An improved form of the thermoelectric osmometer developed by one of the authors has been used to study solutions of p-aminobenzoic acid, citric acid, sodium citrate, sodium salicylate, sodium benzoate, morphine hydrochloride, and papaverine hydrochloride alone and in combination with caffeine. T h e measured colligative
EXPERIMENTAL
The circuit and technique previously described (7-9) were not changed except that the regulated power supply (Leeds and Northrup part No. 099012) was installed in place of the battery and calibrating circuit of the Speedomax recorder. The slide wire of the recorder was connected to this power source through two 400-ohm resistors which served as end coils. A 100-ohm resistor was connected across the regulated power supply. The extemporaneous arrangement of 200-ohm precision resistors increased the sensitivity of the recorder from 10 mv. full scale to approximately 1 mv. full scale. Because of the fact that the recorder is used as a nu1 instrument and calibrated against the resistance box, this temporary arrangement was used throughout the course of the work. I t is planned to install the recommended range card for future work.
Attempts to stabilize the temperature regulation and otherwise to improve the stability and reproducibility of the instrument continued throughout the course of the measurements. Manual adjustment and empirical uniformity of method had to be resorted to in the early phases. The following improvements are significant: (a) a 4-L. Dewar flask was substituted for the original 1-L. flask used ___