury in distilled water, and dried in the air, a little +of the solution of carbone was dropped; but the silk underwent no +visible change. + +Another bit of silk was dipped in the solution of carbone, and, when +the alcohol evaporated, a little of the same solution of mercury was +applied; a yellow precipitate was immediately formed; and soon after +small films of reduced mercury appeared on the margin of the stain. + +This experiment was repeated with a solution of nitrate of mercury, and +the reduction of the metal was very evident on the margin of the stain, +which was black: the precipitate on the bit of silk was of the colour +of sulphur. + + +EXP. 7. COPPER. + +To a bit of calico, which was immersed in a solution of acetite of +copper in distilled water, and dried in the air, a few drops of the +solution of carbone were applied; but no visible change was produced. + +On another bit of calico, which was dipped in the same solution +of copper, some of the solution of carbone was dropped: the calico +acquired a slight tinge of brown; it was kept wet with water; and, in +about twenty minutes, several white metallic films were evident. + +A bit of silk, on which this experiment was made, acquired a beautiful +red colour, similar to the ruby red, with which copper tinges glass, +and depending on the same cause, viz. the quantity of oxygen combined +with the metal. + + +EXP. 8. LEAD. + +A bit of white calico was immersed in a solution of acetite of lead in +distilled water, and dried in the air: then a few drops of the solution +of carbone were applied; but no visible alteration took place. + +On another bit of the same calico, which was dipped in the solution +of carbone, a little of the same solution of lead was dropped; and +in a few seconds films of reduced lead, bright as silver, appeared: +the calico was then immerged in water, and transferred a continuous +pellicle of reduced lead to its surface. + +This experiment was often repeated both on silk, and calico: sometimes +the lead is reduced in an instant; but at other times five or six +seconds elapse, before any reduced lead becomes visible. + +I also found, that a solution of potash in alcohol reduces lead; +but not so soon, or effectually, or in such quantity, as the former +solution does; but it is evident, that these solutions differ only in +the quantity of carbone, which they contain. + + +EXP. 9. TIN. + +To a bit of calico, which was immersed in a solution of muriate of +tin in distilled water, and dried in the air, some of the solution of +carbone was applied: but no signs of reduction appeared, nor was the +colour of the calico much altered. + +On another bit of calico, which was dipped in the solution of carbone, +some of the same solution of tin was dropped: a white precipitate was +instantly formed, attended with bright films of reduced tin: the calico +was immerged in water; and left a bright metallic film on the surface +of that fluid. + +The same experiment succeeds on silk. + + +EXP. 10. BISMUTH. + +A piece of silk, which was immersed in a solution of nitrate of +Bismuth in distilled water, and dried in the air, suffered no visible +alteration, on applying the solution of carbone. + +To a bit of calico, which was dipped in the solution of carbone, a few +drops of the same solution of bismuth were applied; and immediately +films of reduced bismuth were evident. The calico was immerged in +water, and transferred a bright metallic film to its surface. + +This experiment succeeded also on silk. + + +EXP. 11. ARSENIC. + +A bit of silk was immersed in a solution of muriate of arsenic in +distilled water, and dried in the air, then a little of the solution of +carbone was dropped on the silk; but no visible alteration took place. + +Another bit of silk was dipped in the solution of carbone, and when the +alcohol evaporated, some drops of the same solution of arsenic were +applied; and in a short time a few minute metallic films were visible +on the silk, which, when transferred to water, were still more so. + +Tartarite of antimony, treated in the same manner, transferred a very +delicate film, scarcely visible, to the surface of water. + + +EXP. 12. IRON. + +A bit of calico, which was dipped in a largely diluted solution of +sulphate of iron, and dried in the air, suffered no perceptible change, +on applying the solution of carbone, except a slight tinge of brown. + +Another bit of calico was immersed in the same solution of iron, and +placed on a bit of deal board, a few drops of the solution of carbone +were then applied: the calico was kept constantly wet with water, and +in about fifteen minutes films of reduced iron were visible: the calico +was immersed in water, and left a bright metallic film on its surface. + + +EXP. 13. ZINC. + +To a bit of silk, which was dipped in a largely diluted solution of +muriate of zinc, and dried in the air, a few drops of the solution of +carbone were applied; but scarce any alteration of colour, or other +visible change, occurred. + +A piece of calico was immersed in the same solution of zinc, and placed +on a bit of thin deal board, a few drops of the solution of carbone +were then applied: the calico was kept constantly wet with water; and +in about fifteen minutes films of reduced zinc were evident: the calico +was immerged in water, and transferred a very bright metallic film of +the colour of zinc to its surface. + +I also reduced muriate of cobalt in this manner. + + +EXP. 14. MANGANESE. + +To a bit of silk, which was dipped in a diluted solution of nitrate of +manganese, and dried in the air, some drops of the solution of carbone +were applied; but nothing appeared, except a brown stain. + +Another bit of silk was immersed in the solution of carbone, when the +alcohol evaporated, a few drops of the same solution of manganese were +applied: a brown stain was soon produced; the silk was kept wet with +water, and in about twenty minutes films of reduced manganese of a +bluish white colour were evident on the silk. + +This experiment did not succeed with a strong solution of nitrate of +manganese. + +The same experiment succeeds also on linen, and calico, both with +nitrate, and sulphate of manganese; the reduction is attended with +violet, and purple, colours, such as this metal imparts to glass, +and other substances, in which it exists combined with different +proportions of oxygen: this difference is the cause of the different +colours, which solutions of manganese assume. + +The bright films of reduced manganese soon disappear, the cause of +which has been explained in the first chapter of this essay: the +explanation there offered is confirmed by the following facts. + +“Regulus of Manganese,” says Mr. Bergman, “when well fused generally +persists in a dry place, but sometimes undergoes spontaneous +calcination, and falls down in a brownish black powder. + +“Moisture, but particularly the access of aerial acid, assists this +operation. A small piece, put into a dry bottle, well corked, remained +perfect for the space of six months, but afterwards, exposed to the +open air of a chamber for two days, contracted a browness on its +surface, together with so much friability as to crumble between the +fingers. The internal parts, however, retained an obscure metallic +splendour, which disappeared in a few hours[18].” + +I shall now relate a few experiments made with ether, alcohol, and gum. + + +EXP. 15. GOLD. + +I evaporated a solution of gold in nitro-muriatic acid to dryness, +and dissolved the salt in pure alcohol: the solution was poured into +a phial carefully dried in hot sand, and rinced with pure alcohol: +the solution filled about ¾ of the phial, which was carefully corked, +and though it was nine months exposed to the gray light, no films of +reduced gold appeared. + +Part of the same solution was poured into a phial, and diluted with +water; films of reduced gold soon appeared. + + +EXP. 16. GOLD. + +A phial half filled with a solution of gold in sulphuric ether was +exposed nine months to the gray light; but no films of reduced gold +were produced. + +On a bit of silk, which was dipped in part of the same solution of +gold, and exposed to the gray light, and kept wet with water, reduced +gold appeared