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The photographic news
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- 35.1891
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- No. 1715, July 17, 1891
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the solution contained 1 mol. to 3 of thiocarbamide, using be accounted for in the fact that his father, Sir Wm. carbamide.—The earliest small experiment made ■with the salt and amide seemed to indicate that a tetrathiocarbamide compound was formed, but when the work was repeated on a larger scale, and the product slowly separated from alcoholic solution, it was not found possible to obtain a THE PHOTOGRAPHIC WORK OF HERSCHEL AND FOX TALBOT.* BY WILLIAM LANG, JUN., F.C.S. The two scientists whose photographic work is dealt with the usual conditions of the series of experiments. In all hold our present Photographic Convention may be de cases free amine separated along with any substance scribed as direct and indirect. Talbot’s connection was produced. essentially a direct one, living as he did within a short The proportion of bromide was then increased so that distance of Bath. Herschel’s, on the other hand, has to in the following communication were virtually contem- definite compound with 4 mols. of thiocarbamide under poraries, and their connection with the town in which we In the first number of the Edinburgh Philosophical with some more thio carbamide. 0-2222 0'126 AgBr. 0'2798 The two sets of crystals represent the compound (H 1 N 2 CS) 3 (C 2 H 5 ) 3 HNBr in somewhat different states of (To be continued-') when absolute alcohol was used, some thiocarbamide separated from the mother liquor ; gradual decomposition was found to follow further attempts at complete purifica- Herschel, resided here for several years before his appoint ment as private astronomer to George III. necessitated his removal to Slough, in the neighbourhood of Windsor. To the student, therefore, of the history of photography, Bath will have something more than a passing interest for him—it will be for ever classic ground. I only wish that the summarising of the work done by Herschel and Fox Talbot had been placed in worthier hands than mine, but having been entrusted with the task I shall do my best to Theory. 23'41 p. o. 19'51 „ B crystals. 23'28 p. c. 19'16 „ A crystals. 22'7 p. c. 20'7 „ approximately, 2 : 5, slow recrystallisation failed to give \ Journal, which made its appearance in June, 1819, the the original substance, but, instead, two distinct forms second contribution we find to be from Herschel, and its These, indi- In the memoir these salts, at all events the more important, cated by A below, were analysed with the following have their properties described. The action of hypo sulphite of soda and of the corresponding salt of potash on chloride of silver is distinctly set forth. Referring to showed that they were all of the same kind, and the ratio acquit myself of it. of bromine to sulphur in them proved to be 1 : 2'58 or, 1 tion. The crystals were analysed as under :— 0'25 gram gave 0'4247 BaSO 4 . 14 grams of the latter, and the materials were heated with absolute alcohol to the boiling point of the latter for three hours. When the liquid was allowed to cool, groups of silky crystals separated, which closely resembled the ammonium bromide compound. These were quickly drained off, washed with cold alcohol, pressed, and dried. The mother liquor, on standing over night, gave some more needles and a small crop of thiocarbamide crystals. Although microscopic examination of the silky crystals The rhomboidal crystals which separated in small quan tity along with the above, when washed with alcohol and recrystallised, were obtained in short prisms, and consist of the compound (H 1 N 2 CS)XC 2 H 6 ) 3 HNBr. 0'1532 gram gave 0'089 gram AgBr == 24'72 per cent. Br. Theory for the above compound requires 23'91 percent, of Br. The mother liquor ultimately afforded a few fine, large prisms mixed with crystals of the other types, which were richer still in bromine, but the quantity of the material obtained was too small to admit of satisfactory purification for analysis. were obtained—one portion consisting of groups of rather title “ On the Hyposulphurous Acid and its Compounds.’’ long prisms, resembling nitre in appearance, and the other In the opening sentence we are told that the experiments of somewhat large, modified rhomboids; the latter were about to be described are the result of an accident. Ex in smaller proportion and separated out more slowly, along perimenting with sulphite of lime, and noticing a bitter- ness in the liquid when almost wholly decomposed similar The nitre-like crystals were separated, as far as possible, I to that of Epsom salts, and which could not be accounted by picking and concentration of the liquids; they were for, Herschel was led to examine the properties of the body redissolved in as small a quantity of strong alcohol as pos- giving this characteristic bitterness, and which Herschel Bible (as a large proportion of hot alcohol seemed to partly showed to be hyposulphite of lime. From the hypo- decompose the compound), and the crystals were again sulphite thus produced, other hyposulphites were prepared, obtained, but in groups of smaller needles. — 8 - - • ' " " ’ • -- results:— 0 2490 gram gave 0'4118 gram BasO,. 0'1081 „ AgBr. purity, thus:— S ... Br ... the soda salt, we find it stated in the memoir, “Muriate When again crystallised from alcohol, a purer specimen of silver, newly precipitated, dissolves in this salt when in of shorter crystals, marked B, was obtained; but even a somewhat concentrated solution in large quantity, and almost as readily as sugar in water.” Herschel states it broadly that all liquid hyposulphites dissolve muriate, or, as we call it now, chloride of silver. He points out the fact that such a solution possesses great sweetness to the taste, and that most of the ordinary tests for silver fail to show the presence of that metal in the solution. He further shows that zinc can separate metallic silver on being immersed in the hyposulphite solution. In con clusion, it may be noted that the contribution is dated Slough, January 8th, 1819. Herschel had evidently found congenial work in tracing out further reactions connected with the hyposulphites. In the same volume of the Edinburgh Philosophical Journal occurs another contribution—additional facts relative to the hyposulphurous acid. This appeared in the October issue, and the date affixed to the article is 15th May, 1819. Time fails us to refer in detail to the various facts brought forward, but one observation deserves to be noted—viz., that where silver iodide is described as sparingly soluble in hyposulphites. It has to be remem bered silver bromide was then unknown. Bromine not being discovered till 1826, the salts of silver thus treated 1 by Herschel were chloride, carbonate, phosphate, borate, I lna ^ a ^ c i sulphite, and arseniate. The second volume of * Bead at the Photographic Convention.
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