1914-15.] 
Tlie Optical Eotation of Sugars. 
27 
Prepaeation of Sugar Solutions. 
The sugar, after drying to constant weight, was again finely powdered — 
this being done in a large desiccating case provided with openings for the 
hands — weighed in a tube, and emptied into a dry 10-c.c. or 25-c.c. glass- 
stoppered fiask, and the solvent added and the whole vigorously shaken 
till solution was complete. In some cases the solution had to be filtered 
to remove particles of fibre, which caused opacity of the solution. The 
first measurements of the rotation were made as soon as solution was 
complete, the time being taken from the instant when the sugar came in 
contact with the solvent. 
^-^-Arabinose. 
The arabinose was dried at 105® till of constant weight. It was 
perfectly colourless, and melted at 151° (uncor.). 
Cryoscopic measurements gave the following data : — 
Solvent. 
Concentration per 
100 grams of solvent. 
Mol. weight 
found. 
Mol. weight calcu- 
lated, CjH^oOs- 
Water 
1-23 
148*4 
150 
2-28 
149*0 
55 
Formamide 
0-39 
153*0 
J? 
0-77 
144*7 
?? 
0-66 
158*5 
1-22 
155*7 
V 
