THE OPTICAL ASSAY OF SUGARS. 



The Effect of Concentration on the Rotation of Sugars. 



The rotation of cane sugar is but little affected by dilution ; there is, however r 

 a sensible rise in the specific rotation with dilution. 



The results of Schmitz 12 (which are those most often quoted) and of 

 Nasini and Yillavecchia 13 are in close agreement. If p is the percentage of 

 sugar, and c the concentration in grms. per 100 cc., then, according to 



Schmitz, 



p 5 _ 65 ; [] V) == 66-510 -f -004508^ - -00028052^ 2 



c 2-5 to 28 ; [*] ^? = 66-639 '0208200 + -00034603/? 2 

 and approximately, for purposes of calculation, 



o 2-5 to 28 ; [a] 2? = 66-541 -0084150. 

 Nasini and Villavecchia found 



p 3 to 65 ; [a] 20 66-438 + 010312;? -00035449p 2 . 



In very dilute solutions the results of investigators are contradictory. 

 Tollens 14 found quite irregular values, Pribram 15 found a decrease in falling 

 from^? =. 3-659 to -222, whilst Nasini and Yillavecchia found an increase in 

 falling from^ = 1-253 to -824. 



The specific rotation of dextrose increases with concentration, and is thus 

 expressed by Tollens 16 for the anhydrous body 



[a] 20 52-50 + -018796^ -f -0005168^ 2 . 



The rotation of levulose also decreases with dilution. Honig and Jesser 17 

 give the formula for c =. 60 to 95 per cent. 



[a] 20 = -113-96 + -2580, 

 c being the percentage of water in the solution. This reduces to 



[a] 2 =-(88-16 + -258^). 

 Ost found the effect of dilution to be expressed by the formula 



[a] 20 = (91 -90 + -llty) for values of p 1 to 30 per cent. 



The Effect of Temperature on the Rotation of Sugars. 



The effect of temperature, having a very considerable bearing on the valuation 

 of sugars, has been much studied, and very discordant results have been 

 recorded. A very complete bibliography of the question is given by Wiech- 

 mann. 18 With very few exceptions it is now generally accepted that the 

 rotation of cane sugar decreases with rise in temperature. "Watts and 

 Tempany 19 in a series of very careful experiments found this relation to hold 



451 



