1914-15.] 
The Optical Kotation of Sugars. 
41 
a-LACTOSE. 
This sugar was recrystallised twice from aqueous solution. Some 
difficulty was experienced in obtaining it in the anhydrous state, but this 
was overcome by means of the drying apparatus mentioned above. The 
temperature was ultimately raised to 130° before constant weight was 
obtained. 
The cryoscopic measurement of ct-lactose in aqueous solution was not 
repeated, having been done previously with great accuracy (Loomis, Zeitsch. 
physikal. Ghem., 1901, xxxvii, 407). The slow rate of solution of lactose in 
formamide, owing to the formation of gummy masses, vitiated the results 
of some experiments. The following figures are typical of an experiment 
in which solution took place rapidly : — 
Concentration per 
100 grams solvent. 
Mol. weight 
found. 
Mol. weight calcu- 
lated for Cj 2 ll 22 f^ll- 
1*783 
326*8 
342 
The specific rotations as observed in water and in formamide solutions 
are given below (c/. figs. 13 and 14). Grossmann and Bloch state that 
lactose is only soluble in pyridine to the extent of about one per cent., and 
that they were unable to obtain exact readings, but found [aj^ed initial 
— 4-20*52°, and constant =4-31*5°; a reversal of the direction of tlie 
mutarotations in water and in formamide. The small initial value is 
probably due to incomplete solution of the lactose. 
[Table. 
