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SCIENTIFIC AND ANALYTICAL CHEMISTRY.

Experiments with the Ammonium Amalgam, by CHARLES M. WETHERILL, Ph.D., M.D. THE existence of the hypothetical radical NH, depends less upon the characteristics of its so-called amalgam than upon the parallelism of its salts with those of the alkalies. If, from these analogies, we accept the metallic nature of ammonium, it will be difficult to avoid assigning a similar character to the radicals of all of the organic bases; and especially to those which, like the compound ammonias, have an alkaline reaction and possess physical and chemical properties so like ammonia. If such be the inference, we must admit numerous compound metals, which exist only in certain states of combination of their elements. The assumption of the elementary nature of a metal is destroyed and the ideas of the alchemists are revived; for if NH, be a metal and NH, be not one, why may not other metals, esteemed elements, be also compounds?

In examining the so-called ammonium amalgam one is interested at the great resemblance which it bears to the amalgams proper in its physical properties. The mercury has lost its fluidity or mobility, and, at the same time, its relations of cohesion and adhesion are very sensibly altered. It no longer coheres powerfully, but adheres to, or wets, platinum iron and other metals, like the potassium or sodium amalgam. When left to itself, the swollen mass shrinks, and gradually resolves itself into NH (NHO)H and Hg, because (as is usually explained) NH has a great tendency to fall apart into NH, and H. This explanation might be satisfactory when applied to the difficulty of isolating NH, as from any of its salts; but is not so in the case before us.

If ammonium falls apart thus readily in the presence of mercury, why does it combine with it at all to be decomposed in the very act of union? If it be said that in NH,Hg the NH, has so great a capacity for oxidation that it at once decomposes water, with the formation of NH,O and H; still why should NH, unite with the mercury, which is not as near to it as, or at least no nearer than, the water? In reflecting upon the phenomenon, I conceived the idea that there is really no amalgam of ammonium formed; but, in the reaction, the sodium decomposes the water, evolving hydrogen, and forming caustic soda, which in its turn sets free ammonia from the chloride, the mercury being also liberated. Thus

=

NH4Cl + HO+HGNa NH2O+H+NaCl + Hg. At the same time the molecules of the mass are altered in their capacity for cohesion by catalysis, polarity of atoms or some unknown cause, so that the bubbles of gas are retained, and swelling takes place.

Without the assumption of an unknown cause, the swelling may be accounted for by admitting that the evolution of gas brings portions of the sodium amalgam out of contact with the solution, and the mass thus remains pasty enough to retain the gas bubbles of hydrogen and ammonia for a while. The swelling may subside by reason of the final oxidation of this residual sodium amalgam.

By the kindness of Professor Henry, the opportunities of the laboratory of the Smithsonian Institution were afforded me in the winter of 1863-4, to perform the following experiments upon this subject.

The ammonium amalgams were obtained by the agency of the sodium amalgam, which was itself preVOL. XII. No. 309.-NOVEMBER 3, 1865.

pared by warming distilled mercury and projecting sodium therein. By varying the proportion of mercury, the sodium amalgam was obtained either quite fluid, pasty, in acicular crystals or quite hard. The ammonium amalgam was prepared from all of these alloys; but when a hard amalgam was used in the experiment, the ammonium amalgam formed upon the surface of the lump and proceeded gradually to the inside, and the swelling was not so great at the close of the reaction. The more fluid the sodium amalgam was, the more readily did the swelling take place.

Ex. 1. Sodium amalgam projected into dilute solutions of sulphuric or hydrochloric acids, or into an aqueous solution of potassa, decomposes water, but not violently. The mercury does not swell, but this phenomenon takes place immediately if a little solution of salammoniac be added. It is not, therefore, merely hydrogen (itself a hypothetical metal), in the nascent state which occasions the swelling.