in the space of a few hours. + + +EXP. 17. GOLD. + +I mixed an aqueous solution of gold with a solution of gum arabic in +distilled water, in such proportion, as to prevent the solution from +spreading in the silk. + +With this solution I drew several stripes on a piece of silk, and +exposed it to the gray light of a chambre: in some time the gold was +reduced attended with blue, and purple, colours. + +Similar stripes were drawn on another piece of silk, which, after the +stripes became sufficiently dry, was placed over the vapour of hot +water; and in about fifteen minutes the gold was reduced in a beautiful +manner. + +This solution was applied to another bit of silk, which, after it +became sufficiently dry, was placed between the leaves of a blank book, +to exclude the action of light; the gold, after some time, was reduced. + +I found that small stripes, and spots, made with this solution, were +reduced by breathing on them for some time. + +Sugar also, mixed with the solution of gold, promotes the reduction; +but not so well as gum. + +A bit of silk was dipped in a solution of nitrate of silver in +distilled water, and exposed, while wet, to the smoke of a common fire; +in a short time reduced silver appeared. + +The following inferences are deducible from the experiments related in +this chapter. + +1. Charcoal is capable of reducing the metals in the ordinary +temperature of the atmosphere. + +2. Water is essential to the reduction of metals by charcoal: for these +experiments prove, that the reduction cannot be effected without water. + +3. Charcoal does not reduce the metals by giving them phlogiston; nor +by uniting with, and separating, their oxygen; for were either of these +opinions true, metallic solutions in ether, and alcohol, should be as +effectually reduced by charcoal, as metallic solutions in water are. + +4. Ether, and alcohol do not promote the reduction of metals without +the aid of water: but when this is present in sufficient quantity, they +effect the reduction, in the same manner, that charcoal, and other +combustible bodies do. + +It is evident then that charcoal reduces the metals by decomposing +water; which seems to be effected in the following manner. + +The carbone of the charcoal attracts the oxygen of the water, while the +hydrogen of the latter unites, in its nascent state, with the oxygen of +the metal, and reduces it. + +Hence it follows that the carbone is oxygenated by the oxygen of the +water, and forms carbonic acid, while the metal is restored to its +combustible state. + +This explanation is supported by the following fact: M. Gengembre +has observed, that if charcoal be immersed in water, and kept at a +temperature of 30 degrees of the thermometer of M. De Reaumur, the +water is gradually decomposed, and inflammable gas is formed[19]. + +That charcoal effects the reduction of metals, in high degrees of heat +also, by decomposing water, is evident from the following observations. + +The great force with which charcoal attracts water is a fact +sufficiently established; Dr. Priestley is so convinced of this, that +he expresses himself in the following strong terms. “I did not know, +nor could believe the powerful attraction, that charcoal, or iron, +appear to have for water; when they are intensely heated, they will +find, and attract it in the midst of the hottest fire through any pores +in the retort[20].” + +Now since water is essential to the reduction of metals in low degrees +of heat; and since that fluid is always present, when metals are +reduced by charcoal in high degrees of heat; it is manifest, that +charcoal acts in the same manner in both these temperatures; and since +water is easily, and instantly, decomposed by charcoal at a red heat, +as the Antiphlogistians themselves allow; it clearly follows that their +theory of metallic reduction is erroneous: for since the water is +instantly decomposed by the charcoal, it is a necessary consequence, +that its carbone must unite with the oxygen of the water, while the +hydrogen of the latter unites, in its nascent state, with the oxygen +of the metal, and reduces it, forming a new quantity of water equal to +that decomposed: this new quantity of water may be decomposed in its +turn: so that a thimble full of water would be sufficient to reduce any +quantity of metal; provided the water were prevented from escaping, and +time enough allowed. + +Beside this source of water, the air of the atmosphere, which +contributes to support the fire is an inexhaustible magazine of water: +and the hotter the air is, the more water it holds in solution; as +M. Le Roy has demonstrated[21]. Moreover all metallic oxids and ores +contain a large proportion of water. + +From this view it appears, that the manner, in which charcoal, and +other combustible bodies, effect the reduction of metals, is by +assisting to decompose water, the hydrogen of which is therefore the +only reducer of the metals. + +In order to point out the difference between this opinion, and that of +the Antiphlogistians, I shall present the reader with M. Lavoisier’s +idea of metallic reduction. + +“It can not be doubted,” says that celebrated chymist, “that charcoal +at a red heat takes oxygen from all metallic substances: this is a fact +against which no exception can be made: and it is the foundation of the +whole theory of metallic reduction.” + +But the experiments in this essay demonstrate, that this assertion +is erroneous in every instance of metallic reduction: for so far is +it from being true, that charcoal takes oxygen from all metallic +substances, that it never does so in one single instance; since its +carbone always unites with the oxygen of the water, the hydrogen of +which unites immediately to the oxygen of the metal, and reduces it. + +“But this action of charcoal on oxygen,” adds M. Lavoisier, “this +property, which it possesses of taking it from metallic subsubstances, +is not so strong in the cold, as at a red heat, since we are +unacquainted with any metallic revivification effected by charcoal +without heat[22].” + +It is evident that this mode of reasoning is no longer of any weight; +since charcoal does reduce metals in the ordinary temperature of the +atmosphere. + +The reason charcoal is more powerful in high degrees of heat, than +other reducers of the metals, is its great fixity in the fire, and +the immense force, with which it attracts, and imprisons water in its +pores: thus preventing its escape till it be decomposed by an affinity, +which is much more complex than has been hitherto imagined. + +Another reason of the superior power of charcoal in metallic reduction +is, that it forms a volatile elastic fluid with the oxygen of the +water, which flies off; and consequently does not react on the metal, +or disturb, or impede, by its presence, the action of the reducing +powers: advantages that phosphorus, or any other combustible substance, +which forms a fixed acid, that reacts on the metal, can never possess. + + + + +CHAPTER VIII. + +REDUCTION OF METALS + +BY + +_LIGHT_. + + +The next substance, I shall treat of, is Light, which seems well +adapted to illustrate the theory of metallic reduction; as in +experiments made with this substance, water can be more effectually +excluded, than in trials with any other reducer of the metals. + +Before any decisive experiments could be made on light, or indeed +any other reducer of the metals, it is obvious that we should first +ascertain the effects of water itself in the ordinary temperature of +the atmosphere: to determine this point, the two following experiments +were made. + + +EXP. 1. GOLD. + +A piece of silk was immersed in an aqueous solution of nitro-muriate +of gold, and suspended in a phial over water: the phial was corked, +covered with black silk, and placed in a dark closet, to prevent the +action of light. The experiment was continued from the 20th of July +to the 20th of October, during which time the silk was frequently +observed, and found to continue moist: but no alteration could be +perceived, except that the yellow colour, which the solution of gold +gave the silk, was changed to a light brown. + +The silk was now taken out of the phial, and a solution of phosphorus +in ether applied to it: shortly after, a white metallic film appeared: +the silk was then kept wet with water, and in some time, reduced gold +of its proper colour appeared. + + +EXP. 2. SILVER. + +A bit of silk, which was dipped in an aqueous solution of nitrate of +silver, was suspended in a phial over water, and placed in a dark +closet, from the 20th of July to the 20th of October, and examined from +time to time; but no alteration could be observed; its white colour +continued pure, and unchanged. + +The silk was now taken out of the phial, and the silver was immediately +reduced by means of a solution of phosphorus in ether. + +Hence it appears, that water alone has not the power of reducing metals +in the ordinary temperature of the atmosphere. + + +EXP. 3. GOLD. + +On the 24th of July a piece of silk was immersed in a solution of +nitro-muriate of gold in water, and dried by a gentle heat; it was +then suspended in a window, exposed to the sunbeams, as much as +possible: no change was perceived on it, till the 26th, when the margin +of the silk began to assume a purple tinge, which increased gradually, +and on the 29th exhibited a few obscure specks of reduced gold on the +side of the silk opposed to the light. + +The purple tinge continued to increase, and the yellow, which the +solution of gold gave the silk, decreased gradually, till on the 27th +of August the colour was a mixture of purple, and light brown. + +The reduction of the gold seemed to keep pace with these changes of +colour, and was very evident on some parts of the silk even in the gray +light; but much more so in sunshine: these changes were observed till +the 20th of October; the experiment was then discontinued; and scarce +any reduced gold could be seen on the side of the silk not opposed to +the light. + +That this slight reduction of the gold, and changes of colour in the +silk, depended on water absorbed from the air of the chambre, will +appear from the following experiments. + + +EXP. 4. GOLD. + +A bit of silk, which was dipped in the solution of gold employed in +the preceding experiment, was dried, and suspended in a crystal phial +over dry carbonate of potash: the phial was then corked, and further +secured from external humidity by covering the cork with wax: it was +now placed in a dark closet 24 hours, that the carbonate of potash +might have sufficient time to attract all the moisture, it could, from +the air of the phial, before exposing it to the action of light. + +The phial was then placed in a window, exposed, as much as possible, +to the solar light, from the 24th of July to the 20th of October, and +carefully observed: the same side of the silk was always opposed to +the light, and had the yellow tinge, which the solution of gold gave, +altered to a brownish yellow: but the other side of the silk suffered +no visible change whatever; nor could any purple tint, or the smallest +vestige of reduced gold be perceived. + +Another bit of silk, which was immersed in the same solution of gold, +and dried by a gentle heat, was suspended over some dry carbonate of +potash, contained in a crystal phial covered with black silk, and +placed in a dark closet, during the same space of time, underwent no +visible change whatever. + +Both these bits of silk were now taken out of the phials, and the gold +was instantly restored to its metallic splendour by means of water and +a solution of phosphorus in ether: a proof that the nitro-muriate of +gold, in these bits of silk, suffered no change, during that space of +time. + + +EXP. 5. GOLD. + +A piece of silk, which was dipped in the same solution of gold, and +placed on a china plate exposed to the sunbeams, was kept moderately +wet with water during the experiment: the first alteration observed +was, that the yellow colour of the silk began to change to a faint +green, succeeded by a purple tinge, which in about fifteen minutes +exhibited some particles of reduced gold: soon after the threads of the +silk, which acquired this purple tint, were gilded with gold; and, in +about an hour, the whole of the silk was covered with a superb coat of +reduced gold, exhibiting the texture of the silk in a beautiful manner. + +The purple tinge, which attended the reduction verged in some parts on +red, and in others on blue. + +This experiment, which is very amusing, I have repeated times +unnumbered: and when the sun is powerful, and the solution of gold +properly prepared, and of due strength, the coat of reduced gold is so +bright, and dazzling, as to distress the eye of the beholder. + +I find, that the best way of preparing a solution of gold for +this purpose is to separate the oxid of gold from its solution in +nitro-muriatic acid by means of good ether. + +The silk may be dipped in this solution, and when the ether +evaporates, kept moderately wet with distilled water. + +It was with this solution in ether that I first reduced gold in the +fibres of silk, and it was by means of the same, I discovered, that +water was a necessary condition in these reductions by light. + + +EXP. 6. GOLD. + +A bit of silk, which was dipped in a solution of nitro-muriate of gold +in alcohol, and placed on a china saucer, exposed to the sunbeams, was +kept wet with alcohol for the space of an hour; but no change even +in the colour, which the solution of gold gave the silk, could be +perceived. + +The alcohol diffused the solution of gold unequally through the silk: +the rays of the sun being intercepted, suspended the experiment: +there was no sunshine on the following day: on the third day the silk +was again exposed to the sunbeams, and kept wet with alcohol, which +extracted a yellow tincture; a proof that the gold in the silk suffered +no degree of reduction: the sun shone pretty strong for an hour, or +more; and, at length, a faint tinge of purple, followed by some reduced +gold, appeared. + +The preceding experiments leave us no room to doubt, that the purple +tinge and the small quantity of reduced gold, that appeared in this +experiment, depended on water attracted from the air, or deposited in +the silk by the alcohol during its evaporation. + +Mr. Scheele reduced a solution of nitro-muriate of gold in water by +exposing it in a phial for a fortnight to the rays of the sun[23]. + +Mr. Lewis also made many experiments on the staining of marble, and +other substances with metallic solutions, and light[24]. + + +EXP. 7. SILVER. + +A piece of silk, which was immersed in a solution of nitrate of silver +in water, was dried by a gentle heat, and exposed to the light of the +sun as much as possible in the window of a chambre from the 20th of +July to the 20th of October. + +In less than an hour the silk acquired a reddish brown colour: next day +the colour became more intense, and gradually increased, till, on the +third day, it bordered on black, which increased slowly: at length part +of it became gray, and a few minute particles of reduced silver could +be distinguished: the black tinge gradually disappeared, and the silk +was of a reddish brown colour: the reduced silver had a gray cast. + +The following experiments demonstrate, that the changes of colour, and +the few particles of semireduced silver depended on water attracted +from the atmosphere. + + +EXP. 8. SILVER. + +A bit of silk was immersed in part of the same solution of nitrate of +silver in water, and dried in the dark: the silk retained its white +colour: it was then suspended over dry carbonate of potash in a crystal +phial, which was corked, and secured from the ingress of moisture by +covering the cork with wax. + +The phial was left in a dark closet 24 hours, that the salt might +imbibe as much moisture as possible from the silk, and air. + +The phial was then placed in a window, exposed, as much as possible, to +the rays of the sun, from the 24th of July to the 20th of October: the +silk scarcely suffered any visible change, except a very faint tinge of +reddish brown; which was best seen by transmitted light; for the silk +viewed by reflected light appeared nearly white: but that even this +tinge, slight as it was, depended on a minute quantity of moisture, +which the carbonate of potash was unable to extract, appears from the +next