632 SCIENCE PROGRESS 



in too well-defined stages and the formula of the hydrate is 

 then, probably, correctly represented by the usual formula. 

 On the other hand, hydrates such as the above require at least 

 the double formula for correct representation, and in some 

 cases even more multiple formulae may be required. Thus, 

 dihydrated cadmium acetate loses up to one and three-quarters 

 molecules of water easily in a steam oven, whilst the last 

 quarter requires a further and more elevated stage of heating, 

 indicating that the hydrate contains probably eight molecules 

 of water and ought to be represented by the formula 

 (CdAc 2 ) 4 .8H 2 0. 



With hydrates or solvates where the number of solvent 

 molecules exceeds two, the problem immediately becomes 

 much more complex. The classic case of pentahydrated 

 copper sulphate will serve as an example. Over calcium 

 chloride at 21-23 two molecules of water are lost, and the 

 pale sky-blue trihydrate remains. This hydrate gives up a 

 further two molecules of water at 6o°, whilst the last molecule 

 is lost only on heating at 206 . If the pentahydrate is heated 

 at 206— 207 it loses four molecules within half an hour, whereas 

 the final molecule is lost only very slowly and in two half- 

 molecule stages, the latter of which is the most difficult of all 

 to carry out. From such considerations as these Guareschi 

 suggests that the monohydrate has a constitution represented 

 by the double formula : 



O OH OH 



Cu SO O SO Cu 



\>/ \ / 



Preparative. — In view of the importance, at the present 

 time, of the conversion, on the industrial scale, of calcium 

 nitrate into ammonium nitrate for explosives, the recent work 

 of Le Chatelier and Bogitch {Compt. Rend. 191 5, 161, 475) 

 on the subject is of considerable value. In practice the 

 synthetic Scandinavian calcium nitrate, nitrolim, is converted 

 into ammonium nitrate by double decomposition with gas 

 works ammonium sulphate. The difficulty of the process is 

 the nitration of the pasty precipitate of calcium sulphate which 

 is obtained. 



These investigators find that this difficulty can be overcome 