Ex. 2. Sodium amalgam in a solution of ammonia decomposes water without swelling; but this phenomenon ensues immediately if a drop of sulphuric or hydrochloric acid be added. Hence, hydrogen in the nascent state and ammonia in the condition of stable equilibrium do not produce the swelling. To effect this the ammonia itself must also be nascent.

Ex. 3. When the ammonium amalgam is made in a test tube containing a thermometer, a rise of temperature of from 2° to 3° C. is indicated during the swelling. The temperature falls at the completion of the swelling. If the turgidity subsides by reason of the great affinity of NH, for the oxygen of the water, decomposing the latter with the evolution of hydrogen, an elevation of temperature ought to be maintained until the NH has become converted into NH10.

Ex. 4. If a test tube be filled with a solution of salammoniac, inverted in a capsule containing the same salt, and a piece of sodium amalgam be introduced under the test tube, the ammonium amalgam is at once generated, with the constant evolution of hydrogen gas; the porous amalgam floats up to the surface of the liquid, and, subsiding after a while, gradually returns to mercury. From the time that the swelling is at its maximum until the mercury is restored to its pristine condition, there is but trifling increase of the volume of the gas, and this increase appears to be due to the minute particles of sodium amalgam which have been brought out of contact with the sal-ammoniac by reason of the turgescence. None of the gas in the test tube is absorbable by water; it is all hydrogen, and the sal-ammoniac remaining reacts strongly alkaline. The same phenomenon takes place when the amalgam is formed in a solution of sal-ammoniac in a capsule under a layer of naphtha. The presence of air, therefore, has no part in the subsidence of the swelled mass.

Ex. 5. When the amalgam, having again sunk to the bottom of the capsule in the last experiment, is pressed with the finger against the vessel, under the naphtha, it has at first a pasty or smeary nature; but, apparently by the expression of hydrogen gas from its pores, it is very quickly restored to the ordinary condition of mercury.

Ex. 6. When the ammonium amalgam is squeezed through a piece of muslin, it is immediately, and without change of temperature, or other evidence of affinity, resolved into mercury.

Ex. 7. If a drop of sal-ammoniac solution be placed upon a plate of glass, a lump of soft sodium amalgam be added, and another plate of glass be pressed upon

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the whole, the ammonium amalgam formed cannot swell, but expands laterally, assuming a reticular appearance by reason of the many gas bubbles which in fact thus become perceptible.

If a lump of ammonium amalgam, already in the swollen condition, be pressed between two plates of glass, it is spread out into a thin perforated film resembling lace.

Ex. 8. If a piece of spongy platinum be heated and stirred into smelted sodium amalgam, the latter fills the pores of the platinum sponge, and coats it uniformly. A piece of this compound in contact with a solution of salammor.iac, evolves hydrogen and ammonia, but does not swell; nor does a globule of liquid mercury, expressed from the mass, exhibit any of the characters of the ammonium amalgam.

Ex. 9. A piece of ammonium amalgam was wiped gently with filter paper and placed in naphtha. After a little while (to permit any adherent water to be decomposed) a test tube full of naphtha was inverted over it, the evolution of hydrogen gas continued as the amalgam shrank, and when, after the lapse of an hour, the mercury was restored to its usual condition, a bubble of gas, equal in volume to the globule of mercury, was collected. Ex. 10. If a drop of sodium amalgam be heated upon a glass plate, then touched with a drop of sal-ammoniac solution, it at once swells to the full size of an ammonium amalgam which would have required several minutes if the reaction had taken place in the cold.

Ex. 11. The sodium amalgam decomposes cold water with comparative slowness; in boiling water a rapid evolution of gas takes place, although some time is required to fully oxidise the sodium. Boiling solution of aqua ammonia acts like boiling water. In none of these cases does any swelling take place, but this phenomenon is manifested immediately if to the boiling aqua ammonia a few drops of carbonate of ammonia be added.

