112 ELECTRO-PLATING. 



side the house, and the connecting rods are brought from them into 

 the vats, so as to preserve the workmen from the injury arising from 

 inhaling the hydrogen gas which is given off by the zincs, as it often 

 contains arsenic, and hence is highly injurious to health ; but, where- 

 ever the batteries are placed, they should not be exposed to cold, as 

 their operation is much affected by the temperature. 



In the early days of electro-plating the batteries used were round. 

 They consisted of a copper cylindrical vessel, about 20 inches deep, 

 and 5 inches diameter, filled with dilute sulphuric acid. A piece of 

 wood, was placed at the bottom of this vessel, and a cylinder of zinc, 

 the same depth as the copper vessel and about 3 inches diameter, 

 was placed inside the copper vessel. A wooden ring, floating on the 

 surface of the acid, prevented the zinc and copper touching a 

 binding screw was attached to each and formed a battery of a single 

 pair. Six batteries of this size were connected with such a vat as is 

 described above. The test of strength employed to determine 

 whether the working power was sufficient, was that, when connected 

 with an electro-magnet, it should support a 7 Ib. weight. We be- 

 lieve that some platers and gilders use still such batteries, and that, 

 when the solutions and apparatus are all in good condition, they do 

 well. They are, however, far from being so economical as the bat- 

 tery with square plates shown above. Some electro-metallurgists 

 use large and deep stoneware vessels, in which are placed the zinc 

 and copper the plates having several square feet of surface. We 

 have already shown, when treating of batteries, that very large 

 plates are not consistent with economy. 



To ascertain the amount of metal deposited, it is only necessary 

 to weigh the articles carefully before .and after plating. But 

 between the first weighing and the immersion of the articles in 

 the plating solution there is the dipping into nitric acid to be ac- 

 counted for: this, on an average, will cause a loss of about one 

 pennyweight upon an article of the size of a foot square ; thus, if a 

 waiter of a foot square, made of copper or German silver, show, 

 when coated, a difference in weight of 19 pennyweights, the silver 

 laid on must be estimated at an ounce, or 20 pennyweights. When 

 the article is a "replate," i. e., an old plated article that has become 

 bare of silver in parts, the allowance or reduction for the dipping in 

 the acid is only to include the portions left bare, for the silvered 

 parts are not acted upon by it. One of the practical difficulties 

 which the inexperienced will occasionally meet with when a " re- 

 plate " is dipped in the nitric acid, is, that a galvanic action is pro- 

 duced between the silver and the copper portions, which causes 

 a black line round the edge of the silver: this ought immediately to 

 be rubbed off, but even with rapid and careful rubbing there is 

 great danger that the coating will loosen and blister at those parts ; 



