No. V.] 



APPENDIX. 



169 



as effectual as silver, and may be sometimes employed with advantage. 

 With this metal all that is required is to rub a little nitro-muriate of 

 platinum over it, and an immediate deposit f the black powder takes 

 place. Palladium and iridium are found nearly as effectual as platinum 

 to coat other metals with, and the platinized silver of commerce usually 

 possesses a considerable quantity of this latter metal. Within the last 

 few months an idea has prevailed in the minds of some, that wire-gauze 

 might be used with advantage ; but it is difficult to conceive where the 

 benefit would lie, for the cost of the material would be greater, the surface 

 for the same weight of metal would be less, and neither space nor power 

 gained by its adoption. 



" The liquid generally adopted to excite this battery is a mixture of 

 one part by measure of sulphuric acid, and seven of water, which will be 

 found amply strong for all purposes. When we desire greater intensity, 

 we can obtain it by the addition of a few drops of nitric acid ; but if too 

 much be used, it might attack the silver. When, however, platinized 

 platiua is employed, the nitric acid may be used with impunity. The 

 electro-metallurgist will frequently find it advisable to use dilute sulphuric 



Fro. 8. Smee's Battery, compound six cells. 



acid, only containing from ^ to the y 1 ^ of the pure acid, and adding some 

 acid when the first is exhausted ; taking care, however, that the quantity 

 of acid never exceeds ^ of the original water, for any excess above that 

 quantity will be useless, as the liquid will then become saturated with the 

 sulphate of zinc. The zinc, acid, and water being severally required to 

 excite the battery, it is possible to regulate them that they should all be 

 exhausted at once, so that the zinc should neutralize the acid, and the 

 resulting sulphate of zinc exactly saturate the water. This, however, may 

 be very interesting in principle, but practically it would be impossible to 

 act with such precision ; yet we must never forget . this fact whenever we 

 charge our batteries. 



"Numerous inquiries have been made as to what arrangement is 

 best suited for this battery; but this must depend upon the purpose 

 for which it is employed. For the student's laboratory the porcelain 

 trough of many cells appears to be best adapted ; and it is some- 

 times so constructed, that any number of cells can be employed, 

 independently of the others, as they may be required. The silver being 

 the most expensive metal, the zinc should completely surround it, so that 

 the whole of the silver may be brought into action. Where a battery is 

 required to continue in action for a very long time, as for days or even 

 weeks, a larger vessel, to contain more dilute acid, must be used : for 

 electro-metallurgical purposes it has been hitherto found most economical 