Ex. 12. The ammonium amalgam is formed with apparently equal facility, employing the solutions of the following ammoniacal salts:-Chloride, oxalate, sulphate, and bi-sulphate; the characteristics of the amalgam thus formed being alike. The reaction with bisulphate of ammonia is instructive, showing the formation of the amalgam in the presence of an acid which facilitates the decomposition of water by certain metals. If a piece of reddened litmus paper be saturated with solution of bisulphate of ammonia, and a piece of sodium amalgam be dropped thereupon, the formation of the ammonium amalgam takes place as usual, and the evolution of the ammonia neutralises the acid, producing an alkaline reaction upon the paper under the mass.

Ex. 13. The ammonium amalgam cannot be formed with solution of nitrate of ammonia. With this reagent a very rapid evolution of gas takes place, and a globule of mercury remains. In this reaction there are no indications of hyponitrous or nitrous acids, and a drop of sulphide of ammonium added to the resulting liquid produces no colouration, except in a film upon the globule of mercury. If a drop of fluid sodium amalgam be projected into a drop of solution of sal-ammoniac upon a glass plate, the ammonium amalgam is formed rapidly; but a few drops of solution of nitrate of ammonia poured upon the swelled mass reduce it instantly, and without the evolutions of nitrous fumes, to the condition of ordinary mercury.

Ex. 14. By the kindness of M. Carey Lea, Esq., who furnished me with some of the salt, I have acted upon the sodium amalgam with solution of oxalate of methylamine. A slight turgescence is exhibited in this reaction,

but not nearly to so great an extent as with oxalate of ammonia. The globule of methylamine amalgam pressed between glass plates manifests a reticulated appearance from gas bubbles, but to a less degree than in the case of ammonia salts. Hydrogen and methylamine are evolved.

Ex. 15. With the battery.-The ammonium amalgam was formed by the battery, using different ammonia salts in contact with mercury at the negative pole. The general characteristics of the amalgam thus obtained were the same as when sodium was employed. With a Smee battery of six pairs, of which each zinc plate measured 3× 5 inches, the amalgam was obtained in small quantities; but ten of Bunsen's elements were required to obtain sufficient to study its properties.

By the electrolysis of a solution of sal-ammoniac contained in a U-tube, which was furnished with a porous diaphragm of filter paper, decomposition took place rapidly with either of the batteries; hydrogen and ammonia appearing at the negative pole, and nitrogen, chlorine, and hydrochloric acid at the positive pole. No formation of chloride of nitrogen was detected in the reaction.

The amalgam did not form with mercury in the negative branch of the U, the decomposition then being the same as without the metal.

The electrolysis of carbonate of ammonia yielded similar results, carbonic acid being evolved.

With solution of nitrate of ammonia in a U tube, hydrogen and ammonia appeared at the negative pole, and nitric acid and oxygen at the positive electrode. A small quantity of the gases collected at the positive pole were absorbed by water. If a globule of mercury be placed in a cup-like depression in a moistened lump of sal ammoniac or carbonate of ammonia, and be connected with the negative pole, the circuit being completed through the salt, the ammonium amalgam is formed while the current is passing.

If a piece of filter paper be placed upon a glass plate, and be moistened with a solution of carbonate of ammonia containing lumps of the salt, and if upon the paper a globule of mercury be deposited, the amalgam is beautifully manifested when the current of a ten-cell Bunsen battery is passing through the mercury and paper, the metal being in contact with the negative pole. The amalgam swells out in a dendritic form, tending towards the positive pole and maintaining its position while the current lasts. Upon breaking the connexion the swelled mass shrinks gradually. At all times, until restored to the condition of mercury, the amalgam exhibits numerous and minute gas bubbles when pressed between glass plates.

If, during the passage of the current, a glass plate be pressed upon the amalgam, it is flattened into a thin plate or film. By this means the swelling is prevented, and the ammonium amalgam is not formed. This result appears to be conclusive as to the non-existence of the ammonium amalgam, for, if it exist, it should be maintained in a film as well as in a globule as long as the current is passing.

