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207 SCIENTIFIC AND ANALYTICAL
pared by warming distilled mercury and projecting CHEMISTRY.
sodium therein. By varying the proportion of mercury, the sodium amalgam was obtained either quite fuid,
pasty, in acicular crystals or quite hard. The ammonium Experiments with the Ammonium Amalgam, by amalgam was prepared from all of these alloys; but CHARLES M. WETHERILL, Ph.D., M.D.
when a hard amalgam was used in the experiment, the The existence of the hypothetical radical NH, depends ammonium amalgam formed upon the surface of the less upon the characteristics of its so-called amalgam lump and proceeded gradually to the inside, and the than upon the parallelism of its salts with those of the swelling was not so great at the close of the reaction. alkalies. If, from these analogies, we accept the The more fluid the sodium amalgam was, the more metallic nature of ammonium, it will be difficult to avoid readily did the swelling take place. assigning a similar character to the radicals of all of the Ex. 1. Sodium amalgam projected into dilute soluorganic bases; and especially to those which, like the tions of sulphuric or hydrochloric acids, or into an compound ammonias, have an alkaline reaction and aqueous solution of potassa, decomposes water, but not possess physical and chemical properties so like ammonia. violently. The mercury does not swell, but this pheno
If such be the inference, we must admit numerous menon takes place immediately if a little solution of salcompound metals, which exist only in certain states of ammoniac be added. It is not, therefore, merely hydrocombination of their elements. The assumption of the gen (itself a hypothetical metal), in the nascent state elementary nature of a metal is destroyed and the ideas which occasions the swelling. of the alchemists are revived; for if NĖ, be a metal and Ex. 2. Sodium amalgam in a solution of ammonia NH, be not one, why may not other metals, esteemed decomposes water without swelling ; but this phenoelements, be also compounds ?
menon ensues immediately if a drop of sulphuric or In examining the so-called ammonium amalgam one hydrochloric acid be added. Hence, hydrogen in the is interested at the great resemblance which it bears to nascent state and ammonia in the condition of stable the amalgams proper in its physical properties. The equilibrium do not produce the swelling. To effect this mercury has lost its fluidity or mobility, and, at the same the ammonia itself must also be nascent. time, its relations of cohesion and adhesion are very Ex. 3. When the ammonium amalgam is made in & sensibly altered. It no longer coheres powerfully, but test tube containing a thermometer, a rise of temperaadheres to, or wets, platinum iron and other metals, like ture of from 20 to 3° C. is indicated during the swelling. the potassium or sodium amalgam. When left to itself, The temperature falls at the completion of the swelling. the swollen mass shrinks, and gradually resolves itself If the turgidity subsides by reason of the great affinity into NH (NH,OH and Hg, because (as is usually ex- of NH, for the oxygen of the water, decomposing the plained) NH, has a great tendency to fall apart into latter with the evolution of hydrogen, an elevation of NH, and H. This explanation might be satisfactory temperature ought to be maintained until the NH has when applied to the difficulty of isolating NH,, as from become converted into NH,0. any of its salts ; but is not so in the case before us. Ex.
If a test tube be filled with a solution of sal. If ammonium falls apart thus readily in the presence ammoniac, inverted in a capsule containing the same of mercury, why does it combine with it at all to be de- salt, and a piece of sodium amalgam be introduced under composed in the very act of union ? If it be said that the test tube, the ammonium amalgam is at once genein NH Hg the NH, has so great a capacity for oxidation rated, with the constant evolution of hydrogen gas; the that it at once decomposes water, with the formation of porous amalgam floats up to the surface of the liquid, NH,0 and H; still why should NH, unite with the and, subsiding after a while, gradually returns to mermercury, which is not as near to it as, or at least no cury. From the time that the swelling is at its maxinearer than, the water ? In reflecting upon the pheno- mum until the mercury is restored to its pristine condimenon, I conceived the idea that there is really no tion, there is but trifling increase of the volume of the amalgam of ammonium formed; but, in the reaction, gas, and this increase appears to be due to the minute the sodium decomposes the water, evolving hydrogen, particles of sodium amalgam which have been brought and forming caustic soda, which in its turn sets free out of contact with the sal-ammoniac by reason of the ammonia from the chloride, the mercury being also turgescence. None of the gas in the test tube is absorbliberated. Thus
able by water; it is all hydrogen, and the sal-ammoniac NH,Cl+HO +HGNa=NH,0+H+ NaCl +Hg. remaining reacts strongly alkaline. The same phenoAt the same time the molecules of the mass are altered menon takes place when the amalgam is formed in a in their capacity for cohesion by catalysis, polarity of solution of sal-ammoniac in a capsule under a layer of atoms or some unknown cause, so that the bubbles of naphtha. The presence of air, therefore, has no part in gas are retained, and swelling takes place.
