THE OPTICAL ASSAY OF SUGARS. 



original Clerget process the concentration of the acid and of the sugar is 

 greater than it is in that due to Herzfeld, and since the levo-rotation of 

 levulose increases with concentration and with increasing strength of acid, a 

 higher value for the constant is obtained. This point is of extreme importance 

 and is one which is perhaps not uncommonly overlooked. 



Of greater importance than the concentration of the acid is the tempera- 

 ture factor ; the temperature should he observed at the moment of making a 

 reading, the water-jacketed tube referred to in the previous Chapter being used. 



Irregularities in the Clerget Process and Colour of 

 Solution after Inversion. In certain cases, especially with low grade 

 molasses, the solution becomes so dark coloured after inversion that it can only 

 be read with great error or in a state of high dilution ; this inconvenience may 

 be overcome thus. 



a. To the solution after inversion a Kttle bone charcoal is added, the 

 whole shaken and filtered ; absorption of the reducing sugars does not occur. 



I. To the solution as it cools is added a crystal of sodium sulphite ; the 

 sulphur dioxide generated decolourizes the solution. 



c. To the solution as it cools a little zinc dust is added, the decolouration 

 being now due to the nascent hydrogen evolved. 



Effect of Lead. In the presence of basic lead acetate the left handed 

 rotation of levulose decreases, the normal value being restored on neutralization. 

 Hence, as has been shown in particular by Tervooren, 30 the direct reading 

 should be taken after acidification of the filtrate after clarification with basic 

 lead acetate. Tervooren's routine for eliminating the error in the analysis of 

 molasses is 



" Dissolve 35-816 (26-048 X X f X |J) grms. molasses in 250 cc. 

 water, with the addition of 40 cc. basic lead acetate ; receive 100 cc. of the 

 filtrate in a 100-110 cc. flask; add 1 cc. of 30 per cent, acetic acid and 

 2 cc. of alumina cream, make up to 100 cc., then filter and polarize. The 

 reading multiplied by 2 is the direct reading." 



Increase in Rotation of Levulose. In the presence of hydrochloric acid the 

 gyrodynat of levulose increases; hence when levulose is initially present, a 

 positive error is introduced. Browne 24 states that this error is corrected for by 

 deducting from the percentage of sugar '36 per cent, for every 1 per cent, of 

 levulose present, when 10 c.c. of hydrochloric acid, sp. gr. 1-18, are used per 

 100 c.c. of sugar solution. 



Modifications of the Clerget Process. Various agents other 

 than hydrochloric acid have been used to effect the inversion, such as oxalic 

 acid, employed in the proportion of one part per 100 of sugar at a temperature 

 of 50C. 60C. for several hours. Yeast as an agent was first used by 

 0' Sullivan and Thomson 25 as follows : 50 c.c. of the solution under analysis 

 are raised to a temperature of 55C. ; some brewers' yeast in quantity ^ 



455 