The so-called ammonium amalgam could not be formed by the electrolysis of nitrate of ammonia, and a few drops of a solution of this salt causes the swelling to subside in ammonium amalgam already formed by the action of the battery upon sal-ammoniac, or carbonate of ammonia, in contact with mercury.

If spongy platinum, imbued with mercury, be placed in contact with the negative pole of the battery, and the current be passed through either a solution of sal-am

moniac, or one of carbonate of ammonia to the positive pole, no swelling takes place, even though a large globule of mercury adhere to the sponge; but violent ebullition of gas is manifested.

This is a very instructive experiment. The sponge of platinum cannot act by reason of fine pores, for they are all filled with mercury. The prevention of the amalgam formation must lie in the nature of the platinum itself; itself; it is a catalytic or contact action.

From these experiments it would seem that1. The so-called ammonium amalgam is not an alloy of mercury and ammonium.

2. The swelling of the mass in the phenomenon is due to the retention of gas bubbles; and,

3. The coherence of the gases and liquids concerned is changed from a normal condition, exhibiting phenomena which may be classed with those of catalysis.

ing an excess of lime (mechanically held) derived from the carbonate of lime present in bones. This error is to a great extent removed by redissolving the phosphate after it has been washed, and then reprecipitating it. The determinations thus made can never be very exact; they are sufficiently so, however, for some commercial purposes, and the method has the advantage of simplicity and speed.

This method is wholly unfit for the analysis of coprolites, which contain a much larger proportion of carbonate of lime than bone-namely, about part of carbonate to 4 of phosphate; while in bones the proportion is 1 to 15. Besides, coprolites generally contain a small quantity of fluoride of calcium-a salt insoluble in water, and, therefore, precipitated with the phosphate of lime. The results obtained are, therefore, invariably too high. Thousands of tons of coprolites are, nevertheless, yearly purchased on the strength of such analyses! more than 59 or 60 per cent. of phosphates are to be Generally speaking, all analyses of coprolites showing suspected, and the buyer had better inquire what method of analysis has been adopted.

II. Separation by Means of Iron.-The solution of phosphate in acid is treated with perchloride of iron and acetate of soda, and then boiled; the whole of the

[We remember, about fifteen years ago, witnessing some most interesting experiments by a talented young chemist, Mr. Scarlett, on the subject of the ammonium amalgam. Mr. Scarlett, who was then a student at the Royal College of Chemistry, had not only discovered a way of preserving ammonium amalgam by submerging 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 the amalgam, without the intervention of sodium, by the direct combination of its constituents in sealed tubes. Many Fellows of the Chemical Society will doubtless recollect the interest with which Mr. Scarlett's ammonium amalgam, in pint bottles, was examined, at the close of one of the evening meetings in Cavendish Square. We believe Mr. Scarlett died soon after. Can any of our readers inform us if he left any record of these valuable experiments?-ED. C. N.]

Analysis of Natural Phosphates, by R. WARINGTON, jun. PHOSPHORIC ACID forms insoluble compounds with nearly all bases except alkalies. When occurring combined with an alkali, it is determined by the chemist without difficulty; in our manures, however, it is found united with lime, oxide of iron, alumina, and magnesia, and it is when in this form of combination that its estimation has given chemists so much trouble. More attention and ingenuity have perhaps been called forth by this problem than have been bestowed upon any other portion of chemical analysis; the result has been the publication of a great number of excellent processes. The subject is a large one; we shall mention those methods only which are applicable to agricultural phosphates.

