25 
1914-15.] The Optical Rotation of Sugars. 
method, and the data obtained proved this to be the case. Apparently no 
such determinations of molecular weights were made by the above men- 
tioned investigators of mutarotation in pyridine and formic acid solution ; 
and, though there is no reason to suspect that the molecular weights in 
pyridine solution are abnormal, there is much reason to expect that in 
formic acid solution complicated changes take place, and that the data 
obtainable from cryoscopic or ebullioscopic measurements would give 
evidence of such changes. 
The mutarotation experiments in formamide solution gave results com- 
parable to those obtained in aqueous solution, though the rate of muta- 
rotation was slower in the former than in the latter solution. The 
mutarotations in pyridine solution as obtained by Grossmann and Bloch 
are inserted for the sake of comparison. 
EXPERIMENTAL. 
Formamide. 
The formamide used was supplied by C. A. F. Kahlbaum and was purified 
by careful fractional distillation under diminished pressure. The dehydra- 
tion by means of anhydrous sodium sulphate previous to distillation under 
diminished pressure, as recommended by Walden (Zeitsch. phys. Chem., 1903, 
xlvi, 145), was not found to offer any advantage over direct distillation. 
Formamide distils at 99-100"’ under 11 mm. pressure, using a fine capillary 
air inlet. Walden mentions the melting-point as + 2*1° and the conductivity 
*25 = 4-7 X 10“^, and our experiments confirm these numbers, our data being, 
melting-point -f-2-l° and x^^ = S'2 x 10“^ 
The cryoscopic constant used — 38'5 — was that of Bruni and Trovanelli 
(Gazz. chim., 1904, 343, 350). 
Water. 
The distilled water of the laboratory was used. 
Cryoscopic Apparatus. 
The ordinary Beckmann freezing-point apparatus was used, the 
thermometer being graduated in 0’02° and read with the help of a lens, 
so that the limit of error in reading was approximately 0'01°. To prevent 
access of moist air, dry air was bubbled through the side tube, escaping 
through the small glass tube in which the stirrer moved. 