experiment. + + +EXP. 9. SILVER. + +A piece of silk was dipped in a solution of fused nitrate of silver in +alcohol, and carefully dried: it was then suspended over a quantity of +concentrated sulphuric acid in a crystal phial, which was coated with +a double fold of black paper, and gum arabic, reaching somewhat above +the level of the acid, to prevent the light from acting on it: the +phial was corked, and to exclude moisture more effectually, the cork +was covered with wax. + +The phial was now placed in a dark closet 24 hours, that the humidity +of the enclosed silk and air might be attracted by the acid: it was +then placed in a window, exposed as much as possible to the rays of +the sun, from the 19th of July to the 26th of October: but the silk +underwent no visible change whatever: its white colour remained pure, +and unaltered. + +The silk, at the end of this period, was taken out of the phial, and +wetted with water: a solution of phosphorus in ether was then applied +to it; and instantly the metallic splendour of the silver appeared. + +Another bit of silk, which was immersed in a solution of nitrate +of silver in water, and dried in the dark, was suspended over dry +carbonate of potash in a phial, and placed in a dark closet about two +months; the silk underwent no visible alteration whatever; its white +colour remained pure. + +I was desirous of knowing, if the nitrate of silver in this bit of silk +suffered any change, that might render it incapable of reduction: I +therefore took it out of the phial, and divided it into two parts: one +of these was wetted with water, and the silver was instantly reduced by +a solution of phosphorus in ether. The other part, which was suspended +in a window, exposed to the air of the chamber, and rays of the sun, +soon acquired a reddish brown colour. + +Hence it is evident, that these changes of colour indicate partial +reductions of the metal; and that they never happen without the +presence of water. + + +EXP. 10. SILVER. + +A bit of silk, which was dipped in a solution of nitrate of silver in +water, was placed on a China saucer, exposed to the rays of the sun, +and kept moderately wet with water: in a few minutes the white colour +of the silk was changed to a reddish brown, which by degrees became +darker; and, in about three or four hours, though the solar rays were +often languid, and intercepted, acquired a blackish gray colour, +most of the reddish brown having disappeared: next day there was no +sunshine; but towards the evening particles of reduced silver were +visible on the side of the silk opposed to the light. + + +EXP. 11. SILVER. + +A bit of silk, which was immersed in a solution of nitrate of silver +in alcohol, and exposed to the beams of the sun, as in the preceding +experiment, was kept moderately wet with alcohol; but resisted the +action of the light much longer than the preceding: however, in some +time, specks, and lines, of a reddish brown, began to appear on some +parts of the silk: next day, though there was no sunshine, the reddish +brown colour increased a little: on the third day, it became more +intense; but no black, or gray colour, or particle of reduced silver, +could be observed. + +Whoever compares this with the preceding experiments, can have no +doubt that the changes of colour, which appeared in this experiment, +depended on water attracted from the air, or deposited in the silk by +the alcohol during its evaporation. + +The experiments detailed in this Chapter, prove beyond the power of +contradiction, + +1. That water is essential to the reduction of metals by light: for +these experiments demonstrate, that the reduction can not take place +without water, and that it is always in proportion to the quantity of +that fluid present. + +2. That light does not reduce metals by giving them phlogiston, as +Messrs. Macquer and Scheele supposed; for were this opinion true, light +should reduce them without the aid of water, and as well with alcohol +as with water. + +3. Light does not reduce metals by fusing and expelling their oxygen, +as the antiphlogistians imagine; for were this its mode of agency, the +reduction should happen without the assistance of water, and as well +with alcohol as with water. + +4. Light is a combustible body; for it acts like hydrogen, phosphorus, +sulphur, and charcoal, in the reduction of metals. + +Since water then is essential to the reduction of metals by light, +and since light does not reduce metals by giving them phlogiston, +nor by fusing, and expelling their oxygen, it follows, that the +water is either decomposed, or that it unites with metallic earths, +and constitutes their phlogiston, or that it unites with, and +separates their oxygenous principle: but as the two last suppositions +are inadmissible, it is obvious that light reduces the metals by +decomposing water. + +After explaining the manner in which other combustible bodies reduce +the metals by decomposing water; it will not be difficult to explain +how light too produces the same effect. + +But in order to facilitate the explanation, it must be premised, + +1. That it is a law of attraction, that, when any body is deprived, to +a certain degree, of another, for which it has a strong affinity, the +attraction of the former for the latter is much increased. + +2. That light has a strong attraction for oxygen, or the base of vital +air. + +3. That when oxygen is condensed, and fixed in any substance, it +contains much less light, and caloric, than it does in the gazeous +state. + +4. That the oxygenous principle exists in water in this condensed +state, and consequently has a strong attraction for light. + +Therefore, when light reduces the metals, it attracts the oxygen of the +water, while the hydrogen of the latter unites, in its nascent state, +to the oxygen of the metal, and reduces it, forming at the same time a +quantity of water equal to that decomposed. + +Hence it follows that the light is oxygenated, and changed into vital +air, while the metal is restored to its combustible state. + + + + +CHAPTER IX. + +REDUCTION OF METALS + +BY + +_ACIDS_. + + +It is well known that solutions of gold throw up films of the reduced +metal to the surface of the fluid, and sides of the phials that contain +them. + +It has been shown, chap. 7th, that this effect depends on the presence +of water, which is further illustrated by the following experiments. + + +EXP. 1. SILVER. + +A dram of saturated solution of nitrate of silver in distilled +water was mixed with half an ounce of vinegar, in a few minutes, a +precipitate was formed: the whole was then poured on a filter, and +washed with distilled water: the precipitate acquired a bluish gray +metallic appearance: the liquor, which passed the filter, got a brown +colour, and became blackish: next day bright films of reduced silver +floated on the liquor; and in some months after, a considerable part +of the inner surface of the phial was coated with reduced silver. +Distilled vinegar did not produce this effect. + + +EXP. 2. PLATINA. + +If a solution of the ore of platina in nitro-muriatic acid be +evaporated to dryness; and the salt dissolved in water, films of a +livid white metallic appearance are thrown up to the surface. + + +EXP. 3. TIN. + +Some tin, which was dissolved in a china cup in muriatic acid, and +evaporated to dryness, was dissolved in distilled water; immediately +white metallic films appeared on the surface of the liquor; and after +some hours, the whole surface of the solution was covered with a +continuous metallic pellicle, which reflected all the colours of the +rainbow, in a beautiful manner. + + +EXP. 4. MERCURY. + +Mr. Bergman says, “calcined mercury is reduced by digestion in acid of +salt; but the cause has not yet been sufficiently explored[25].” + +As this reduction of mercury by muriatic acid is doubted of by some; I +made the following experiment. + +A quantity of precipitate _per se_ was put into a china cup, placed +on hot sand, and some muriatic acid was poured on it: the oxid was +gradually dissolved, and the digestion continued, till the acid was +nearly evaporated: some distilled water was then poured on the salt, +and minute films of a bright metallic appearance floated on