Ionizing Power of Solvents. 



3 



remarkable result obtained for mixtures of formic acid and 

 water should be confirmed. This has now incidentally been 

 done in the course of a careful series of experiments by 

 Dr. Vladimir Novak, whose paper follows this one. 



As the object of the investigation was merely to test the 

 general behaviour of the mixtures, no great accuracy was 

 sought, and a simple form of apparatus was sufficient. Kohl- 

 rausclr's telephone method was adopted for the conductivity 

 measurements, a straight-wire bridge being arranged in the 

 usual manner. Instead, however, of using a battery and 

 induction-coil as the source of current, the town supply, 

 alternating about 100 times a second, was sent through the 

 longer coil of a simple transformer, the shorter coil of thick 

 wire being connected with the bridge. This arrangement is 

 in constant use at the Cavendish Laboratory, and gives 

 excellent results, the sensitiveness being both greater and 

 more uniform than with the usual arrangement. 



Two cells were used to contain the solutions, one giving a 

 much higher resistance than the other. Their forms are 

 represented in figs. 1 and 2. When in use each cell was 



Fig. 1. 



Fig. 2. 



C^ 



$u 



immersed in a water-bath, the temperature of which could be 

 easily adjusted. 



The process of the experiments was as follows : — The acid 

 sold as pure was placed in cell No. 2 and weighed. Its resist- 

 ance at a known temperature was then measured in the w T ater- 

 bath. Successive quantities of water were then added, first 

 from a pipette which bad been adjusted to deliver half a 



B 2 