I. Estimation as Phosphate of Lime.-Atten

present. One of two plans is then followed. If a known quantity of iron has been added, the precipitate is burnt and weighed; the amount of iron used deducted leaves the amount of phosphoric acid present. Or, the better, ci ric acid added, and the phosphoric acid preprecipitate is dissolved in hydrochloric acid, tartaric, or, cipitated by magnesia and ammonia. The first mode of procedure is the speedier, but cannot be followed if the phosphate itself contains iron or aluminium; the second plan is applicable in all cases. Separation by means of iron is a reliable method; its successful use requires a little experience; the chief practical difficulty is the bulk of the ferruginous precipitate.

III. Separation by Means of Lead.-The nitric

After

acid solution of the phosphate is treated with an excess
of acetate of lead, and the precipitate, after warming,
washed by decantation. The phosphate of lead is then
decomposed by treatment with oxalic acid; or it is dis-
solved in nitric acid, and the lead thrown down either
with sulphuretted hydrogen or sulphuric acid.
thus removing the lead, the phosphoric acid is deter-
mined with magnesia, a little citric acid being first
added if iron were originally present. This method is
simple and good, and applicable to the analysis of all
the phosphates employed in agriculture.

IV. Separation by Means of Tin.-The concentrated solution in nitric acid is digested with a weighed amount of pure tin foil, in quantity about eight times that of the phosphoric acid supposed to be present. The phoric acid; it is collected, washed, burnt, and weighed, precipitated binoxide of tin carries with it all the phosthe excess over the oxide from the tin used being phosphoric acid. This method is simple, but in the form here described is not susceptible of the highest degree of accuracy. It is not available in the presence

of much iron.

tion is naturally called first to the old, and still very common method of precipitation by ammonia; advantage is taken of the insolubility of phosphate of lime; ammonia is added to the acid solution of the phosphate; and the precipitated phosphate of lime collected and weighed. In cases where phosphate of lime occurs 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 precipitated by magnesia. This method is said on high authority

• Extracted from "Practice with Science." Part 1.

VI. Estimation as Phosphate of Uranium.—

The acetic solution is precipitated by acetate of uranium, the solution boiled, the phosphate of uranium washed by decantation, ignited, and weighed. The method is available only when iron and aluminium are absent; when properly performed it admits of great accuracy.

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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 there is in a given sample, as compared with the quantity of non-crystallisable, or what is commonly called treacle. that the French Government has adopted it to determine M. Duboscq Soleil's apparatus is considered so accurate the value of raw sugars imported into the country, and the customs duties are levied upon the results given by this instrument. I may further add that this apparatus, called a Polarising Saccharometer," is based on the peculiar property which light has when polarised, or when its rays are received at an angle of 35°25′ on a plate of tourmaline or a mirror. M. Duboscq Soleil's apparatus enables him to work with polarised light, which presents the various colours of the spectrum, in such a way as to enable him thereby to determine, as I have already stated, the amount of crystallisable sugar in any given quantity of the article sufficiently accurately for all commercial purposes.

VII. Separation by Means of Sulphuric Acid. -The acid solution of the phosphate is evaporated with excess of sulphuric acid, the whole then treated with alcohol, and the sulphate of lime separated by filtration. The phosphoric acid is then determined with magnesia. This plan is an old one, and now little used.

The

VIII. Separation by Means of Oxalic Acid.— In this method the solution, slightly acid with hydrochloric acid, is treated with an excess of oxalate of ammonia, the oxalate of lime separated, and the phosphoric acid in the filtrate determined with magnesia, citric acid being added if iron or aluminium be present. This method requires some experience to insure success. safest plan is to keep the solution fairly acid during the precipitation by oxalate of ammonia, and at last to redissolve the magnesian precipitate in dilute acetic acid, and after separating any oxalate of lime it may contain, to re-precipitate. With these precautions, the method is perfectly reliable.

In reviewing these methods, we see that only Nos. II., III., and VIII., with perhaps V., can be recommended for the analysis of coprolite, or other phosphate containing iron and aluminium. For general purposes Nos. III., VI., and VIII. appear to deserve most commendation.

PROCEEDINGS OF SOCIETIES.

