106 



ELECTRO-PLATING. 



and place them in this solution to within half an inch of the mouth, 

 and fill them to the same height with the solution : in these porous 

 vessels place small plates or sheets of iron or copper, and connect 

 them with the zinc terminal of a battery : in the large solution place 

 a sheet or sheets of silver connected with the copper terminal of the 

 battery. This arrangement being made at night, and the power em- 

 ployed being two of Wollaston's batteries, of five pairs of plates, the 

 zincs 7 inches square, it will be found in the morning that there will 

 be dissolved from 60 to 80 ounces of silver from the sheets. The 

 solution is now ready for use : and by observing that the articles to 

 be plated have less surface than the silver plate forming the positive 

 electrode, for the first two days, the solution will then have the pro- 

 per quantity of silver in it. We have occasionally found a little 

 silver in the porous cells ; it is therefore not advisable to throw away 

 the solution in them without first testing it for silver, which is done 

 by adding a little muriatic acid to it. 



The amateur electrotypist may, from this description, make up 

 a small quantity of solution for silvering his medals or figures ; for 

 example, a half-ounce of silver to the gallon of solution will do 

 very well : a small quantity may be prepared in little more than an 

 hour. 



Other solutions of silver may be employed, if the law stated at 

 page 91 is strictly observed. Indeed, every salt of silver has not 

 only been tried, but is either the subject of a patent, or promi- 

 nently included in it. None of them, however, with the exception 

 of two, have we found of any practical value, besides that already 

 described : these are the chloride of silver dissolved in hyposulphite 

 of soda, and the sulphite of silver dissolved in sulphite of potash, or 

 sulphite of soda. 



Hyposulphite of silver Solution. The simplest method known to 

 us for forming the hyposulphite of silver solution is this : Take one 

 pound of pure carbonate of soda well dried as described at p. 92 ; 

 mix it intimately with five ounces of flower of sulphur ; place the 

 mixture over a slow fire without flame, in a porcelain or stoneware 

 basin, which must be supported by an iron trellis, or any con- 

 venient support, to prevent it touching the red coal or flame : keep 

 the mixture constantly stirring, and maintain the heat till the sulphur 

 melts, and the mass inclines to get pasty and rough : while in this 

 state, keep stirring for about fifteen minutes, in order to bring every 

 part in contact with the air. Set the mixture to cool, after which 

 dissolve it in water : boil the solution for some time, adding sulphur; 

 then filter it, and allow it to evaporate at a slow heat : the crystals 

 formed are hyposulphite of soda. 



To prepare the silver solution, the silver is first dissolved in nitric 

 acid, and then precipitated by a solution of common salt, and washed. 



