212 Mr. Napier on the Decomposition of 



trode is an exact equivalent of another element or salt radical 

 liberated at the opposite electrode. But the results of expe- 

 rience in the deposition of metals from the above-named salts 

 have induced the electro-metallurgist to follow another law 

 somewhat at variance with that laid down by electro-chemists, 

 and which enables him to strengthen or weaken his solution 

 of metal at pleasure. Indeed there is no law which appears 

 to him more definite than that, if a large positive and small 

 negative electrode be used, there will be more dissolved from 

 the former than is deposited upon the latter ; and on the con- 

 trary, if a large negative and small positive electrode be used, 

 more will be deposited upon the negative than is dissolved 

 from the positive. 



Being aware of the decided manner in which electro-che- 

 mists have laid down the law of the decomposition of electro- 

 lytes in definite proportions, I at first looked upon the results 

 of practical experience with doubt, and in order to put it to 

 the test, and to ascertain whether the discrepancy was acci- 

 dental or not, I adopted the following practice : — the positive 

 electrode was carefully weighed every morning, previous to 

 immersing it in the gilding or plating solution, and again when ' 

 taken out in the evening, and the loss compared with the 

 amount deposited, an account of which was accurately taken. 

 This practice was continued for upwards of nine months, 

 varying at times, as^ far as practicable, the relative sizes of the 

 two electrodes and the condition of the solutions, and during 

 this period there were only five trials where the loss from the 

 positive was exactly the amount of the gain on the negative. 

 In many cases the difference did not exceed 3 per cent., but 

 the average difference was 25 per cent., and occasionally 

 as high as 50 per cent., varying in a great measure with the 

 condition of the solution and the relative sizes of the elec- 

 trodes. 



During these operations two questions suggested themselves 

 as of importance ; namely, Is this discrepancy of equivalent 

 electrolyzation confined to the double cyanides of the metals ? 

 and second, Does the amount of electricity, as indicated by 

 the oxidation of the zinc in the battery, correspond with the 

 amount of metal deposited upon the negative electrode, or the 

 quantity dissolved from the positive? 



I had observed, while making some experiments upon the 

 relative endosmose of different substances, that if sulphate of 

 copper be used in one division of a decomposition cell in 

 which the negative electrode is placed, the other division being 

 charged with water acidulated with hydrochloric acid, and 