the subsidence of the swelled mass. Without the assumption of an unknown cause, the
Ex. 5. When the amalgam, having again sunk to the swelling may be accounted for by admitting that the bottom of the capsule in the last experiment, is pressed evolution of gas brings portions of the sodium amalgam with the finger against the vessel, under the naphtha, it out of contact with the solution, and the mass thus has at first a pasty or smeary nature; but, apparently remains pasty enough to retain the gas bubbles of hydro- by the expression of hydrogen gas from its pores, it is gen and ammonia for a while. The swelling may sub- very quickly restored to the ordinary condition of side by reason of the final oxidation of this residual mercury. sodium amalgam.
Ex. 6. When the ammonium amalgam is squeezed By the kindness of Professor Henry, the opportuni- through a piece of muslin, it is immediately, and without ties of the laboratory of the Smithsonian Institution change of temperature, or other evidence of affinity, were afforded me in the winter of 1863-4, to perform resolved into mercury. the following experiments upon this subject.
Ex. 7. If a drop of sal-ammoniac solution be placed The ammonium amalgams were obtained by the upon a plate of glass, a lump of soft sodium amalgam agency of the sodium amalgam, which was itself pre-l be added, and another plate of glass be pressed upon VOL. XII. No. 309. NOVEMBER 3, 1865.
Experiments with the Ammonium Amalgam.
Nov. 3, 1865.
the whole, the ammonium amalgam formed cannot swell, but not nearly to so great an extent as with oxalate of but expands laterally, assuming a reticular appearance awmonia. The globule of methylamine amalgam by reason of the many gas bubbles which in fact thus pressed between glass plates manifests a reticulated become perceptible.
appearance from gas bubbles, but to a less degree than If a lump of ammonium amalgam, already in the in the case of ammonia salts. Hydrogen and methylswollen condition, be pressed between two plates of glass, amine are evolved. it is spread out into a thin perforated film resembling Ex. 15. With the battery. The ammonium amalgam lace.
was formed by the battery, using different ammonia Ex. 8. If a piece of spongy platinum be heated and salts in contact with mercury at the negative pole. stirred into smelted sodium amalgam, the latter fills the The general characteristics of the amalgam thus pores of the platinum sponge, and coats it uniformly. A obtained were the same as when sodium was employed. piece of this compound in contact with a solution of sal- With a Smee battery of six pairs, of which each zinc ammor:iac, evolves hydrogen and ammonia, but does not plate measured 3 x 5 inches, the amalgam was obtained swell ; nor does a globule of liquid mercury, expressed in small quantities; but ten of Bunsen's elements were from the mass, exhibit any of the characters of the required to obtain sufficient to study its properties. ammonium amalgam.
