Conductivity of Organic Acids in Ethyl Alcohol. 131 



Since the percentage temperature coefficients of conductivity for 

 substances dissolved in alcohol, as well as the coefficient of expansion 

 of the alcohol itself, are so large, it is necessary to regulate the tempera- 

 ture as closely as possible. This was done by the combination of a 

 specially devised gas-regulator and thermo-regulator. These have 

 already been described in a paper by Davis and Hughes. 1 



The constant-temperature baths were of the improved form designed 

 by Davis, 2 of this laboratory. These baths are of about 60 liters 

 capacity and are made of copper. Heat is applied to a heavy iron 

 pipe outside the bath, and water is kept circulating through this pipe 

 by means of propellers. Only a small portion of the water in the ther- 

 mostat comes into immediate contact with the heated surface, and this 

 portion is subsequently mixed with the main body of water, thereby 

 securing much more even distribution of temperature. In these baths 

 ordinarily the temperature does not vary more than 0.02, which is 

 sufficiently constant for our purpose. With greater precautions as to 

 insulation against changes in temperature, and with further modifi- 

 cation of the thermo-regulator, the variation can be decreased to a few 

 thousandths of a degree. 



A ^-horsepower direct-current motor served as the source of power 

 for the stirrers, the power being transmitted by belt drives. The motor 

 proved to be a great improvement over the hot-air engines formerly 

 used. 



The thermometers were of the differential Beckman type, and were 

 carefully compared with a standard Reichsanstalt thermometer, which 

 had been calibrated also at the United States Bureau of Standards. 



The resistance-box which was used throughout this entire investi- 

 gation had also been calibrated at the Bureau of Standards. A very 

 fine Kohlrausch slide-wire bridge was employed, by means of which it 

 was possible to read distances on the slide-wire corresponding to tenths 

 of a millimeter (the total length of the wire was 5 meters) . 



Flasks, pipettes, and burettes for measuring purposes were in all 

 cases carefully calibrated. 



PROCEDURE. 



The solutions of the organic acids in alcohol were made up in 200 c.c. 

 Jena measuring flasks calibrated for 25. The quantity of dried and 

 purified acid necessary to make a solution of the required normality 

 was weighed out on a watch-glass, and was washed off through a funnel 

 into one of the measuring flasks. The flask was shaken until all the 

 acid had dissolved; it was then filled to the neck with alcohol and sus- 

 pended in the 25 bath. When temperature equilibrium was reached 

 it was filled to the mark. In the meantime a conductivity cell was 

 thoroughly washed with pure alcohol and dried with filtered dry air. 



x Zeit. phys. Chem., 85, 519 (1913). "Carnegie Inst. Wash. Pub. No. 210, 121 (1915). 



