26 
Proceedings of the Eoyal Society of Edinburgh. [Sess. 
The Polarimeter. 
The polarimeter was a Landolt-Lippich triple-field instrument, graduated 
in 0*01°, supplied by Schmidt & Haensch. A sodium flame produced by a 
Meker burner heating fused sodium chloride contained in a circular platinum 
gutter was the source of light. In the first experiments unj acketed tubes were 
used and the atmospheric temperature of the dark chamber kept as constant 
as possible. For comparison the rotations at a series of different tempera- 
tures were made, using a tube enclosed in an asbestos-covered box filled with 
water, which could be heated or cooled as required. The tubes and other 
vessels with which the solutions came in contact had been washed repeatedly 
with distilled water before use to remove alkali from the surface of the glass. 
In later experiments a jacketed 2-dcm. tube provided with a thermo- 
meter immersed in the solution was used. 
The Sugars. 
The sugars used in the following experiments were obtained from 
C. A. F. Kahlbaum. Further purification of such forms as were obtain- 
able in sufficient quantities was effected by crystallisation from aqueous 
or aqueous-alcoholic solutions. The measurement of the specific rotation 
of these optically active forms is practically the only method of testing 
their purity. In such cases as that of lactose, where well-defined crystals 
of each modification are obtainable, the specific-gravity determination 
affords valuable confirmation. The melting-points of sugars are so in- 
definite as to be of little value, generally speaking. 
Some difficulty was at first experienced in dehydrating sugars owing 
to their decomposition on long-continued heating at 105° or even lower. 
Eventually a drying apparatus arranged in the following manner was 
found to give good results. The finely divided sugar was placed in a 
copper-foil boat about 5 in. long by J in. deep and J in. broad, and the boat 
inserted into a tube B, which is sealed on to a drying tube A, filled with 
phosphorus pentoxide and having an air inlet regulated by a screw clip. 
The other end of B is provided with a rubber stopper, through which passes 
the end of a second drying tube C, which leads to a mercury pump by 
means of which a pressure of from 1 to 2 mm. could be maintained for 
hours. As a rule the tube B was kept at ordinary room temperature for 
one or two hours, and then gradually heated by means of a steam jacket to 
near 100° until constant weight w^as attained. In this manner most of the 
adherent moisture and some hydrate water were expelled at room temperature 
and the remainder at the higher temperature without decomposition. 
