198 



ELECTRICAL RESISTANCE OF ACETIC ACID 



that the specific resistance increased great- 

 ly after each freezing. The greatest num- 

 ber of freezings attempted in any one case 

 was five. "With more freezings, a purer 

 sample could, no doubt, be obtained. How- 

 ever there is a limit to the purity obtainable 

 in this manner as you can't prevent the 

 absorption of moisture from the air: and 

 there is also some dissociation. It was 

 thought that the traces of water might be 

 eliminated by adding acetic anhydride 

 (Kahibaum's C. P.) to the acid. This was 

 tried but it was found that the specific con- 

 ductivity of the anhydride was greater than 

 that of the acid. Traces of HCl. were 

 afterwards found in the anhj^dride. which 

 would account for its conductivity. 



I The resistance vessel, A, (see figure 5), 



Laa^.J was blown from glass tubing of .7 cm. 



bore and mane about 12cm. long Into 

 the tube were sealed two platinum elec- 

 trodes. Oi and Oo, each of which had an area 

 of about 2 sq. cm. and a chromicsulphuric 

 acid cleaning solution was used. NaOH 

 was then used and finally alcohol to remove 

 grease etc. After washing man}' times with 

 distilled water, the vessel was dried care- 

 fully. To ensure the removal of as much moisture as possible 

 from the glass, the tube was connected to a mercury pump and 

 heated to about 160° C in an oil bath for several hours. The 

 pump was exhausted at intervals over a period of two days. 

 The "cell constant" was determined by measuring the 

 resistance of a -h X. solution of Kcl on a Kohlrausch bridge^ 

 The tube was then sealed off and suspended in a test tube 

 filled with oil, which was placed in the thermostat. On 

 account of capacity effects it is essential that the thermostat 

 be well earthed. 



F,g, 5 



' Kohlrausch, F., Physico. Chem. Measurements. 