SOCIETY OF ARTS.

CANTOR LECTURES.

It is impossible for me, in a single lecture, to attempt to give you an idea of the various improvements which have been effected, even within the last two years, in the arts of photography, Talbotype, photozincography, glyphography, or other processes which are due to the action of light on sensitive surfaces; but you will find an excellent paper on the application of photography, and also of light to sensitive surfaces as applied to the art of engraving, in vol. xiii., page 131, of the Journal of the Society of Arts, by Mr. S. T. Davenport, under the heading of "Engraving and Still there are two other Reproductive Art Processes." discoveries which appear to me to deserve passing noticeviz., the carbon process of Mr. Swan, and also the process discovered by M. Villème, and now carried on in London 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, and a far more accurate personification than could be produced by any sculptor, and that at a cost of as many shillings 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 I deem it my duty to call especial attention, are such as to

within the last Two Years."

By Dr. F. CRACE CALVERT, F.R.S., F.C.S.

LECTURE I.

Tuesday, April 4, 1865.

On the Discoveries in Chemistry applied to Arts and Manufactures. In this lecture I intend to treat of chemistry applied to the arts, and more especially to some of the discoveries which have been made within the last two years. Many of these will appear to you to be incomplete, but if complete they would not be new, for seldom are discoveries perfected at once. They are generally the result of many years' study, and of the thoughtful consideration of several men.

The first part of this lecture will have reference to some of the applications which the laws of light have received during the last few years; and it will, I hope, convince you of the necessity of every one engaged in the arts making himself acquainted with all the laws connected with the phenomena of light, to enable him to appreciate the discoveries which have been made, or to assist him in improving upon those which are already known, as they are constantly receiving the most valuable applications in the arts and manufactures. Thus, for example, M. Donné has applied the properties of light to ascertain the relative values of milks by the amount of cream they contain, and this he effects by an instrument which he calls the lactoscope. Duboscq Soleil has applied with great success one of the most complicated laws of light-viz., polarised light-to the commercial estimation of the various qualities of sugars. By this process the sugar refiner, or any other

acquire more and more importance as they are more de-
veloped; I therefore feel convinced that any one who will
devote his talents to the study of this particular branch of
photography will in time be amply rewarded, and of this
there can be no doubt when we consider the results
already obtained by the labours of only two or three gen-
tlemen. I refer to the re-production of the various colours
of the spectrum upon sensitive surfaces. In 1838, Her-
schel was the first to publish a paper on the various
colours which chloride of silver is susceptible of taking
under the influence of certain coloured rays of light. Mr.
Robert Hunt also published in 1840 a paper referring to
the subject; but the most complete series of researches on
the subject of the re-production of the colours of the
spectrum, and which led to a process by which several of
the colours of the spectrum could be produced on a sensi-
tive surface, is due to Edmund Becquerel. The results
arrived at by this gentleman were so remarkable that they
drew the attention of the whole scientific world; and the
following is an outline of the processes which were applied
by him to obtain this interesting result.
He took a
daguerreotype plate or a silver-plated one, and having
dipped it in a weak solution of chlorine, or, what was still
better, a weak solution of hydrochloric acid, by connecting
it with the poles of a battery, the brilliant silver surface
acquired different tints, passing gradually from an opaque
white to a black tint. He also observed that the tint best
suited to obtain favourable results was when the plate had
acquired a pearlish pink; and although he found that the
plate so prepared, when placed in the camera obscura,
assumed the colours composing the spectrum, still they
were faint, but he remedied this defect of intensity of

yellow chromate of lead, the blue only reappearing. These facts enable him to explain why, in ordinary photography, the leaves of plants always appear black, and why, when he attempts to fix on his plates the colours of leaves, they have a bluish hue, the yellow portion of the colour not being reproducible.