the surface. + +A nitrate of mercury was evaporated to dryness; the salt acquired a +slight tinge of yellow; the cup was removed from the hot sand, and +some water poured on the salt: immediately bright films of reduced +mercury appeared; and in about three or four hours the whole surface +of the solution was covered with a metallic pellicle, parts of which +had the colour and splendour of the metal; and other parts reflected a +wonderful variety of the most beautiful colours. + + +EXP. 5. ARSENIC. + +A quantity of white oxid of arsenic and muriatic acid was digested in +the same manner in a china cup; a smart heat was continued, till most +of the acid evaporated, and left behind a mass of the consistence of +tar: the surface of which had a gray appearance; after it cooled, some +distilled water was poured on, it diffused a disagreeable smell, and +films of reduced arsenic were thrown up to the surface; these were for +some time remarkably bright, but soon became of a dull gray colour, +owing to the rapid tendency of this metal to spontaneous calcination. + + +EXP. 6. MANGANESE. + +Some concentrated sulphuric acid was poured on a quantity of the black +oxid of manganese in a china cup, placed on hot sand: an effervescence +was visible, but no sulphurous acid gas was exhaled: the cup was +removed from the sand, before any perceptible quantity of the acid +evaporated: then some water was poured on the mixture: and instantly +the surface of the fluid was covered with very brilliant metallic +films: and, at the same time, the solution acquired a rose colour. + +Some of the same oxid of manganese was dissolved in nitric acid, in +which a bit of sugar was put: the solution was poured into a china cup, +placed on hot sand, and, as the evaporation proceeded, bright metallic +films appeared on the surface. + +Mr. Bindheim of Moscow relates, that he reduced the aërated calx of +manganese dissolved in nitrous acid: “the solution was placed upon an +open fire in a glass retort[26].” + +Happening to pour out a very largely diluted solution of sulphate of +iron, I was surprised to find the flags of the court in an hour or two +after, covered with large films of a livid white metallic aspect: +these films, after the water evaporated, remained on the flags several +days. + +In consequence of this I poured a largely diluted solution of sulphate +of iron into several shallow vessels, and always found the surface of +the solution covered with abundance of bright metallic films. + +I also found that a largely diluted solution of muriate of zinc throws +up bright metallic films to the surface. + +The reduction of metals by acids is a very convincing proof of the +decomposition of water, and seems inexplicable on any other principle. + +The reduction and calcination of metals by heat and electricity are +naturally explained on the same principle: Doctor Priestley informs us +in his History of Electricity, Vol. I. p. 344, that S. Beccaria revived +several of the metals by the electric shock. It is obvious that the +electric fluid produces this effect in the same manner, that other +combustible bodies do, viz. by decomposing water. When the red oxid +of mercury is reduced in close vessels by heat; the latter attracts +the oxygen of the water, contained both in the oxid, and in the air of +the vessels, while the hydrogen of the water unites to the oxygen of +the mercury, reduces it, and forms a quantity of water equal to that +decomposed. + +It is found, that if light and caloric act both at the same time, +the reduction is effected with more facility, than if either acted +separately: in this case, the superior efficacy of the combined action +of light, and caloric resembles that of other compound reducers of the +metals; as that of sulphurated hydrogen gas, phosphorated hydrogen gas, +alkaline sulphure, &c. which are more powerful than simple hydrogen +gas, sulphur, or phosphorus. + +This superior efficacy of compound reducers, is similar to what happens +with some other combinations of combustible bodies, as pyrites, +pyrophori, a mixture of lead and tin, &c. which have a more powerful +attraction for oxygen, than any of their ingredients, in a separate +state. + +Other acids, as the gallic, the tartarous, the formic, &c. and also +alkalis, as ammonia, and soda, have the power of reducing some of the +metals, facts well known to chymists. + + + + +CHAPTER X. + +OXYGENATION + +OF + +_COMBUSTIBLE BODIES_. + + +It has been shown, in the preceding chapters, that water is essential +to the reduction of metals; that it is always decomposed in that +process; and that the reducing substances are oxygenated by the oxygen +of the water, while the hydrogen of the latter reduces the metals. + +That water is also decomposed in every instance of oxygenation, and +that the oxygen of water alone oxygenates combustible bodies, will +appear from the following observations. + + +AZOTE. + +The first case of oxygenation, we shall consider, is that of _azote_, +in an experiment of Dr. Priestley, which has been urged by Mr. Kirwan +with great success against the Antiphlogistians. + +“If the electric spark be taken in nitrous air, it will be reduced to +⅓ of its bulk, and the residuum is mere phlogisticated air, and a +little acid is deposited. Now the Antiphlogistians own that nitrous +air contains both pure air and phlogisticated air; since, therefore, +this pure air disappears, is it not evident that it was converted +into water? and since the formation of water requires the presence of +inflammable air, does it not follow that the nitrous air contained this +also[27]?” + +To this objection M. Berthollet replies, that the diminution of the +nitrous gas “is owing to the combination of the mercury with the +oxygene, which existed in the gas[28].” + +But this answer is insufficient; as it does not account for the +water, and acid, that appeared: and indeed, by this experiment, +the Antiphlogistians are refuted on their own principles, and the +decomposition of water is incontestably proved; for as nitrous acid +could not be formed without more oxygen than what existed in the +nitrous air, is it not evident, that this oxygen must be derived from +the water contained in the nitrous air? It is obvious then, that the +water of the gas was decomposed; which seems to have been effected in +the following manner. + +The electric spark diminishes the attraction of the constituent +principles of the water for each other; hence the azote of the gas +unites with the oxygen of the water, while the hydrogen of the latter +combines with the oxygen of the gas; and thus water and nitrous acid +are formed. + +The formation of nitrous acid in Mr. Cavendish’s noted experiment, +cannot be explained on any other principle than the decomposition of +water: when the electric spark is taken in a mixture of azotic gas, +and vital air; the water of these airs is decomposed: the electric +flame lessens the force, with which the oxygen and hydrogen of the +water adhere; hence the azote seizes the oxygen of the water, and forms +nitrous acid, while the hydrogen of the water unites with the oxygen of +the vital air, and forms a quantity of water equal to that decomposed. + +When nitrous, and vital air, are mixed; the whole mass “hisses, turns +red, grows warm, and contracts in bulk,” the azote of the nitrous air +attracts the oxygen of the water, and forms nitrous acid, while the +hydrogen of the water unites in its nascent state with the oxygen of +the vital air, and forms a quantity of water equal to that decomposed. + +Hence while the azote of the nitrous air is oxygenated; the caloric is +restored to its combustible state. + +“But it is to be observed,” says M. Bergman, treating of this +experiment, “that the decomposition of nitrous air is the effect of a +double attraction; the phlogiston is attracted by the vital air, and +the acid part by the water. Therefore, when the mixture is made in a +phial immersed in mercury, the experiment fails[29].” + + +HYDROGEN. + +The combustion of hydrogen gas with vital air is explicable only on the +decomposition of the water contained in these airs: thus when flame, +or a glowing body is applied to a mixture of them; the attraction of +the principles of