Dilute Solutions of Hydrochloric Acid. 59 



its contents is now weighed, and the concentration of the solution 

 can thus be calculated when that of the stock solution is known. 

 Three such stock solutions were prepared ; the strongest ('2154 

 normal) was estimated by precipitation as silver chloride, and the 

 other two were obtained by diluting this with weighed quantities 

 of water. The water used had an average conductivity of about 

 10~^ reciprocal ohms at 18° C. 



The cell was immersed in a tank of water, which was well 

 stirred and maintained at a temperature of 18° C. by means of 

 a toluene regulator. 



The method of carrying out an experiment was as follows. 

 The solution was made up in the pipette M, of which the delivery- 

 tube was ground to fit the upper end of the vertical tube P. 

 A current of air, purified from ammonia and carbon dioxide, was 

 then slowly drawn through the cell, being introduced through the 

 tube K and led out at G and H. The liquid was then run in 

 from the pipette up to a mark on the tube at P, the volume of 

 solution used being thus the same in all the experiments. The 

 pressure over K was now increased, so that the liquid covered the 

 electrodes B, G, and the resistance at each end measured several 

 times by means of a commutator and galvanometer. 



The liquid was now brought back to its original position, and 

 a current passed through the solution from Aj to A^, usually for 

 about an hour. The current was obtained from a battery of about 

 40 storage cells, and was measured by balancing the e.m.f. across 

 the ends of a resistance included in the circuit (varying from 

 2000 to 30000 ohms according to the strength of the solution) 

 against the e.m.f. of a Clark cell. The current was maintained 

 at a constant value by adjusting the applied e.m.f. by means of 

 a potential-divider. 



After switching off the current, the pressure at K was again 

 increased, and the separated portions of the solution stirred by 

 means of the electrodes A. The resistance was then measured at 

 each end, as at the beginning of the experiment. 



Let R, R be the measured resistances at the cathode before 

 and after the passage of the current, k, k' the corresponding con- 

 ductivities of the acid, and v) the conductivity of the water. We 

 then have 



k' + w _R 

 J+^~R" 



1 ^T n Bk 8R 



and therefore , = -^=^ , 



k + w R 



where SR = R' - R, 8k = k - k'. 



