44 8 SCIENCE PROGRESS 



become substituted by other specific basic, acidic, or neutral 

 radicles. The extended researches of Ephraim and his co- 

 workers at present being carried out on the nature of subsidiary 

 valencies, may be expected to advance our knowledge on this 

 important subject. With regard to water itself further data 

 on its polymerised state has been published by Oddo (Gazzetta, 

 1915, 45, i. 319). Below 32 C. water vapour appears to be 

 ionically dissociated, at 32 the vapour density indicates the 

 mono-molecular formula, whilst above this temperature associa- 

 tion sets in, and at 270 , over 40 per cent, is in the dimolecular 

 form, H 4 2 . 



Preparative. — Zinc has lately been definitely added to the 

 list of metals forming peroxides. The new peroxide is obtained 

 by adding hydrogen peroxide to ammoniacal zinc nitrate at 

 — 5°C, and stirring the white precipitated solid with con- 

 centrated hydrogen peroxide solution. Some valuable pre- 

 parative work has been carried out by Sander (Zeit. angew. 

 Chem. 191 5, 28, 273) on polythionates. Tetrathionates hitherto 

 have never been prepared in a state of purity, and Sander has 

 been able to show that the presence of thiosulphates is a prime 

 factor in their decomposition. If, then, the tetrathionate as 

 soon as it is formed can be removed from the presence of the 

 parent thiosulphate, a pure product ought to be obtained. 

 This has now been accomplished by adding the thiosulphate 

 solution to a cooled alcoholic solution of iodine. The tetra- 

 thionate being insoluble in the alcoholic solution, is precipitated 

 out as soon as it is formed, and is obtained in a pure state. 



A new allotropic modification of lead is, according to Heller 

 (Zeit. Phys. Chem. 191 5, 89, 761), obtained by leaving pure 

 lead immersed for several days in a solution of lead acetate 

 acidified with nitric acid. The metal becomes so brittle as 

 to be capable of being powdered, and the modification is desig- 

 nated " grey lead." In the light of Cohen's extended researches 

 on metallic allotropes, this discovery is not surprising, and 

 in fact we must now look upon absence of allotropic modifica- 

 tions in a metal as something quite abnormal. Not only so, 

 but ordinary samples of a metal probably contain varying 

 proportions of different allotropes, a contingency, as Cohen 

 points out, which is highly significant as to the value of the 

 hitherto determined physical constants of metals. 





