On the Law oj Electro-chemical Equivalents. 211 



It is with this view that 1 have undertaken the following expe- 

 riments, bj' means of which I have compared the quantities of 

 copper, hj'drogen, and silver separated by the current. I have 

 also tried some experiments upon lead, but they did not lead to 

 a satisfactory result. 



I. Comparison of the quantities of copper and hydrogen sepa- 

 rated by the same current. — The comparison of the quantities of 

 copper and hydrogen separated by electrolysis has been effected 

 by means of a somewhat complicated apparatus, which it would 

 be difficult to describe completely without the aid of a figure. I 

 shall therefore confine myself to indicating briefly the mode in 

 which I have operated. 



An electrical current traversed simultaneously a solution of 

 sulphate of copper, and some acidulated water. The copper 

 deposited on a platinum wire was weighed directly. The hy- 

 drogen was determined by combustion, as in an organic analysis. 



In preparing the sulphate of copper, in its electrolysis and the 

 weighing of the deposit, I operated exactly in the same manner as 

 in the researches upon the salts of copper previously referred to. 

 Considerable difficulty is met with in the exact determination of 

 the quantities of water decomposed by the pile. In fact it is to 

 be feared that a portion of the gas set free combines afresh. 

 The circumstances which may be in favour of this recombination 

 are, — 1, the mixture of the hydrogen and oxygen in the presence 

 of the platinum wires, especially if a part of the oxygen is in the 

 state of ozone ; 2, the contact of the hydrogen dissolved in the 

 water with oxygen in the nascent state; 3, the formation of 

 binoxide of hydrogen, that is to say, of a very oxidizing body 

 which may burn the hydrogen. These causes of error are avoided 

 principally by separating the gases from the moment of their 

 formation, and raising the temperature of the electrolyte. The 

 best mode of separating the gases appeared to me to consist in 

 plunging the electrodes in two separate test-tubes, united by a 

 siphon filled with acidulated water. They were kept at a tem- 

 perature of ]40° to 158° F. The hydrogen disengaged from 

 one of these test-tubes passed first through a series of desiccating 

 apparatus, and then traversed a combustion-tube. The water 

 was absorbed in weighed tubes. A current of atmospheric 

 air which traversed the apparatus at the same time, served to 

 draw the whole of the hydrogen into the combustion-tube at the 

 conclusion of the experiment, and to prevent the detonations 

 which would inevitably have been produced if the proportion of 

 hydrogen had been consideral^e. 



I made a certain number of ])reliminary experiments to deter- 

 mine the strength of the pile which it would be necessary to em- 

 ploy, and to ascertain the limit of exactitude in the observations; 



