METHODS OF ESTIMATING CARBOHYDRATES 



41 



excess of basic lead acetate, added as a clarifying agent. 

 He took the precaution of adding this reagent cautiously, 

 so that there was but little excess. Under these con- 

 ditions he found that the rotation even of the fructose was 

 not appreciably affected, whilst on the other hand a small 

 loss in total sugars followed the treatment with hydrogen 

 sulphide. Thus, apparently, Parkin's results are free from 

 any serious objection on the score that they were obtained 

 with leaded solutions. At the same time my own experi- 

 ence has been that, when dealing with sap pressed from 

 leaves and centrifuged to remove debris, it is quite im- 

 possible to avoid adding excess of the basic acetate, for the 

 whole solution becomes a yellow slimy mass. 



TABLE XIX. 

 COMPARISON OF AIR-DRIED AND FROZEN LEAVES. 



Parkin employed the tables of Brown, Morris, and Millar 

 (1897), for his reducing sugars, and, since maltose was 

 absent, inverted the sucrose with hydrochloric acid under 

 Clerget conditions namely, by heating 50 c.c. of solution 

 with 5 c.c. of concentrated hydrochloric acid for fifteen 

 minutes at a temperature rising to 68. 



