98 
POPULAR SCIENCE REVIEW. 
carbon disulphide, alcohol, and ether. Hydrochloric acid dissolves it. By- 
heating with nitric acid it is decomposed. It absorbs dry ammonia gas, 
with formation of a black non- crystalline solid body possessed of an ex- 
tremely irritating smell. On exposure to the air, it absorbs moisture, and 
becomes of sulphur-yellow colour. Upon treatment with water it is decom- 
posed, the products of the action being a white amorphous oxybromide and 
free hydrobromic acid. The oxybromide is insoluble in a solution of tar- 
taric acid, and is decomposed on subjection to a long-continued process of 
washing with water, with formation of hydrobromic acid and bismuth oxide 
("Br/'Og + xAq). — “ Chemical News,” Oct. 23rd. 
How to produce Photographic Proofs on Wood. — u Les Mondes ” of Sept. 
24th, gives the following mode as that of M. F. C. Boche : The block of 
wood is first covered with a layer of gelatin (0*39 grin, to 31 grms. of water) 
by means of a soft brush. When this coating is dry it is covered, in the 
dark, with a solution prepared of — (1) Red prussiate of potash, 7-80 grms. j 
water, 62-20 grms. (2) Ammonio-citrate of iron, 9-10 grms. in 62-20 grms. 
water. These solutions are mixed and filtered, and the mixture is kept in 
the dark. When the layer is dry it is exposed under a negative for ten to 
twelve minutes, and washed with a soft sponge, when a blue image appears. 
If thus prepared the coating does not shell off under the graver. 
The natural Formation of Nitrous and Nitric Acid , and Peroxide of 
Hydrogen. — M. L. Carius states that [“ Chemical News,” Nov. 20th] oxides 
of nitrogen may conceivably be formed from free nitrogen by electric dis- 
charges in the air during the oxidation of other bodies in the air ; oxidation 
of nitrogen by means of ozone, and formation of nitrite of ammonia by the 
evaporation of water in the air. The author finds that the two last-men- 
tioned phenomena are not attended with the production of nitrous or nitric 
acids. These acids may also be supposed to be formed by the oxidation of 
ammonia, whether caused by electric discharges, by the presence of alkaline 
bodies, or by ozone. Experiment showed that the acids in question are 
actually formed in all these cases. 
Alteration of Coal by Fxposure to moist Air. — M. Varrenstrass finds that 
the loss of weight due to slow oxidation, and to the escape of gases rich in 
carbon, may amount to one-third of the original weight. The calorific 
power sustains in this case a loss of 47 per cent. In closed store-houses the 
loss of weight was only 25 per cent., and that of heating-power 10 per cent. 
Bituminous coals undergo the most rapid alteration. 
The Colour of Chloride of Copper. — Mr. W r , N. Hartley lately [Dec. 3rd] 
read a note on this subject before the Chemical Society. He finds that the 
crystals of cupric chloride, CuCl 2 , 20H 2 , which are generally described as 
green, are really of a pale blue tint when rendered quite free from adhering 
moisture by exposure in vacuo over sulphuric acid. The green colour of the 
crystals, as ordinarily seen, he considers to be due to their being moistened 
with a film of the deep green solution of the salt. When examined by the 
dichroiscope, the light through the principal axis shows one image of an 
azure blue, and the other of an emerald green. 
The Way in which Coal is Formed. — u Les Mondes,” of Sept. 24th, 
states that M. Hirschwald, on visiting a gallery in the Clausthal mines, 
abandoned for 300 to 350 years, found some wood which had been left there. 
