﻿232 Scientific Intelligence. 



experimental evidence, no less than general considerations, show 

 that the water molecules in a lower hydrate are affected by the 

 addition of more water. The higher hydrate does not contain 

 the lower one ; (6) the displacement of one of the water mole- 

 cules in the magnesian sulphates by K 2 S0 4 affords no grounds 

 for the supposition that the one displaced differed in any respect 

 from the others. The physical properties of the resulting double 

 salt afford a strong argument in favor of the displaced molecule 

 being water of crystallization only ; (7) that the specific heats of 

 hydrated salts throw no light on the nature of the different 

 water molecules; (8) that experiments with the solid hydrated 

 sulphates of the magnesian metals show that the volume of the 

 water in the lower hydrates is relatively less than in the higher 

 hydrates. But the difference is not such as would indicate any 

 difference in nature of any of the various hydrates, and certainly 

 affords no information as to the volumes of the individual water 

 molecules in any particular hydrate ; (9) that the volume of dis- 

 solved salts may show that one molecule of water in these mag- 

 nesian sulphates differs from the rest ; but the data available are 

 at present too meager to warrant any definite conclusions being 

 drawn. At any rate, whatever the difference may be, it is of 

 exactly the opposite nature to that which would be exhibited if 

 it were water of "constitution;" (10) that with the exception of 

 this last-mentioned fact, which can at present be regarded as a 

 possibility only, we have no grounds for supposing that the 

 various water molecules in a hydrated salt are not all combined 

 in a similar manner, and do not all occupy exactly the same 

 position with regard to the salt-nucleus ; that in short a hydrated 

 salt is not a symmetrical substance. At the same time it must 

 be admitted that we have no positive evidence to show that it is 

 symmetrical, and we must regard it as such provisionally only, 

 till some unquestionable evidence in favor of or against this view 

 be forthcoming. — J. Chem. Soc, xlix, 411-432, June, 1886. 



G. F. B. 



3. On the Fulminating silver of Berthollet. — Raschig has 

 studied the compound obtained by Berthollet nearly a hundred 

 years ago by the action of ammonia upon silver oxide. For the 

 preparation of the substance, a solution of silver nitrate was pre- 

 cipitated with sodium hydrate, and the silver oxide washed by 

 decantation. For each gram of silver nitrate used, there was 

 poured upon the silver oxide 2 cubic centimeters of an ammonia 

 'solution containing 25 per cent of NH 3 . The oxide of silver dis- 

 solved readily leaving only a slight turbidity. The solution thus 

 obtained was divided into several portions, each being placed in 

 a porcelain dish about 10 cm in diameter, so proportioned that no 

 dish contained the oxide from more than one gram of nitrate. 

 Each dish was covered with a watch glass and allowed to stand 

 for 16 to 20 hours. The ammonia evaporated and the fulminat- 

 ing silver was deposited, as a black crystalline mass. After 

 washing it was analyzed by digestion with very dilute sulphuric 



