110 ELECTRO-PLATING. 



a weak battery may be used ; though when the battery is weak the 

 silver deposited is soft, but if used as strong as the solution will 

 allow, say 8 or 9 pairs, the silver will be equal in hardness to rolled 

 or hammered silver. If the battery is stronger than the solution 

 will stand, or the article very small compared to the size of the plate 

 of silver forming the positive electrode, the silver will be deposited 

 as a powder. The average cost of depositing silver in this way is 

 2d. per ounce. G-as should never be seen escaping from either pole : 

 the surface of the article should always correspond as nearly as pos- 

 sible with the surface of the positive electrode, otherwise the deposit 

 runs the risk of not being good ; it requires more care, and the 

 solution is apt to be altered in strength. 



In plating large articles (such as those plated in factories), it is 

 not always sufficient to dip them in nitric acid, wash and immerse 

 them in the solution, in order to effect a perfect adhesion of the two 

 metals. To secure this, a small portion of quicksilver is dissolved 

 in nitric acid, and a little of this solution is added to water, in suffi- 

 cient quantity to enable it to give a white silvery tint to a piece of 

 copper when dipped into it: the article then, whether made of 

 copper, brass, or German silver, is, after being dipped in the nitric 

 acid, and washed, dipped into the nitrate of mercury solution till 

 the surface is white : it is then well washed by plunging it into two 

 separate vessels containing clean water, and finally put into the 

 plating solution. This secures perfect adhesion of the metals. One 

 ounce of quicksilver thus dissolved will do for a long time, though 

 the liquor is used every day. When the mercury in this solution is 

 exhausted, it is liable to turn the article black upon being dipped 

 into it: this must be avoided, as in that case it also causes the 

 deposited metal to strip off 



Practical instruction in Plating. We need hardly add that it is 

 necessary the battery should be so arranged, that the quantity of 

 electricity generated should correspond with the surface of the 

 articles to be coated, and that the intensity should bear reference to 

 the state of the solutions ; that is to say, that the quantity should be 

 sufficient to give the required coating of metal in a given time, and 

 the intensity such as to cause the electricity to pass through the 

 solution to the articles. It is also essential, for regular working, 

 that the plates of metal forming the positive pole in the solution 

 should be of corresponding surface to the articles to be coated, and 

 face them on both sides. 



The following is the arrangement adopted in some of the large 

 plating manufactories : The vat or plating vessel measures about 

 6^ feet in length, by 33 inches in breadth, and 33 inches in depth, 

 and generally contains from 200 to 250 gallons of solution; the 

 silver plates serving as electrodes, which formerly were nailed upon 



