26 DESCRIPTION OF GALVANIC BATTERIES. 



one part sulphuric acid, should be put into the pan, sufficient in 

 quantity to cover the zinc plate, which should lie in it till the surface 

 is perfectly bright. The pan is now raised on the one side, and a, 

 little mercury put into the lower part, care being taken that the 

 zinc does not touch the mercury, to prevent which is the object of 

 raising the pan on one side. A little coarse tow, tied to the end of 

 a piece of wood, is dipped into the mercury, which lifts small portions 

 of the metal mechanically, which is then rubbed with considerable 

 pressure upon both sides of the zinc plate, over which the mercury 

 flows easily: the plate is then washed by dipping it into clean water, 

 and is next made to stand upon its edge in another pan, with two 

 small pieces of wood under it, so as to allow the mercury to drain 

 from it. Instead of tow, an old scratch brush is generally used in 

 plating factories : this is a brush made of fine brass wire, tied upon 

 a piece of wood ; but we prefer tow, when carefully employed, as 

 the brass wire amalgamates with the mercury, and causes a loss of 

 that metal. After the zincs have drained for a few hours, the pro- 

 cess should be repeated, only it is not necessary to allow the metal 

 to lie in the acid in the second process previous to rubbing in the 

 mercury : after draining a few hours the second time, amalgamation 

 is completed. In the first process a plate, of a foot square, amalga- 

 mated on both sides, will retain three ounces of mercury ; but for 

 the second process, or any time after, the same size of plate will only 

 retain 1| ounces of mercury. 



The zinc in the battery, after being used, should never be allowed 

 to lie in the acid when the battery is not in use, but should be taken 

 out, and the surface carefully brushed with a hard hair brush, in 

 water, and then laid by in a safe place. The matter thus brushed 

 off, being an amalgam of zinc, is to be carefully collected and kept 

 in dilute sulphuric acid, or in the waste acid from the batteries : 

 most of the zinc will dissolve out, so that a great portion of the 

 mercury may be recovered, or by placing these brushings in a coarse 

 cloth bag, and subjecting it to pressure in a screw-press, most of the 

 mercury may be recovered. 



Economy in Amalgamation. If the battery is to be used seldom, 

 and only for a short period at a time, another method of amalgama- 

 tion may be adopted. The zinc plate, after lying in the dilute acid 

 till the surface is bright, may be rubbed over with a solution of 

 nitrate of mercury, which gives a very thin amalgamation ; but this 

 method is unsuitable if the battery is to be in use for several hours 

 together. 



When a battery is being worked daily, it will be advisable to 

 repeat the amalgamation from time to time, otherwise local action 

 will begin, and the working power of the battery be weakened, while 

 the loss in zinc will be increased. 



