404 



Mr. T. Gray on the Electrolysis 



having been taken out, the box was brought up close to the 

 back of the magnetometer. It was then found to have several 

 magnetic poles, but particularly a north pole on one side, and 

 a south pole on the other side of the position where the gal- 

 vanometer-needle was suspended. This polarity, although 

 sensible enough to the test here made, was so small that it 

 could not be detected with certainty by a magnetometer 

 placed in the Earth's field. The frame of the galvanometer- 

 coil when tested in a similar manner showed signs just per- 

 ceptible of magnetism, but so small as to produce no sensible 

 effect on the indications of the instrument. 



The brass case was then replaced by a glass cell, and two 

 other measurements taken with deflections of about 40° and 

 60° respectively, the results obtained being '0011183 and 

 •0011182; but on continuing the experiment the indications 

 of the galvanometer were found to have become uncertain, 

 due apparently to some defect in the insulation, which has 

 not yet been investigated. The results so far as they go seem 

 to confirm the value given by Kohlrausch and Lord Rayleigh 

 as closely as could be expected, but no great value can be put 

 upon them. In subsequent work the value '001118 was 

 assumed to be sufficiently accurate for our purpose. 



Katio of Silveb to Copper. — A number of experiments 

 were made for the purpose of determining the ratio of the 

 electro-chemical equivalents of silver and copper. These 

 involved the determination of the effect of density of solution, 

 the effect of repeated use of the same solution, and the effect 

 of current-density. 



Effect of Density. — The effect of changing the density of 

 the solution was only gone into sufficiently to show that no 

 important error is likely to arise from this cause. The re- 

 sults of two experiments are given in Table II. They show 

 a slightly smaller deposit from weak than from strong solu- 

 tions; but the absolute difference of weight, only a fifth of a 

 milligramme, if the somewhat doubtful result from the weakest 

 solution be omitted, is too small to found any conclusion upon. 



Table II. 





Comparative weight of 



Current density in amperes 





deposit in grammes. 



per sq. cm. 





1. 



2. 





1-20 



•2352 



•3519 



0-02 



1-16 



•2350 



•3418 



0-02 



112 



•2351 



•3517 



0-02 



1-08 



•2350 



•3518 



0-02 



105 



•2347 



•3512 (?) 



0-02 



