HEATING APPARATUS FOR POLARIMETERS 
165 
AN IMPROVED HEATING APPARATUS FOR MAINTAIN- 
ING CONSTANT TEMPERATURES IN WORK WITH 
POLARIMETERS AND REFRACTOMETERS. 
J. N. PEARCE. 
In the course some work upon the effect of temperature 
upon the specific rotation of optically active substances in solu- 
tion, it was found necessary to maintain constant temperatures 
over long periods of time. The conditions demanded that the 
heating apparatus be one which is simple and convenient and 
at the same time one which permits the easy reproduction of 
any given temperature. 
Various forms of apparatus devised for this purpose are de- 
scribed in the literature. Some of these consist in principle of 
a coil for running water heated either by a Bunsen flame, or 
an electric coil. Where such methods are used in large crowded 
chemical laboratories the results obtained are unsatisfactory 
owing to fluctuations both in the gas and water pressures. Sev- 
eral modifications of this form were tried and discarded. While 
satisfactory as regards the regulation of temperature, the heat- 
ing apparatus devised by Landolt for polarimeters is never- 
theless inconvenient. 
After several attempts the apparatus sketched in the accom- 
panying diagram was perfected and the results obtained far ex- 
ceeded our expectations. 
In the figure, A is a round cylindrical vessel 25 cm. in di- 
ameter and 40 cm. in depth. Directly in the center and at the 
bottom of A is soldered the small cylinder, R, 6.2 cm. in diameter 
by 7.5 cm. in depth. V/ithin the small -cylinder rotates a motor- 
driven stirrer of propeller form. At C, slightly below the water 
level, is soldered a 9 mm. galvanized iron tube. A similar tube 
opening directly into the center of B is soldered to the bottom 
of the bath. The two open ends, D, E, are attached directly to 
the jacketed observation tube by means of short pieces of rubber 
tubing. Surrounding the bath is a layer, F, of felt or asbestos 
paper. 