the water for each other is diminished; therefore +the hydrogen of the inflammable air unites with the oxygen of the +water, while the hydrogen of the latter seizes the oxygen of the +vital air: thus the whole bulk of the airs, which are changed into +water, disappears; and their light, and caloric, are restored to the +combustible state. + +Hence it appears that water is not formed during the combustion of +vital, and inflammable air, in the manner the Antiphlogistians suppose. + +Indeed it is obvious, that, if these airs contained no water, they +could never be burned: for since they are already saturated with light, +and caloric, they can have no attraction for any additional quantity +of these fluids; and consequently can suffer no other change from +the light, or caloric, of a glowing body, than a greater degree of +expansion, and therefore could never unite. + +The same reasoning applies to the combustion of all elastic fluids. + + +PHOSPHORUS. + +Vital air always contains a large proportion of water: when phosphorus +is burned in this air, it attracts the oxygen of the water, and forms +phosphoric acid, while the hydrogen of the water unites with the oxygen +of the gas, and forms water, which unites with the acid. + +Hence the weight of the acid formed is equal to the weights of the +oxygen gas, and phosphorus, consumed; and the light and caloric, which +appear during the combustion, are restored to their combustible state. + +This explanation is confirmed by an observation of Mr. Bergman, who +says, + +“In vital air, without the aid of external heat, phosphorus is consumed +very slowly, and scarce at all, unless water be present[30].” + +Therefore the phosphorus does not unite to the oxygen of the vital air, +as M. Lavoisier supposes, but to the oxygen of the water contained in +the oxygen gas. + + +SULPHUR. + +When sulphur is burned in vital air, it attracts the oxygen of the +water, and forms sulphuric acid, while the hydrogen of the water +attracts the oxygen of the gas, and forms a quantity of water equal to +that decomposed: the light and caloric are at the same time restored to +their combustible state. + +The sulphur then does not unite with the oxygen of the vital air, +as the Antiphlogistians imagine, but with the oxygen of the water +contained in that gas. + + +CHARCOAL. + +In like manner during the combustion of charcoal in vital air, the +carbone attracts the oxygen of the water, and forms carbonic acid, +while the hydrogen of the water unites with the oxygen of the vital +air, and forms a new quantity of water equal to that decomposed. + +Hence the carbone of the charcoal does not unite with the oxygen of the +vital air, as M. Lavoisier supposes, but with the oxygen of the water +contained in that gas. + +That water is decomposed in every instance of combustion, is further +proved by attending to what passes during the burning of a common fire: +the carbone of the fuel combines with the oxygen of the water, and +forms carbonic acid, while the hydrogen of the water unites partly +with the oxygen, and partly with the azote of the atmosphere, and forms +water, and the ammonia, which abounds in soot. + +From these observations it is evident, that M. Lavoisier’s account of +the formation of water, and acids, is erroneous, and inadequate to +explain the phenomena. + +The different kinds of fermentation are so many instances of the +decomposition of water: in every case of them, combustible bodies are +oxygenated by the oxygen of the water, while others are restored by its +hydrogen to their combustible state. + +Hence the azote, ammonia, and carbonic acid of fermentation, the +inflammable air of marshes, mines, &c. the azotic, and hydrogen +gas, ascending into the atmosphere, and there meeting the vital air +discharged from the water of plants, &c. form new quantities of air, +and water. + +When the azote is oxygenated, it unites with the oxygen of the water +contained in the air, and forms atmospheric air, and sometimes perhaps +nitrous acid, the hydrogen of the water combines, at the same time, +with the oxygen of the vital air, and forms a quantity of water equal +to that decomposed. + +But when the hydrogen is oxygenated, a quantity of water double that +decomposed is regenerated; for the hydrogen of the gas unites with the +oxygen of the water, while the hydrogen of the latter seizes the oxygen +of the vital air: and thus a quantity of water double that decomposed +is formed, and that part of it which the atmosphere cannot suspend +descends in the form of rain. + +When these decompositions are rapid, the phenomena of thunder and +lightning appear. + +This account of the renovation of our atmosphere explains why the +phenomena of thunder and lightning appear sometimes with, and sometimes +without rain, and also accounts for the production of the nitrous acid, +which Mr. Margraaf discovered in the purest snow. + +The breathing of fishes is a striking proof of the decomposition of +water in respiration. + +For this view of the formation of our atmosphere I am indebted to a +friend well acquainted with the experiments related in this essay, and +also for the application of the opinion which I venture to advance, to +the respiration of animals. + +The phenomena of vegetation cannot be explained on any other principle, +than the decomposition of water by heat, and light, which uniting to +the oxygen of the water contained in vegetables change it into streams +of vital air, that serve to renovate our atmosphere: the hydrogen of +the water, at the same time, contributes to form the oil and other +principles of plants, and when these are decomposed by the various +processes of combustion, forms a quantity of water equal to that +consumed in their formation. + +The changes, which nitric acid suffers by exposure to heat, or light, +are explained with ease on this principle: the light unites with the +oxygen of the water contained in the nitric acid, and forms vital air, +while the hydrogen of the water combines with the oxygen of the acid, +and forms a new quantity of water equal to that decomposed: thus the +nitric is converted into the ruddy nitrous acid. + + +METALS. + +According to the Antiphlogistians, “In every metallic solution by an +acid, the metal, in order to become oxided, decomposes either the acid +itself, or the water of solution, or it obtains from the atmosphere the +requisite quantity of oxygene. In the second case, hydrogenous gas, in +a state of greater or less purity is disengaged; and the acid remains +entire without decomposition, which is proved by the quantity of alkali +necessary to saturate it. In the first case, one of the principles of +the acid, or the acid deprived of part of its oxygene, is disengaged, +and fused in the caloric, which is separated at the same time; such are +nitrous gas, and sulphurous acid gas. In the third case, neither the +water nor the acid are changed; such is the solution of copper by the +acetous acid. + +“The muriatic acid, and the vegetable acids, which are formed of +radicals, or acidifiable principles, which have more affinity with +oxygene, than the metals have, are not decomposed by these metals, +and the oxygene is always afforded to these last by the water or +atmosphere. Hence the solutions by these acids afford only hydrogenous +gas, or do not effervese at all. + +“There are some cases in which the water and the acid are at the same +time decomposed by the metal, as in the solution of tin in the nitric +acid, according to the observation of M. De Morveau.” + +“Tin is so greedy of oxygene, and requires so large a quantity for its +saturation, that after having absorbed that of the nitric acid, and +reduced it to the state of azote, it decomposes likewise the water, +and disengages hydrogene. These two principles being separated from +their first compounds, unite together, and immediately form ammoniac. +Hence there is no disengagement of elastic fluid. In this case it +appears, that the formation of ammoniac, in the solution of tin by the +nitric acid, always takes place; for by throwing quicklime, or caustic +fixed alkali, into this solution, there is always a disengagement of +ammoniac[31].” + +It is evident, then, that this account of the