By the electrolysis of a solution of sal-ammoniac conEx. 9. A piece of ammonium amalgam was wiped tained in a U-tube, which was furnished with a porous gently with filter paper and placed in naphtha. After a diaphragm of filter paper, decomposition took place little while (to permit any adherent water to be decom- rapidly with either of the batteries ; hydrogen and amposed) a test tube full of naphtha was inverted over it, monia appearing at the negative pole, and nitrogen, chlothe evolution of hydrogen gas continued as the amalgam rine, and hydrochloric acid at the positive pole. No shrank, and when, after the lapse of an hour, the mer- formation of chloride of nitrogen was detected in the cury was restored to its usual condition, a bubble of gas, reaction. equal in volume to the globule of mercury, was collected. The amalgam did not form with mercury in the nega
Ex. 10. If a drop of sodium amalgam be heated upon tive branch of the U, the decomposition then being the a glass plate, then touched with a drop of sal-ammoniac same as without the metal. solution, it at once swells to the full size of an ammo- The electrolysis of carbonate of ammonia yielded nium amalgam which would have required several similar results, carbonic acid being evolved. minutes if the reaction had taken place in the cold. With solution of nitrate of ammonia in a U tube,
Ex. 11. The sodium amalgam decomposes cold water hydrogen and ammonia appeared at the negative pole, with comparative slowness ; in boiling water a rapid and nitric acid and oxygen at the positive electrode. A evolution of gas takes place, although some time is re- small quantity of the gases collected at the positive pole quired to fully oxidise the sodium. Boiling solution of were absorbed by water. If a globule of mercury be aqua ammonia acts like boiling water. In none of these placed in a cup-like depression in a moistened lump of cases does any swelling take place, but this phenomenon Bal ammoniac or carbonate of ammonia, and be connected is manifested
immediately if to the boiling aqua ammonia with the negative pole, the circuit being completed through a few drops of carbonate of ammonia be added. the salt, the aminonium amalgam is formed while the cur
: Ex. 12. The ammonium amalgam is formed with rent is passing: apparently equal facility, employing the solutions of the If a piece of filter paper be placed upon a glass plate, following ammoniacal salts:--Chloride, oxalate, sulphate, and be moistened with a solution of carbonate of amand bi-sulphate ; the characteristics of the amalgam thus monia containing lumps of the salt, and if upon the formed being alike. The reaction with bisulphate of paper a globule of mercury be deposited, the amalgam is ammonia is instructive, showing the formation of the beautifully manifested when the current of a ten-cell amalgam in the presence of an acid which facilitates the Bunsen battery is passing through the mercury and paper, decomposition of water by certain metals. If a piece the metal being in contact with the negative pole. The of reddened litmus paper be saturated with solution of amalgam swells out in a dendritic form, tending towards bisulphate of ammonia, and a piece of sodium amalgam the positive pole and maintaining its position
while the be dropped thereupon, the formation of the ammonium current lasts. Upon breaking the connexion the swelled amalgam takes place as usual, and the evolution of the mass shrinks gradually. At all times, until restored to ammonia neutralises the acid, producing an alkaline re- the condition of mercury, the amalgam exbibits numeaction upon the paper under the mass.
rous and minute gas bubbles when pressed between glass Ex. 13. The ammonium amalgam cannot be formed plates. with solation of nitrate of ammonia. With this reagent If, during the passage of the current, a glass plate be a very rapid evolution of gas takes place, and a globule pressed upon the amalgam, it is flattened into a thin of mercury remains. In this reaction there are no indi- plate or film. By this means the swelling is prevented, cations of hyponitrous or nitrous acids, and a drop of and the ammonium amalgam is not formed. This result sulphide of ammonium added to the resulting liquid pro- appears to be conclusive as to the non-existence of the duces no colouration, except in a film upon the globule ammonium amalgam, for, if it exist, it should be mainof mercury. If a drop of fluid sodium amalgam be pro- tained in a film as well as in a globule as long as the jected into a drop of solution of sal-ammoniac upon a current is passing. glass plate, the ammonium amalgam is formed rapidly; The so-called ammonium amalgam could not be formed but a few drops of solution of nitrate of ammonia by the electrolysis of nitrate of ammonia, and a few drops poured upon the swelled mass reduce it instantly, and of a solution of this salt causes the swelling to subside in without the evolutions of nitrous fumes, to the condition ammonium amalgam already formed by the action of the of ordinary mercury.
battery upon sal-ammoniac, or carbonate of ammonia, in Ex. 14. By the kindness of M. Carey Lea, Esq., who contact with mercnry. furnished me with some of the salt, I have acted upon If spongy platinum, imbued with mercury, be placed the sodium ainalgam with solution of oxalate of methyl- in contact with the negative pole of the battery, and the amine. A slight turgescence is exhibited in this reaction, current be passed through either a solution of sal-am
Analysis of Natural Phosphates. Nov. 3, 1865.
209 moniac, or one of carbonate of ammonia to the positive ing an excess of lime (mechanically held) derived from pole, no swelling takes place, even though a large globule the carbonate of lime present in bones. This error is of mercury adhere to the sponge ; but violent ebullition to a great extent removed by redissolving the phosphate of gas is manifested.
after it has been washed, and then reprecipitating This is a very instructive experiment. The sponge of it. The determinations thus made can never be very platinum cannot act by reason of fine pores, for they are exact; they are sufficiently so, however, for some comall filled with mercury. The prevention of the amalgam mercial purposes, and the method has the advantage of formation must lie in the nature of the platinum itself; simplicity and speed. itself; it is a catalytic or contact action.
