Art. XI. -On the Conductivlf^/ of o Solution of Copper 

 Sulphate. 



(With Plates XV and XVI.) 



By W. HuEY Steele, M.A. 



[Read August 11, 1892.] 



The following observations were made with the intention 

 of examining, under various conditions, the conductivity of 

 a salt solution, which is of some impo)'tance at present, 

 owing to the attention being paid to solutions now by 

 Ostwald, van't Hoft, and others. I chose copper sulphate 

 (CuSO^+S HjO) to work with, as that was the most con- 

 venient. It is plentiful and easily purified, and cojjper is a 

 convenient metal to use for making the electrodes. 



All the methods of measuring electrolyte resistance by the 

 ordinary Wheatstone bridge and galvanometer are more or 

 less unsatisfactory, the only satisfactory method being that 

 suggested by Kohlrausch, namely^ of using rapidly alternat- 

 ing currents and a telephone, instead of steady currents and 

 a galvanometer. The alternate current may be produced by 

 a small dynamo, but much more conveniently by an 

 induction coil maintained by a few cells. A small coil 

 is preferable to a large one, as the statical charge on the 

 electrodes, especially it they be small, is liable to introduce 

 a sei'ious error, besides which is the annoyance of receiving 

 shocks on touching exposed ]mrts of the circuit, if one 

 works with such high E.M.F.'s as ai'e produced in a large 

 coil. The coil I used, when maintained by fou^- freshly 

 charged Grove cells, gave a spark of rather more than a 

 centimetre, but I generally used a much weaker primaiy 

 current. A slide wire bridge is generally recommended, but 1 

 found a resistance box more sensitive and more convenient. 

 The greatest sensitiveness I ever obtained was about 1 in 

 1500, that being with a resistance of 1500 ohms. The dis- 

 tribution of resistances which is most advantageous in the 

 arms of the ordinary Wheatstone bridge is by no means the 

 best in Kohlrausch's ari-aiiuement. In the former, it is 



