552 Progress in Science. [Odtober, 



fulfils these conditions, and is, consequently, very perfect ; in practice it will 

 be found very useful. It is obtained by dissolving in distilled water equal 

 weights of sulphocyanide of ammonium and of bisulphite of ammonia. This 

 mixture keeps well, and can be used several months after its preparation, pro- 

 viding it is not left exposed to the air for any length of time ; but, should a 

 slight alteration take place in its composition, this would be of no consequence. 

 When added to a solution containing copper, it immediately precipitates 

 white sub-sulphocyanide of copper as an insoluble powder readily washed, 

 whilst it precipitates scarcely any other metal which may be present. 



The difficulty in burning off organic matter has often been experienced by 

 analytical chemists, especially when the substance under incineration yields a 

 readily fusible ash. M. A. Bechamp has proposed the use of nitrate of 

 bismuth in the state of an aqueous solution of known strength to be mixed 

 with the material to be incinerated, provided the water contained in the sub- 

 stance has been previously ascertained by drying at ioo°. The nitrate of 

 bismuth solution (the bulk thereof to ignite and calcine readily 100 to isogrms. 

 of substance should contain from 3 to 4 grms. of oxide of bismuth) having been 

 mixed with a fresh and weighed portion of the substance (yeast is taken in 

 illustration, as it is well known that this is very difficult to burn off com- 

 pletely), the mixture is first dried gently on a water-bath, next heated on a 

 sand-bath hot enough to cause the mass to blacken, after which it burns away 

 as tinder, and, if required, the ignition is completed over the lamp. Should 

 any fear exist that some metallic bismuth has been formed, nitric acid is 

 added to the ash, and the heating repeated, so as to destroy the nitrate of 

 bismuth thus produced. From the solution the bismuth may be removed by 

 sulphuretted hydrogen. 



Ch. A. Bcehme relates an occurrence which appears to lead to the conclusion 

 that chloral hydrate may be spontaneously decomposed when kept in sealed 

 bottles. Two of these, each containing lib. of the substance alluded to, were 

 obtained from a leading drug-house at New York ; one of the bottles was 

 opened at once, and nothing special noted in its contents ; the other bottle 

 was placed in a store-room, and on being after some time opened, a dense 

 cloud of fumes was observed to issue from its mouth. These fumes had the 

 characteristic odour of chloral hydrate, but were more stifling, reddened blue 

 litmus-paper, and, on further testing, were found to consist partly of hydro- 

 chloric acid. The lumps of the hydrate near the top of the bottle had 

 crumbled to a crystalline powder freely soluble in water, somewhat in chloro- 

 form, but insoluble in sulphide of carbon and oil of turpentine. The author's 

 opinion is that the sample alluded to was pure hydrate of chloral at first, but 

 had been decomposed by standing. 



A subject of some importance in analysis has been pointed out by Mr. J. 

 Myers, who finds that sulphuretted hydrogen is often contaminated with 

 arseniuretted hydrogen. At the ordinary temperature the two gases alluded 

 to can co-exist without decomposition, which only takes place at the boiling- 

 point of mercury. The author, while experimenting, thought that the 

 arseniuretted hydrogen might be due to the presence of some arsenic in the 

 sulphuret of iron employed, but, on investigation, it turned out that the source 

 of the arsenic was in the commercial sulphuric acid used for the evolution of 

 the sulphuretted hydrogen. 



LIGHT. 



The fine purple colour of the vapour of iodine has been found by Dr. 

 Andrews, F.R.S., to arise from its transmitting freely the red and blue rays of 

 the spectrum, while it absorbs nearly the whole of the green rays. The trans- 

 mitted light passes freely through a copper-red or a cobalt-blue glass. But if 

 the iodine vapour be sufficiently dense, the whole of the red rays are absorbed, 

 and the transmitted rays are of a pure blue colour. They are now freely 

 transmitted as before by the cobalt glass, but will not pass through the red 

 glass. A solution of iodine in sulphide of carbon exhibits a similar dichroism, 

 and according to its density appears either purple or blue when white light is 