This method is wholly unfit for the analysis of coproFrom these experiments it would seem that, lites, which contain a much larger proportion of car
1. The so-called ammonium amalgam is not an alloy bonate of lime than bone-namely, about 1 part of of mercury and ammonium.
carbonate to 4 of phosphate; while in bones the propor2. The swelling of the mass in the phenomenon is due tion is 1 to 15. Besides, coprolites generally contain a to the retention of gas bubbles; and,
small quantity of fluoride of calcium-a salt insoluble 3. The coherence of the gases and liquids concerned is in water, and, therefore, precipitated with the phosphate changed from a normal condition, exhibiting phenomena of lime. The results obtained are, therefore, invariably which
too high. Thousands of tons of coprolites are, neverthe[We remember, about fifteen years ago, witnessing less, yearly purchased on the strength of such analyses ! some most interesting experiments by a talented young more than 59 or 60 per cent of phosphates are to be
Generally speaking, all analyses of coprolites showing chemist, Mr. Scarlett, on the subject of the ammonium suspected, and the buyer had better inquire what method amalgam. Mr. Scarlett, who was then a student at the of analysis has been adopted. Royal College of Chemistry, had not only discovered a II. Separation by Means of Iron.—The solution way of preserving ammonium amalgam by submerging and acetate of soda, and then boiled; the whole of the
of phosphate in acid is treated with perchloride of iron it under castor-oil
, in which it appeared quite perma- iron precipitates, taking with it all the phosphoric acid nent; but, we believe, he had succeeded in re-forming present. One of two plans is then followed. If a the amalgam, without the intervention of sodium, by known quantity of iron has been added, the precipitate the direct combination of its constituents in sealed tubes. is burnt and weighed; the amount of iron used deducted Many Fellows of the Chemical Society will doubtless leaves the amount of phosphoric acid present. Or, the recollect the interest with which Mr. Scarlett's ammo- better, ci ric acid added, and the phosphoric acid pre
precipitate is dissolved in hydrochloric acid, tartaric, or, nium amalgam, in pint bottles, was examined, at the cipitated by magnesia and ammonia. The first mode of close of one of the evening meetings in Cavendish procedure is the speedier, but cannot be followed if the Square. We believe Mr. Scarlett died soon after. Can phosphate itself contains iron or aluminium; the second any of our readers inform us if he left any record of these plan is applicable in all cases. Separation by means of valuable experiments ?—ED. C. N.]
iron is a reliable method; its successful use requires a little experience; the chief practical difficulty is the
bulk of the ferruginous precipitate. Analysis of Natural Phosphates, by R. WARINGTON, jun." III. Separation by Means of Lead.—The nitric PHOSPHORIC ACID forms insoluble compounds with of acetate of lead, and the precipitate, after warming,
acid solution of the phosphate is treated with an excess nearly all bases except alkalies. When occurring com. washed by decantation. The phosphate of lead is then bined with an alkali
, it is determined by the chemist decomposed by treatment with oxalic acid; or it is diswithout difficulty; in our manures, however, it is found solved in nitric acid, and the lead thrown down either united with lime, oxide of iron, alumina, and magnesia, with sulphuretted hydrogen or sulphuric acid.
it is when in this form of combination that its esti- thus removing the lead, the phosphoric acid is determation has given chemists so much trouble. More atten- mined with magnesia, a little citric acid being first tion and ingenuity, have perhaps been called forth by added if iron were originally present. This method is this problem than have been bestowed upon any portion of chemical analysis; the result has been the simple and good, and applicable to the analysis of all publication of a great number of excellent processes.
the phosphates employed in agriculture.
IV. Separation by Means of Tin.-The concenThe subject is a large one ; we shall mention those trated solution in nitric acid is digested with a weighed methods only which are applicable to agricultural phos- amount of pure tin foil, in quantity about eight times phates.
that of the phosphoric acid supposed to be present. The I. Estimation as Phosphate of Lime.--Attention is naturally called first to the old, and still very phoric acid ; it is collected, washed, burnt, and weighed,
precipitated binoxide of tin carries with it all the phoscommon method of precipitation by ammonia ; advantage the excess over the oxide from the tin used being is taken of the insolubility of phosphate of lime; ammonia is added to the acid solution of the phosphate ; form here described is not susceptible of the highest
phosphoric acid. This method is simple, but in the and the precipitated phosphate of lime collected and degree of accuracy. It is not available in the presence weighed. In cases where phosphate of lime occurs of much iron. associated with only alkaline salts, as in Peruvian
V. Separation by Means of Mercury.-The nitric guano, this plan leaves little to be desired; the in- acid solution is evaporated to dryness with excess of solubility of phosphate of lime is
, however, not quite metallic mercury, the residue collected and washed, mixed equal to the requirements of analysis. In applying when dry with carbonate of soda, and very, gradually this method to bone-ash, the results obtained are heated to fusion. The fused mass is dissolved in water, frequently too high; the precipitated phosphate contain- neutralised with acid, and the phosphoric acid precipi
* Extracted from “Practice with Scienco." Part 1. tated by magnesia. This method is said on high authority
Society of Arts.
