296 SCIENCE PROGRESS. 



and the colour of the supernatant liquid is then noted. 

 Two solutions which are just coloured after this treatment 

 have the same molecular concentration, and hence if the 

 molecular weight of one of the dissolved substances is 

 known that of the other can be calculated. The method is 

 rapid, but cannot be used for acids and bases. In carrying- 

 out the method of De Vries, Schreber (96) finds that the 

 peduncle of the dandelion affords good material, and accord- 

 ing to Hamburger (97) by the method of De Vries the same 

 results are obtained for the osmotic pressure of solutions of 

 albumen as by the methods depending on red blood corpuscles 

 or depression of the freezing-point. 



Vapozir pressure and boiling-point. — Besides the work 

 of van Laar, already referred to (94), that of Ewan (93) 

 contains a theoretical deduction of the vapour-pressure 

 formula of a strong solution. Ewan shows that the vapour 

 pressures of sulphuric acid solutions calculated by his 

 expression from the freezing-point and heat of dilution, 

 accord with the facts. 



A modification of Beckmann's boiling-point apparatus 

 for determining molecular weights has been described by 

 Linebarger (98). This and the numerous other forms of 

 apparatus which have been proposed, together with the 

 various improvements in the accessories of the boiling-point 

 apparatus, are fully discussed by Beckmann in a recent paper 

 (99), in which he describes what he regards as the most 

 suitable type. Gernhardt (100) has proposed to replace the 

 platinum wire fused through the base of the boiling-point 

 flask by a less costly piece of red Jena glass. 



From the boiling-point of alcoholic solutions, Mtiller 

 (101) finds that ferric chloride has the formula Fe Cl 3 . In 

 ethereal solution the molecular weight diminished with the 

 dilution from 200 to 151, the theoretical value for Fe Cl 3 is 

 162-5. 



Kruss and Thiele ( 102) from the boiling-point of solutions 

 in ether, benzene, chloroform and carbon bisulphide, and 

 from the freezing-point of solutions in benzene and acetic 

 acid, conclude that in these solvents iodine has the formula 

 I 2 . The difference in the colours of the solutions is, there- 