M. Niépce has made another series of observations which deserve notice-viz., that when a plate, as prepared by his process, is dipped in an alcoholic solution of substances susceptible of imparting a colour to flame, such, for example, as strontia, which communicates a red hue to it, or baryta, which gives a yellowish-green colour, the prepared plates when exposed in the camera will assume the same colour as the salt which they have on their surface would impart to the flame of alcohol; and if a salt of copper be used, which has the property of communicating a variety of tints to the flame of alcohol, the plate also will assume a variety of tints when exposed to the action of light; and during a certain period of his lengthy researches M. Niépce availed himself of this curious phenomenon to obtain coloured plates in the camera. They are not only interesting as reproductions of art, and as a feat of extraordinary skill in the progress of photography, but they are especially so because in time they will lead to methods which will enable us to communicate to our little children perfect and correct views of our time, and other interesting facts connected with the period in which we live.

All persons interested in the progress of photography will find full details of the new processes for reproducing vitrified photographic plates in vol. 60, page 1239, of the Comptes Rendus de l'Académie des Sciences, 1865; these I omit, as they are purely technical, and have only an interest for those immediately engaged in that branch of the photographic art.

tints by heating for several hours to a temperature of 95° to 100° the chlorinated plate, and then submitting it to the influence of the various colours composing the spectrum. Further, in the course of his studies he made the important observation that he could replace the peculiar action of heat on his prepared daguerreotype plate by exposing it to the rays of the sun under a sheet of paper which had been steeped in an acid solution of sulphate of quinine. The effect of this was that the plate of silver assumed an intense white colour, nearly resembling that of paper; whilst, if the protective paper had not been used, the silver plate would have gradually acquired a dark tint, and would have lost the whole of its sensitive properties, the protective paper having the power of arresting completely the most refrangible rays of light, especially those which are beyond the line H of the spectrum. Notwithstanding M. Edmond Becquerel's ardent hopes to find a method which would enable him to fix on a sensitive surface the various colours of the spectrum, still he failed, for they faded immediately they were exposed to the direct rays of light, and could only be preserved in obscurity. But there is one gentleman who deserves great praise for the extraordinary perseverance which he has shown in this class of investigation. I mean the nephew of the discoverer of photography, M. Niépce de Saint Victor. Although I will not enter here into the details of these valuable researches, as they can be found in the Comptes Rendus de l'Académie des Sciences, still I may just be allowed to state that he has not only by the following process obtained far more brilliant colours than those first produced by M. Becquerel, but has succeeded in re-producing on sensitive plates the various colours of coloured surfaces, such as are presented by fabrics, flowers, &c., and further, he has lately been so fortunate as to re-produce on his plates yellow and black tints, which had resisted all previous attempts. To 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 Roscoe; 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 violet. 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 135, 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 not converted into those diverse fluids by special modifications of its own vibrations, but that they only become manifest to our senses when it has imparted its own or special vibration to the particles of matter, and that it is the peculiar vibration which it imparts to the molecules of matter that developes in the molecules themselves such a mode of vibration as gives birth to what we call light, electricity, magnetism, heat, and force. In fact, there is no doubt, from the researches of Dr. J. P. Joule, Professors William Thomson, Mayer, and others, that heat and force are the same fluid, for Dr. Joule has given us the exact measurement of that force. He has demonstrated that the amount of heat necessary to raise one pound of water

During his lengthened researches, M. Niépce de St. Victor has made two series of observations which I deem it my duty to lay before you-viz., that he can produce with facility, on prepared plates, the binary colours of the spectrum-viz., orange, violet, indigo, and green, if those colours are natural; but if they are artificially produced by the mixing of two of the primary colours, as red and yellow, or orange and blue, and yellow or blue, he cannot reproduce the binary colour, but only one of the two colours employed by the artisan to prepare them. Thus, for example, he can reproduce the natural green of malachite, and the beautiful colour known as Scheele's green, but he cannot do so with a mixture of Prussian-blue and

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