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The photographic news
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- 35.1891
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- 1891
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1725, September 25, 1891
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September 25, 1891.] THE PHOTOGRAPHIC NEWS. with a crash that Well, I’ll take two half crowns for the lot, and allow a discount of threepence in the shilling for cash. Mrs. Crummey has been good enough to say I may have another try, but I think not. I think I’ll wait till I get a baby of my own, and when I do that you may shoot me. VOLATILE PLATINUM COMPOUNDS.* BY W. PULLINGER, BRACKENBURY SCHOLAR OF BALLIOL COLLEGE, OXFORD. Vapour Density Experiments.—These were at first con ducted in a Victor Meyer’s tube, in an atmosphere of carbon monoxide. The bottom of the bulb was lined with asbestos. A small block of the compact substance (experiments were made with both substances) was dropped directly from the stopper on to the asbestos. Experiments were made at various temperatures varying between 200° and 400”. There was, however, no agree ment between any of the results. In some cases decom position was evident, in others the substance was not completely volatilised. Some experiments were made without asbestos, but in no single case, even at a very high temperature, and after the lapse of a considerable time, was volatilisation complete. A final attempt was made with a modified form of apparatus devised by Pro fessor Lothar Meyer. The bulb of the apparatus is con stricted in the middle. A small piece of platinum gauze rests on the constricted part; the substance is dropped directly on to the gauze. The vapour formed falls at once into the lower part of the tube, leaving the atmosphere surrounding the solid unsaturated. In this manner the whole of the substance was volatilised ; but, on examining the tube, it was found that, even at a temperature of 250’, the vapour of the substance in the bottom part of the tube was decomposed in contact with the glass. The colour of the vapour is a dull red. It seemed evident that the vapour density of the compounds could not be determined when glass vessels were used. Possibly the form of apparatus described above may be useful in determining the vapour densities of other solids with heavy vapours. It was supposed possible that the corresponding bro mine derivatives might be more volatile. An attempt was therefore made to obtain them. Preparation of Platinum Dibromide.—Schiitzenberger obtained platinum dichloride by passing chlorine over heated platinum sponge. An attempt to obtain the di bromide in the same way failed. V. Meyer and Ziiblin obtained the tetrabromide by heating platinum sponge with bromine and hydrobromic acid in a sealed tube at 180°, evaporating to dryness, and heating to 180°. It is not necessary, however, to make use of sealed tubes. If platinum sponge be simply boiled for a short time with an excess of bromine and hydrobromic acid, in a flask con nected with a reflux condenser, the whole is dissolved. If the solution is then evaporated to dryness and the residue heated, bromine and hydrogen bromide are evolved. According to Topsoe, this takes place slowly at 100°, but more quickly at 200’, leaving a bright brown powder which, when washed to free it from undecomposed tetrabromide, gives a brownish-green residue of the di bromide. It is, however, very doubtful whether any di bromide is formed at the lower temperature. The residue, obtained as above, was heated in an air-bath. Some di bromide was formed at 180°. This, when thoroughly * Concluded from page 659. washed from the tetrabromide, had not a brownish-green colour, but was coal-black. After heating another por tion at 255° for five hours, some undecomposed tetra bromide still remained, but this time the colour of the dibromide was a dark, clear brown. It would seem, therefore, that the colour of the product is conditioned by the temperature of its formation. A third portion was heated at 310° for four hours in a current of air. Even at this temperature a residue of tetrabromide was left. The most convenient temperature for the prepara tion of the dibromide was found to be about 280’. It may be here mentioned that spongy platinum is also dissolved by a hot solution of iodine in hydriodic acid, yielding a dark red liquid. From this the tetraiodide can be easily obtained by evaporating it to dryness, heating the residue to 180’ in an air-bath, and washing away the soluble part. The iodide thus obtained is a compound of singular stability, seeing that it can be heated with sodium carbonate to the fusing point of that salt without losing all its iodine. A rough determination of the platinum in the iodide was made by reduction with magnesium and acetic acid ; this gave a percentage of 28'2 of platinum, against the theoretical 27 7. Action of Carbon Monoxi<le on Platinum Dibromide.—The dibromide was contained in a small boat which was placed in a combustion tube. The end of the tube was bent into a U-shape, so as to serve as a receiver for the volatile compound. The straight part of the tube was placed in a combustion furnace, which was gradually heated ; in the meantime, a slow current of dry carbon monoxide was passed over the dibromide. At the cool end of the tube a sublimate was formed, consisting of yellow and white crystals, and a brick-red powder. At about 180° the contents of the boat melted, giving a dark red liquid which was volatilised with difficulty; so great was the difficulty of completely volatilising this liquid, that it seemed impracticable to determine its vapour density. The sublimed substance was now melted by immersing the U-tube in a heated paraffin bath. A current of carbon monoxide was passed over the melted substance for more than an hour, in order that a maximum amount might be absorbed. From the analogy to the chlorine compounds, it was supposed that a compound PtBr,,2C0 would be formed. Such, however, was not the case. On cooling, the substance solidified to a mass of bright red needles. The platinum and bromine in this compound were estimated by heating a weighed quantity in a platinum crucible with a very large excess of carbonate of soda. That none of the substance was volatilised was evident from examination of the crucible after ignition. The resulting platinum was washed and weighed, and the bromine in the washings was estimated in the usual way. In this and in many other analyses the carbonate of soda was tinged a darkish blue. This may have been due to the formation of a sub-bromide of sodium, corresponding to the subchloride of potassium described by Bunsen (Ann. Phys. Chern., 1861, 113, 445). The following results were obtained :— Percentage of platinum, 50'44 50'33 ; mean, 50'38 ,, bromine, 41'504 1'03 ; ,, 41'26 „ CO, 8-06 8'67 ; „ 8'36 This approximates closely enough to the constitution of a compound having the formula PtBr„,CO, which has the following percentage composition : platinum, 50'90; bromine, 41'79 ; CO, 7'31. It would appear, therefore, that this compound, which may be called “ carbonyl-
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