472 Scientific Intelligence. 



the drops will not change in size, but if one of the solutions is 

 stronger in this respect, its drops will increase in size at the 

 expense of the other. The method then consists in finding a 

 known solution of the same vapor tension as the known one by 

 microscopic measurement of the drops. It is not necessary that 

 the solvent used should have a constant melting point or a 

 constant boiling point, hence impure solvents, such as ether satu- 

 rated with water, 90 per cent alcohol or 80 per cent acetic acid 

 can be used successfully. The solvent should not be too volatile, 

 on account of the difficulty of manipulation, and, on the other 

 hand, if the solvent is not sufficiently volatile, the experiment 

 takes too long. The details in regard to the application of the 

 method need not be given here, but it may be observed that the 

 process has been tested with a great variety of substances with 

 satisfactory results. — Jour. Chem. Soc, lxxxv, 286. h. l. w. 



3. Hub idium- Merc uric Double Salts. — Grossmann has pre- 

 pared the double salts 



2RbI • Hgl 2 , 

 Rbl • Hgl 2 , 



2RbSCN-Hg(SCN) 2 , 

 and RbSCN • HgSCN, 



and also a pyridinium-mercuric cyanide-thiocyanate, 



(C 6 H„N)SCN • Hg(CN),. 



From these results it appears that rubidium iodide forms a much 

 less extensive series of double salts with mercuric iodide than is 

 the case with caesium iodide, for with the latter five double salts 

 are known. The double thiocyanates under consideration corre- 

 spond exactly to the caesium-mercuric salts described by Wells 

 and Bristol, except that one of the latter, 2CsSCN ■ Hg(SCN) 2 ■ 

 H 2 0, contains water ; hence there is no evidence in this case of a 

 more extensive series of salts with caesium than with rubidium. 

 The pyridine compound is an example of the combination of mer- 

 curic cyanide with many kinds of salts. — Berichte, xxxvii, 1258. 



h. l. w. 



4. Zirconium Tetra-iodide. — By acting upon metallic zir- 

 conium or upon zirconium carbide with hydrogen iodide at 

 elevated temperatures, Stahler and Denk have obtained the 

 tetra-iodide Zrl 4 in the form of a sublimate, consisting of a red- 

 dish brown, crystalline powder which fumes strongly in the air 

 and reacts violently with water and acids. This substance is 

 entirely different from the product, supposed to be this compound, 

 obtained by Dennis and Spencer several years ago, which con- 

 sisted of white crystals that were not decomposed by water or 

 dilute acids. It appears, from the close analogy known to exist 

 between the compounds of titanium and zirconium, that the com- 

 position of the white compound was incorrectly determined. — 

 Berichte, xxxvii, 1135. h. l. w. 