Nov. 3, 1865.
to be perfectly accurate; it has not been much used for person interested in that product, is enabled to ascertain agricultural purposes.
in half an hour exactly the amount of crystallised sugar VI. Estimation as Phosphate of Uranium.- there is ir a given sample, as compared with the quantity The acetic solution is precipitated by acetate of uranium, of non-crystallisable, or what is commonly called treacle. the solution boiled, the phosphate of uranium washed by M. Duboscq Soleil's apparatus is considered so accurate
that the French Government has adopted it to determine decantation, ignited, and weighed. The method is available only when iron and aluminium are absent; customs duties are levied upon the results given by this
the value of raw sugars imported into the country, and the when properly performed it admits of great accuracy. instrument. I may further add that this apparatus, called a
vii. Separation by Means of Sulphuric Acid. “Polarising Saccharometer,” is based on the peculiar pro-The acid solution of the phosphate is evaporated with perty which light has when polarised, or when its rays excess of sulphuric acid, the whole then treated with are received at an angle of 35°25' on a plate of touralcohol, and the sulphate of lime separated by filtration. maline or a mirror. M. Duboscq Soleil's apparatus The phosphoric acid is then determined with magnesia. enables him to work with polarised light, which presents This plan is an old one, and now little used.
the various colours of the spectrum, in such a way as to VIII. Separation by Means of Oxalic Acid.-enable him thereby to determine, as I have already stated, In this method the solution, slightly acid with hydro- the amount of crystallisable sugar in any given quantity chloric acid, is treated with an excess of oxalate of am
of the article sufficiently accurately for all commercial monia, the oxalate of lime separated, and the phosphoric purposes.. acid in the filtrate determined with magnesia, citric acid
It is impossible for me, in a single lecture, to attempt to being added if iron or aluminium be present. This give you an idea of the various improvements which have method requires some experience to insure success. The been effected, even within the last two years, in the arts of safest plan is to keep the solution fairly acid during the or other processes which are due to the action of light on
photography, Talbotype, photozincography, glyphography, precipitation by oxalate of ammonia, and at last to re- sensitive surfaces ; but you will find an excellent paper on dissolve the magnesian precipitate in dilute acetic acid, the application of photography, and also of light to sensiand after separating any oxalate of lime it may contain, tive surfaces as applied to the art of engraving, in vol. xiii., to re-precipitate. With these precautions, the method is page 131, of the Journal of the Society of Arts, by Mr. perfectly reliable.
S. T. Davenport, under the heading of " Engraving and In reviewing these methods, we see that only Nos. II., Other Reproductive Art Processes. Still there are two III., and VIII., with perhaps V., can be recommended discoveries which appear to me to deserve passing noticefor the analysis of coprolite, or other phosphate contain- viz., the carbon process of Mr. Swan, and also the process ing iron and aluminium. For general purposes Nos. III., discovered by M. Villème, and now carried on in London vi., and VIII. appear to deserve most commendation. by a company, by which the operator is enabled not only
to take the photograph of a person, but to produce a
statuette giving a full representation of the figure itself, PROCEEDINGS OF SOCIETIES. and a far more accurate personification than could be pro
duced by any sculptor, and that at a cost of as many shil. SOCIETY OF ARTS.
lings as the sculptor would expect pounds. But the most important series of researches which have been made of
late years in connection with photography, and to which “On some of the most important Chemical Discoveries made 1 deem it my duty to call especial attention, are such as to within the last Troo Years."
acquire more and more importance as they are more deBy Dr. F. CRACE CALVERT, F.R.S., F.C.S.
veloped ; I therefore feel convinced that any one who will
devote his talents to the study of this particular branch of LECTURE 1.
photography will in time be amply rewarded, and of this
There can be no doubt when we consider the results Tuesday, April 4, 1865.