oxygenation of metals, +given by the Antiphlogistians, is equally complex, as their account +of metallic reduction, and improbable; since every case, in which +they deny the decomposition of water, and derive the oxygen from other +sources, is easily, and naturally explained on that principle, as will +appear from what follows. + +Thus when mercury, or silver, is dissolved in nitric acid; the metal +attracts the oxygen of the water, while the hydrogen of the latter +unites with, and separates, more or less of the oxygen of the acid, +which is thus changed into nitrous air. + +The same thing happens during the solution of other metals in this +acid; the only difference being the greater or less energy, and +rapidity, with which they combine with the oxygen of the water. + +This decomposition of water is confirmed by the solution of tin in this +acid; in which the Antiphlogistians allow the decomposition of the +acid, and the water too; for ammonia is formed by part of the hydrogen +of the water, and azote of the acid. + +In every case of metallic solution by sulphuric, and muriatic acids, +whether concentrated, or diluted, water is decomposed: the metals +attracting the oxygen of the water, while its hydrogen escapes in +the form of inflammable air, or unites partly with the oxygen of the +acid, and partly with caloric: hence the volatile sulphurous acid, and +muriatic acid air, obtained, always contain some hydrogen gas, as +appears from the following observation of M. Bergman. + +“By means of vitriolic acid, inflammable air is obtained from zinc, +and iron, as also by means of marine acid; but, from the other metals +dissolved in vitriolic acid, we obtain another species of air, called +_vitriolic acid air_; and, by the marine acid, another similar to +the former, called _muriatic air_, but both more or less mixed with +_inflammable air_[32].” + +Again, when copper is dissolved in the acetous acid; the copper +attracts the oxygen of the water, while the hydrogen of the latter +unites with the oxygen of the atmosphere, and forms water: hence no +effervescence appears. + +When alkalies dissolve metals, the latter are always oxygenated at the +expence of the water, which holds the alkali in solution: thus when +lead, and copper, are dissolved; the metals combine with the oxygen of +the water, while its hydrogen unites to the oxygen of the atmosphere, +and forms water: hence no hydrogen gas appears. + +The oxygenation of metals, and other substances by heat, and air, is +easily explained on the same principle: the metals, &c. unite with the +oxygen of the water contained in atmospheric air, while the hydrogen +of the water combines with the oxygen of the air, and forms a quantity +of water equal to that decomposed. + +This explanation is clearly proved by an experiment of Mr. Bergman on +the regulus of manganese, which, if kept in a dry place, retains its +metallic splendour; but, if exposed to moisture, is soon oxygenated, +and loses its lustre[33]. + +It is further confirmed by the authority of the distinguished Mr. +Scheele, who says, that “the water contained in common atmospheric air +is the chief cause of the ignition of pyrophorus,” which he proved by +the following experiment. + +“I made a very dry air by putting some very small pieces of quicklime +into a small matrass: then I put the neck of another matrass into +that of the first, so that the air of both might communicate; and I +luted the crevices with wax. Two days afterwards I separated the empty +matrass, and poured half an ounce of pyrophorus from my phial into +it, and immediately carefully shut the aperture up: but I did not +observe, that it grew in the least warm: an hour after this, I put a +sponge moistened in water into the matrass, and shut it up again: a few +minutes after the pyrophorus began strongly to be heated, and some +pieces kindled spontaneously[34].” + +Many other facts might be adduced to prove, that oxygenation cannot +take place without water, as the combustion of mixtures of iron +filings, sulphur and water, of alkaline sulphure and water, &c. in +which the water is decomposed, and the combustible bodies oxygenated by +its oxygen. + +It is evident then from the experiments and observations related in +this essay, that water is essential to the oxygenation of combustible +bodies; and that it is the only source of the oxygen that oxygenates +them: it is also evident, that when one body is oxygenated, another, +at least, is restored to the combustible state: hence it appears that +the oxygenation of combustible bodies is never effected by a single +affinity. + +The Antiphlogistians treating of the precipitation of metals by each +other, say, + +“Since the metals cannot remain united to the acids, but in the state +of oxides of a determinate degree, it is easily conceived, that by +plunging into a metallic solution a metal which has a stronger affinity +with oxygene than that which is dissolved, the former must deprive +the latter of its oxygene, take its place in the acid, and cause the +second to subside in a form more or less metallic, accordingly as it +has deprived it of more or less oxygene. This is the reason of the +precipitation of silver by copper, copper by iron[35],” &c. + +But this account of the precipitation of metals by one another cannot +be admitted; for it has been proved in every instance of reduction +related in this essay, that water is decomposed, and that its hydrogen +is the only substance that restores bodies to their combustible state. + +There is no reason then to suppose that nature deviates, in this +particular case, from that uniform simplicity, which she constantly +observes in all her operations. + +Therefore it is obvious, that, when one metal precipitates another in +a form more or less metallic; the precipitant unites with the oxygen +of the water, while the hydrogen of the latter combines with, and +separates, the oxygen of the precipitated metal, and thus reduces it. + +The experiments made with phosphorus and metallic solutions in ether, +alcohol, and water, prove the truth of this explanation; and show that +when one metal precipitates another in the metallic form, it acts like +a stick of phosphorus, decomposing the water. + +This account of the reduction of one metal by another is supported by +the opinion of Mr. Bergman, who says, + +“It is well known, that the calx of copper, dissolved in vitriolic +acid, is precipitated in its metallic form on the addition of iron; and +that by means of a double elective attraction; for the iron dissolving +in the acid would form an inflammable air by its phlogiston, were not +the copper present, which takes it up[36].” + +The same author remarks, that a small excess of acid is necessary, and +that without it no precipitation begins. + +Now since water is decomposed by iron and sulphuric acid, it must be +allowed, that, when iron is immersed in a solution of sulphate of +copper, the water is decomposed by the iron and excess of acid, the +iron attracting the oxygen of the water, while the hydrogen of the +latter, unites to the oxygen of the copper, reduces it, and forms a +quantity of water equal to that decomposed. + +The precipitation of silver in its metallic form by iron and other +metals is to be explained in the same manner: and not by a single +affinity, as the Antiphlogistians imagine. + +The reduction of gold, and some other metals, by solutions of sulphate +of iron, and muriate of tin, is readily accounted for on the principles +advanced here; for fresh made solutions of sulphate of iron, and +muriate of tin, contain hydrogen, and have the power of decomposing +water: the oxygen of which unites with the iron, and tin, while its +hydrogen seizes the oxygen of the gold, &c. reduces it, and forms a +quantity of water equal to that decomposed. + +The decomposition of water is further proved by the large dilution +necessary to form the arbor Dianæ, the purple precipitate of Cassius, +and other instances of the reduction of metals by one another. + + + + +CHAPTER XI. + +_CONCLUSION._ + + +I shall conclude with a general view of the inferences, which I +ventured to advance in this essay. + +1. Neither the Phlogistians, nor Antiphlogistians, account in a +satisfactory manner for the increase of weight, which bodies acquire +during combustion. + +2. Their account of the formation of water, acids, and oxids, is +erroneous; for it has been shown that the oxygen of water alone +oxygenates combustible bodies. + +3. Combustible bodies, as hydrogen, phosphorus, sulphur, charcoal, +light, &c. are capable of reducing the metals in the ordinary +temperature of the atmosphere; and indeed I might add, at a much lower +temperature, as I frequently experienced. + +4. Combustible bodies do not reduce the metals by giving them +phlogiston, as the Phlogistians suppose; nor by uniting with, and +separating their oxygen, as the Antiphlogistians maintain. + +5. Water is essential both to the reduction and oxygenation of bodies, +and is always decomposed in these operations. + +6. Water does not contribute to metallic reduction merely by +dissolving and minutely dividing the particles of metallic salts, and +thus removing the impediment opposed to chymical attraction by the +attraction of cohesion: for were this the case, metallic solutions in +ether and alcohol, in which that impediment is equally removed, should +be as readily and effectually reduced, as metallic solutions in water +are. + +This circumstance, in which all the experiments on metallic reduction +detailed in this essay exactly coincide, merits particular attention, +and shows that the manner, in which combustible bodies effect the +reduction, is the same in them all. + +7. When one body is oxygenated, another, at least, is restored at +the same time to its combustible state; and _v. v._ when one body is +restored to its combustible state, another at least is at the same time +oxygenated. + +8. Quantities of air, and water, equal to those decomposed in the +different species of combustion, are constantly a forming. + +Thus nature, by maintaining this balance of power between combustible +and oxygenated bodies, prevents the return of original chaos. + +Since then in every act of combustion, one body, at least, is +oxygenated, and another restored, at the same time, to its combustible +state, the phenomena of combustion may be referred to two heads, viz. + +_Oxygenation_, or the union of oxygen with combustible bodies, and + +_Reduction_, or the restoration of oxygenated bodies to their +combustible state. + +And since in every instance of combustion water is decomposed, and one +body oxygenated by the oxygen of the water, while another is restored +to its combustible state by the hydrogen of the same fluid, it follows, + +1. That the hydrogen of water is the only substance, that restores +bodies to their combustible state. + +2. That water is the only source of the oxygen, which oxygenates +combustible bodies. + +3. That no case of combustion is effected by a single affinity. + +This view of combustion may serve to show how nature is always the +same, and maintains her equilibrium by preserving the same quantities +of air and water on the surface of our globe: for as fast as these are +consumed in the various processes of combustion, equal quantities are +formed, and rise regenerated like the Phenix from her ashes. + + + + + NOMENCLATURE _of the Chymical Terms used in this Essay_. + + + NEW NAMES. OLD NAMES. + + Ammonia Caustic vol. alkali. + + Acetite of lead Sugar of lead. + + ---------- copper Verdirgris. + + Azote Base of phlogisticated air. + + Azotic gas Phlogisticated air. + + Alkaline sulphure Liver of sulphur. + + Alcohol Highly rectified spirit of wine. + + Carbone Pure coal. + + Carbonic acid Fixed air. + + Caloric Heat. + + Hydrogen Base of inflammable air. + + Hydrogen gas Inflammable air. + + Hydrure of sulphur A compound of hydrogen and sulphur. + + ---------- phosphorus A compound of hydrogen and + phosphorus. + + Muriate of tin Salt of Jupiter. + + ---------- silver Luna cornea. + + ---------- arsenic Arsenic combined with muriatic acid. + + ---------- zinc Marine salt of zinc. + + ---------- cobalt Marine salt of cobalt. + + Nitric acid Dephlogisticated nitrous acid. + + Nitro-muriatic acid Aqua regia. + + Nitro-muriate of gold A compound of gold and aqua regia. + + ---------------- platina A compound of platina and aqua + regia. + + Nitrate of silver Lunar nitre, crystals of the moon. + + ------- of mercury Mercurial nitre. + + ------- of bismuth Nitre of bismuth. + + ------- of manganese Nitre of manganese. + + Oxygen Base of vital air. + + Oxygen gas Vital air. + + Oxygenated muriate of mercury Corrosive sublimate. + + Prussiate of mercury A compound of mercury and prussic + acid. + + Phosphorated hydrogen gas Phosphoric air. + + Potash Caustic vegetable alkali. + + Sulphuric ether Vitriolic ether. + + Sulphureous acid gas Vol. sulphureous acid. + + Sulphurated hydrogen gas Hepatic acid. + + Sulphate of copper Blue vitriol. + + ----------- zinc White ditto. + + ----------- iron Green ditto. + + ----------- manganese Vitriol of manganese. + + Soda Caustic mineral alkali. + + Tartarite of antimony Emetic tartar. + + + FINIS. + + +FOOTNOTES: + +[1] Essay on Phlogiston, by M. Kirwan, a new edition, p. 21, and 16. + +[2] Experiments on Air and Fire. Eng. trans. p. 174. + +[3] Essay on Phlogiston, a new edition, p. 38–166. + +[4] Essay on Phlogiston, p. 207. + +[5] Essay on Phlogiston, p. 205. + +[6] Essay on Phlogiston, p. 14. + +[7] Essay on Phlogiston, p. 13–15. + +[8] _Ibid._ p. 25. and Philo. Trans. Vol. 78. p. 314. + +[9] Scheele, p. 162, French translation. + +[10] Roz. Journ. Feb. 1782. + +[11] Elective Attractions, English Translation, p. 87. + +[12] M. Monnet Dissolution de Metaux, p. 159. + +[13] Phil. Trans. Vol. 73. An. 1783. + +[14] Essay on Phlogiston, a new Edit, by M. Kirwan, p. 46. + +[15] Priestley, Vol. VI. p. 150. + +[16] Chem. Essays, Vol. III. p. 219. + +[17] M. Kirwan, Phil. Trans. for 1786. + +[18] Chem. Essay. Vol. II. p. 206 and 207. Eng. Trans. + +[19] Essay on Phlogiston, new Ed. by M. Kirwan, p. 61. + +[20] Phil. Trans. 1785. Vol. LXXV. p. 289. + +[21] El. Nat. Hist. & Chem. Eng. Trans. in three volumes, p. 163. Vol. +I. + +[22] Ess. on Phlog. a new Ed. by M. Kirwan, p. 60. + +[23] Experiments on Air and Fire, Eng. Trans. p. 82. + +[24] Commerce of the Arts. + +[25] Elec. Attrac. Eng. Tran. p. 223. + +[26] Crell’s Chem. Jour. Vol. II. p. 48. Eng. Trans. + +[27] Essay on Phlogiston, new Ed. p. 82. + +[28] Ibid. p. 122. + +[29] Elec. Attr. Eng. Trans. p. 211. + +[30] El. Att. Eng. Trans. p. 213. + +[31] Essay on Phlog. new Ed. by Mr. Kirwan, p. 233–235. + +[32] Chem. Ess. Vol. II. p. 358. Eng. Trans. + +[33] Chem Ess. Vol. II. p. 206–207. Eng. Trans. + +[34] Exper. on Air and Fire, Eng. Trans. p. 112, and 130. + +[35] Ess. on Phlog. new Ed. by Mr. Kirwan, p. 236, and 237. + +[36] Chem. Essays, Vol. II. p. 384, Eng. Trans. + + + + +TRANSCRIBER’S NOTE + + + Obvious punctuation errors have been corrected after careful + comparison with other occurrences within the text. + + Inconsistent hyphenations have been left as is. + + The tables in this book are best viewed using a monospace font. + + The original book used the character ſ (long-form s). This has been + changed to the modern s in this eBook. + + Footnotes have been renumbered consecutively and moved to the end of + the text. + + Except for those changes noted below, all misspellings in the text, + and inconsistent or archaic usage, have been retained. + + Page 28. “hygrogen” replaced by “hydrogen”. + Page 39. Unclear image of potentially “horn” replaced by “both”. + Page 48. “theprecipitate” replaced by “the precipitate”. + Page 77. “evident manmer” replaced by “evident manner”. + Page 84. “CHAPTER III” replaced by “CHAPTER IV”. + Page 88. “immediaaely” replaced by “immediately”. + Page 106. “is influence” replaced by “its influence”. + Page 156. Added full stop after “Exp. 4. Mercury” for consistency. + + Errata from the publisher has been applied as described below. + + Page viii. “ere long” replaced by “erelong”. + Page 15. “particles of reduced gold were observed” replaced by + “I observed many particles of reduced gold”. + Page 17. Removed 3 duplicated lines of text. + Page 137. “or by uniting” replaced by “nor by uniting”. + Page 163. “and the caloric” replaced by “the caloric”. + +*** END OF THE PROJECT GUTENBERG EBOOK 77630 *** |