3 04 SCIENCE PROGRESS. 



isoamyl oxide. At Jahn's suggestion Schonrock made ex- 

 periments which seemed to show that this result was due 

 to chemical action between the gas and the isoamyl oxide. 

 Perkin finds, however, that there is no appreciable action 

 even after three days, and he also finds that the rotation 

 in alcohol is almost the same as in isoamyl oxide. These 

 results clearly illustrate the difference in the behaviour of 

 water and indifferent solvents. 



As regards the colour of solutions, Sabatier (136) has 

 determined the absorption spectra of solutions of cupric 

 bromide, and Ostwald (137) has interpreted his results in 

 terms of the dissociation hypothesis. On the other hand, 

 Kastle (138) concludes that no known theory can explain 

 the colour phenomena of salt solutions, and he attributes 

 them to chemical processes. Magnanini (139) also finds 

 that the salts of violuric acid do not agree with the dissocia- 

 tion hypothesis. He gives evidence which shows that 

 the ions of the acid are colourless, whereas solutions 

 of its alkaline salts are not colourless, but red. Again, on 

 adding nitre to the solutions, the colour is not affected, 

 although nitre should diminish the dissociation, and thus 

 the colour of the solutions. 



Buckingham (140) has tried to show that the fluores- 

 cence of salts may be correlated with their ionisation, 

 and Bandrowski (141) considers that the light which is 

 sometimes emitted during crystallisation is an electrical 

 phenomenon associated with the ions, but in neither case is 

 the evidence convincing. 



Density and ot her properties. — The effect of temperature 

 and pressure on the density of a solution, according to 

 several papers (142) by Tamman, can be expressed by 

 saying that the thermodynamic surface of a solution ap- 

 proximately coincides with that of the solvent if the zero 

 of pressure in the case of the solution be taken to be not one 

 atmosphere, as in the case of the solvent, but one atmo- 

 sphere plus a definite pressure. 



Kohlrausch and Hallwachs (143) have described an 

 accurate method for determining the density of very dilute 

 solutions, and obtained a series of values for saline solutions. 