already obtained by the labours of only two or three genOn the Discoveries in Chemistry applied to Arts and Manu- | tlemen. I refer to the re-production of the various colours factures. In this lecture I intend to treat of chemistry of the spectrum upon sensitive surfaces. In 1838, Herapplied to the arts, and more especially to some of the schel was the first to publish a paper on the various discoreries which have been made within the last two colours which chloride of silver is susceptible of taking years. Many of these will appear to you to be incomplete, under the influence of certain coloured rays of light. Mr. but if complete they would not be new, for seldom are Robert Hunt also published in 1840 a paper referring to discoveries perfected at once. They are generally the the subject; but the most complete series of researches on result of many years' study, and of the thoughtful con- the subject of the re-production of the colours of the sideration of several men.
spectrum, and which led to a process by which several of The first part of this lecture will have reference to some the colours of the spectrum could be produced on a sensiof the applications which the laws of light have received tive surface, is due to Edmund Becquerel. The results during the last few years ; and it will, I hope, convince arrived at by this gentleman were so remarkable that they you of the necessity of every one engaged in the arts drew the attention of the whole scientific world; and the making himself acquainted with all the laws connected following is an outline of the processes which were applied with the phenomena of light, to enable him to appreciate by him to obtain this interesting result. He took a the discoveries which have been made, or to assist him in daguerreotype plate or a silver-plated one, and having improving upon those which are already known, as they dipped it in a weak solution of chlorine, or, what was still are constantly receiving the most valuable applications in better, a weak solution of hydrochloric acid, by connecting the arts and manufactures. Thus, for example, M. Donné it with the poles of a battery, the brilliant silver surface has applied the properties of light to ascertain the relative acquired different tints, passing gradually from an opaque values of milks by the amount of cream they contain, and white to a black tint. He also observed that the tint best this he effects by an instrument which he calls the lacto- suited to obtain favourable results was when the plate had scope. Duboscq Soleil has applied with great success one acquired a pearlish pink ; and although he found that the of the complicated laws of light-viz., polarised plate so prepared, when placed in the camera obscura, light-to the commercial estimation of the various qualities assumed the colours composing the spectrum, still they of sugars. By this process the sugar refiner, or any other were faint, but he remedied this defect of intensity of
tints by heating for several hours to a temperature of 950 yellow chromate of lead, the blue only reappearing. These to 100° the chlorinated plate, and then submitting it to the facts enable him to explain why, in ordinary photography, influence of the various colours composing the spectrum. the leaves of plants always appear black, and why, when he Further, in the course of his studies he made the impor- attempts to fix on his plates the colours of leaves, they tant observation that he could replace the peculiar action have a bluish hue, the yellow portion of the colour not of heat on his prepared daguerreotype plate by exposing being reproducible. it to the rays of the sun under a sheet of paper which had M. Niépce has made another series of observations which been steeped in an acid solution of sulphate of quinine. deserve notice -- viz., that when a plate, as prepared by The effect of this was that the plate of silver assumed an his process, is dipped in an alcoholic solution of substances intense white colour, nearly resembling that of paper ; susceptible of imparting a colour to flame, such, for whilst, if the protective paper had not been used, the silver example, as sti ontia, which communicates a red hue to it, plate would have gradually acquired a dark tint, and or baryta, which gives a yellowish-green colour, the prewould have lost the whole of its sensitive properties, the pared plates when exposed in the camera will assume the protective paper having the power of arresting completely same colour as the salt which they have on their surface the most refrangible rays of light, especially those which would impart to the flame of alcohol ; and if a salt of are beyond the line H of the spectrum. Notwithstanding copper be used, which has the property of communicating M. Edmond Becquerel's ardent hopes to find a method a variety of tints to the flame of alcohol, the plate also which would enable him to fix on a sensitive surface the will assume a variety of tints when exposed to the action various colours of the spectrum, still he failed, for they of light; and during a certain period of his lengthy faded immediately they were exposed to the direct rays of researches M. Niépce availed himself of this curious phelight, and could only be preserved in obscurity. But there nomenon to obtain coloured plates in the camera. They is one gentleman who deserves great praise for the extra- are not only interesting as reproductions of art, and as a ordinary perseverance which he has shown in this class of feat of extraordinary skill in the progress of photography, investigation. I mean the nephew of the discoverer of but they are especially so because