RICHARDS AND BONNET. — DISSOLVED CHROMIC SULPHATE. 7 



Here the difference between the analyses of the " dialyte " and 

 residue is vastly greater than any possible analytical error, and in the 

 opposite direction from the slight one observed in the case of the violet 

 salt. The portion which diffused through the diaphragm contained much 

 more of the sulphuric group in proportion than that which remained be- 

 hind. From the analysis, the deficiency of acid in the residue seems to 

 be less than the excess of acid in the dialyte merely because less than 

 quarter of the material was allowed to pass through the diaphragm. 

 The total deficiency, on the one hand, of course exactly equalled the 

 total excess on the other. These facts agree essentially with the results 

 of van Cleef. 



In support of these data it is worthy of note that the green boiled solu- 

 tion is strongly acid to methyl orange. 



Clearly the results of dialysis, complicated as they are by the con- 

 tinual reversion of green to violet, are too involved to furnish more than 

 qualitative evidence that hydrolysis has really taken place in the green 

 solution. The qualitative evidence is nevertheless indubitable. 



Catalytic Action. 



Long suggested in 1897 that the green chromium solution probably 

 inverts cane sugar, while the violet does not. Modern hypothesis con- 

 tends, as is well known, that ionized hydrogen is the cause of this kind 

 of catalytic action ; hence the speed of the inversion might afford a meas- 

 ure of the extent to which the chromic solution has been hydrolyzed. 



The strength of color of the solutions makes the use of the polarimeter 

 impossible, hence the ingenious method used by Kahlen berg and Davis* 

 was employed for determining the extent of the inversion. This method 

 depends upon the fact that invert sugar has about twice as great a de- 

 pressing effect on the freezing point of water as the cane sugar from 

 which it is made. The catalyzer is assumed to exert a constant effect on 

 the freezing point. Thus the progress of the inversion may be followed 

 by taking successive measurements of the freezing point of the solution. 



Our sugar solution contained about 250 grams in the litre. It was 

 carefully sterilized by intermittent heating on three successive days ; 

 and the permanent apparatus for delivering measured quantities of the 

 solution was also sterilized. If suitable precautions of this kind are 

 taken, the solution will of course preserve its strength for months. A 



* Jour. Am. Chem. Soc, 21, p. 1 (1899). 



