304 APPENDIX. [No. XXII. 



deprived of its copper becomes so light that it rapidly rises to the top. 

 For all rapid deposition we seek to form, our new salt at the top of the 

 apparatus, that it may descend to the place where it is required, and 

 the light fluid may rise to mix with the denser portion. Practically, the 

 vertical trough is suitable for the purposes of the Bank; but however 

 important may be the requirements of this corporation, the laws of nature 

 are paramount, and will not vary to suit its convenience. 



Up to the present time the best standard salt for the reduction of 

 copper by electro-metallurgy, is the sulphate, and, with the occasional 

 exception of the nitrate, is invariably employed. We always have a neutral 

 trough containing a simple solution, three parts saturated. For general 

 purposes we use a saturated solution diluted with dilute sulphuric acid of 

 battery strength, to the extent of from one-half to one-third of the bulk. 

 We are careful to use recrystallized sulphate of copper, distilled sulphuric 

 acid, and distilled water, as all impurities are hurtful. For our positive 

 pole of copper it is very desirable to get good metal, and probably the 

 sheathing of the innumerable Russian vessels we intend to capture will 

 best serve our purpose, as the Russian copper is proverbially pure and free 

 from tin. 



If we regard the precipitating trough, we can but regard it as a very 

 curious and wonderful chemical laboratory, in which two processes are 

 being conducted at the same time, and in precisely equivalent proportions. 

 In it we have the best of all chemical factories for the production of 

 sulphate of copper by the combination of the plate of copper with the acid 

 of the salt, and in it we may perceive the most perfect of all foundries 

 wherein the metal is cast upon the mould atom by atom, with a skill which 

 rather shows the perfection of nature than the deficiencies of the opera- 

 tions of man. 



As a general rule we employ a single battery with one trough. Where 

 we desire rapid action, we employ a compound battery of two cells in 

 series, but this entails a double cost of battery power. In a great many 

 cases, where time is of no object, we employ a compound trough with a 

 single battery that is to say, we arrange two troughs in series with 

 one battery a contrivance whereby we use our battery power twice over, 

 and obtain two equivalents of copper, one in each trough, and consequently 

 at half the cost. This form of apparatus is no trouble to manage. We 

 have placed it in one of the iron safes for which the Bank is so famous, 

 and wires are carried through the wall to supply the electric power. Here, 

 unseen, and without labour or attention, the process goes on by night and 

 by day, on Sundays and holidays ; and when the deposit has acquired suffi- 

 cient thickness, the mould is taken out and the deposit removed. 



The deposited metal is of excellent quality, and a part of one of the 

 Britannias, when carefully weighed, was found to have a specific gravity of 

 8*85. To ascertain the ductibility of the metal, I sent one of the scraps 

 to Messrs. Home and Thornthwaite, and one pound of metal was found to 

 be capable of being drawn into three and a half miles of wire. 



The authorities of the Bank are justly jealous of fire, and therefore we 

 have not been able to keep our rooms or solutions at an elevated tempera- 

 ture, which is very desirable for many purposes. It is far better that we 

 should be put to inconvenience, and our processes retarded, than that one 

 single document should be jeopardized by our operations. 



