390 Scientific Intelligence. 



principles of solubility. At a given temperature there will be 

 but one saturated solution possible when both salts are present in 

 excess, provided the salts form no double salts with each other. 

 If one double salt forms, there will be two definite saturated 

 solutions, one when A and AB are both present as solids, the 

 other when AB and B are present. The single salts alone or a 

 double salt alone can exist in contact with a series of saturated 

 solutions containing A and B. It follows that when two salts, 

 either simple or double, are present in the solid state the composi- 

 tion of the solid will change as the relative proportion of the 

 two salts changes, but the composition of the saturated solution 

 will remain constant. When, however, only one salt, either 

 simple or double, is in the solid state its composition must remain 

 fixed, while the composition of the saturated solution varies 

 within certain limits. Bj^ making a series of saturated solutions 

 with a pair of salts, therefore, and determining the composition 

 of the solutions and the residues, it is possible to determine the 

 composition of every double salt that is formed. Dr. Foote has 

 applied the method in several cases with entirely satisfactory 

 results ; for instance, he has shown that five caesium mercuric 

 chlorides, and no others, exist at the temperature of the experi- 

 ments. These salts, sCsCl.HgCl,, 2CsCl.HgCI,, CsCl.HgCl,, 

 CsC1.2HgCl2 and CsCl.sHgCl, were described by Wells in this 

 Journal in 1892. The method, which is an application of the 

 Phase Rule of the late Professor Gibbs, promises to be exceed- 

 ingly serviceable in the investigation of double salts, for b}'' its 

 use every double salt, whether well-crystallized or not, can be 

 detected, while by the old method some members of a series 

 might easily be overlooked. — Aniev. Chem. Jour.^ xxx, 330, 339. 



H. L. W. 



5. Ausgeicdhlte Methoden der Analytischen Cheniie / von 

 Prof. Dr. A. Classen. Zweiter Band, 8vo, pp. xvi, 831. Braun- 

 schweig 1903 (Viewegund Sohn). — The first volume of this excel- 

 lent reference-book for practical analysts has already been noticed 

 in this Journal. The present second volume deals with the non- 

 metallic elements, and it need only be repeated here that every 

 analytical chemist should have access to this valuable work. 



H. L. w. 



6. Physical Chemistry in the Service of the Sciences; by 

 Jacobus H. van't Hoff. English version by Alexander Smith. 

 8vo, pp. 150, C'hicago 1903. (The University of Chicago Press.) 

 — This book comprises a series of nine lectures delivered in June, 

 1901 at the decennial celebration of the University of Chicago. 

 The subjects discussed, after an introductory address, are the rela- 

 tion of physical chemistry to pure chemistry, industrial chemistry, 

 physiology and geology. In view of the eminence of the author 

 it is hardly necessary to say that these lectures give an excellent 

 account of the more important achievements of physical chem- 

 istry. H. L. w. 



7. Penetrative Solar Radiations. — M. R. Blondlot believes 