in time they will lead photography, M. Niépce de Saint Victor. Although I will to methods which will enable us to communicate to our not enter here into the details of these valuable researches, little children perfect and correct views of our time, and as they can be found in the Comptes Rendus de l'Académie other interesting facts connected with the period in which des Sciences, still I may just be allowed to state that he we live. has not only by the following process obtained far more All persons interested in the progress of photography brilliant colours than those first produced by M. Becquerel, will find full details of the new processes for reproducing but has succeeded in re-producing on sensitive plates the vitrified photographic plates in vol. 60, page 1239, of the various colours of coloured surfaces, such as are presented Comptes Rendus de l'Académie des Sciences, 1865; these I by fabrics, flowers, &c., and further, he has lately been omit, as they are purely technical, and have only an so fortunate as to re-produce on his plates yellow and interest for those immediately engaged in that branch of black tints, which had resisted all previous attempts. To the photographic art. give you an idea of the facts arrived at by this gentleman, I shall now have the pleasure of calling your attention I may state that he has succeeded in so fixing upon sen- to a most important series of researches published by sitive surfaces the various colours of the spectrum, or of Professors Bunsen and Ruscoe ; but, to enable you to coloured surfaces, that they will bear the action of diffused appreciate their value, it is necessary that I should make light for several days. In fact, I have seen photographs the following remarks :- It is now well known that the which re-produce faithfully a small doll dressed up in solar spectrum is composed of three primary colours—blue, various colours, and in which even the most minute orna- yellow, and red; and, also, of four complementary or ment could be traced, and what is certainly not less inter- binary colours-viz., orange, green, indigo, and riolet. It esting was the re-production of the iridescent colours of is also known that those colours represent different prothe peacock's feather. To obtain these marvellous results, perties or qualities of that universal fluid called ether, M. Niépce de Saint Victor takes a daguerreotype, or silver- which, I may say, was generalised by Sir Isaac Newton coated plate, and dips it into a weak solution of hypo- under the name of gravitation, on which the whole of the chlorite of sodium, having a specific gravity of 1'35, until planetary system is based, and which gives to the universe it has assumed a bright pinkish hue. The plate is then its harmony and stability. This fluid is susceptible, under covered with a solution of dextrine, saturated with chlo- certain influences, as those generated by the sun, of being ride of lead ; it is then dried, and subsequently submitted set in vibration, and thus are generated heat, light, and to the action of heat, as in M. Becquerel's experiment, or chemical rays; and further, as there is no chemical action under the screen of sulphate of quinine, also referred to without a corresponding production of electricity, it follows above. The plate is then ready to be placed in the camera that electricity, as well as magnetism, may be considered obscura, and to receive the colours of the spectrum, or as a mere modification in the vibrations of the same fluid. representations of nature, such as flowers, as well as certain Therefore we may truly say that all the imponderable fluids colours produced by man. Lastly, he succeeds in increas- called Light, Electricity, Heat, Magnetism, and Force ing the stability of the colours developed on the sensitive have all the same origin-namely, the fluid called ether, surface, by covering the plate with an alcoholic solution and which, according to the nature of the vibrations, of gum benzoin, and M. Niépce gives the name of Helio-developes or renders palpable to our senses one of those chromy to this branch of photography,
fluids. In fact, I feel convinced that this unique fluid is During his lengthened researches, M. Niépce de St. not converted into those diverse fluids by special modifi. Victor has made two series of observations which I deem cations of its own vibrations, but that they only become it my duty to lay before you-viz., that he can produce manifest to our senses when it has imparted its own or with facility, on prepared plates, the binary colours of the special vibration to the particles of matter, and that it is spectrum-viz., orange, violet, indigo, and green, if those the peculiar vibration which it imparts to the molecules colours are natural; but if they are artificially produced of matter that developes in the molecules themselves such by the mixing of two of the primary colours, as red and a mode of vibration as gives birth to what we call light, yellow, or orange and blue, and yellow or blue, he cannot electricity, magnetism, heat, and force. In fact, there is reproduce the binary colour, but only one of the two no doubt, from the researches of Dr. J. P. Joule, Professors colours employed by the artisan to prepare them. Thus, William Thomson, Mayer, and others, that heat and force for example, he can reproduce the natural green of mala- are the same fluid, for Dr. Joule has given us the exact chite, and the beautiful colour known as Scheele's green, measurement of that force. He has demonstrated that but he cannot do so with a mixture of Prussian-blue and the amount of heat necessary to raise one pound of water