in the Constmction of Voltaic Batteries. 151 



yet it was very faint. The result was different when sulphate 

 of copper was used. The electrolyzation commenced almost 

 the instant that the trough was filled, and continued in the 

 same way as when zinc was employed ; indeed I could observe 

 very little difference as to energy of action, and to the time 

 that it continued, with this exception, that in general there 

 was rather less gas evolved in the volta-electrometer. That 

 evolved by the action of 1250 of the sulphate in the zinc 

 trough being 180, that afforded by the same quantity in the 

 iron trough was 173, or about yVth part less. When the sul- 

 phate was mixed with nitre and with sea salt, there was an 

 increase in power, similar to that when using them in the zinc 

 trough. When therefore blue vitriol is to be used in voltaic 

 arrangements, iron may be employed instead of zinc, with very 

 nearly the same electrolytic power. It has been already men- 

 tioned that when the blue vitriol is mixed with nitre, but more 

 particularly with sea salt, the expense is only about one half 

 of that incurred by the use of oil of vitriol. If iron be em- 

 ployed in the construction of the trough, the expense must of 

 course be still further reduced, sheet iron being only about 

 half the price of sheet zinc. Though in many cases it may 

 be thought advisable to use sheet iron, there is no necessity 

 for always having recourse to it. I have found that cast iron 

 answers nearly as well ; and when the troughs are to be long 

 and much in action, it may perhaps be more ceconomical to 

 use it, as there is always expense incurred by the repeated 

 soldering of new iron plates to the copper ones ; besides cast- 

 iron is cheaper than the other. 



Before using the trough when constructed of iron, it is al- 

 ways necessary to wash the iron plates with diluted sulphuric 

 acid, which may be done before they are soldered to the cop- 

 per, or after it, by placing them in the trough filled with the 

 acid, and leaving them there for a few minutes. 



Considering the cheapness of the materials used and the 

 comparatively little waste of electrolytic power, I conceive that 

 the trough as thus recommended may be employed advan- 

 tageously for many purposes of decomposition. Supposing 

 the iron trough to be used with sulphate of copper, metallic 

 copper and green vitriol are the products in the trough, 

 both of which may be turned to account; so that if by the 

 electrolytic action of a powerful battery, a valuable ingredient 

 could be obtained from the electrolyte, the decomposition 

 might in this way be advantageously accomplished. 



There is one advantage attending the use of metallic solu- 

 tions. The adhesion of the precipitated copper does not seem 

 to impede much the action in the trough, and consequently 



