PREPARATION OF ARTICLES FOR PLATING. 109 



washed from the ley, and dipped into dilute nitric acid, which 

 removes any oxide that may be formed upon the surface : they are 

 afterwards brushed over with a hard brush and sand, of which a 

 kind obtained from the Isle of Wight, and known as silver-sand is 

 best. The alkaline ley should be in a caustic state, which is easily 

 effected by boiling the carbonated alkali with slaked lime, until, on 

 the addition of a little acid to a small drop of the solution, no effer- 

 vescence occurs. The lime is then allowed to settle, and the clear 

 liquor is fit for use. The ley should have about half-a-pound of 

 soda ash, or pearl-ash, to the gallon of water. The nitric acid, into 

 which the article is dipped, may be diluted to such an extent that 

 it will merely act upon the metal. Any old acid will do for this 

 purpose. In large factories the acid used for dipping before plating 

 is generally afterwards employed for the above purpose of cleaning. 

 The article being thoroughly cleaned and dried, has a copper wire 

 attached to it, either by twisting it round the article or putting it 

 through any open part of it, to maintain it in suspension. It is then 

 dipped into nitric acid as quickly as possible, and washed through 

 water, and then immersed in the silver solution, suspending it by 

 the wire which crosses the mouth of the vessel from the zinc of the 

 battery. The nitric acid generally used and found best for dipping 

 is of specific gravity 1'518, and contains 10 per cent, sulphuric acid, 

 and is got at about 3d. per Ib. The article is instantaneously coated 

 with silver, and ought to be taken out after a few seconds and well 

 brushed. On a large scale, brushes of brass wire attached to a lath 

 are used for this purpose ; but a hard hair brush with a little fine 

 sand will do for small work. This brushing is used in case any 

 particle of foreign matter may be still on the surface. It is then 

 replaced in the solution, and in the course of a few hours a coating 

 of the thickness of tissue-paper is deposited on it, having the beauti- 

 ful matted appearance of dead silver. If it is desired to preserve 

 the surface in this condition, the object must be taken out, care 

 being taken not to touch it by the hand, and immersed in boiling dis- 

 tilled water for a few minutes. On being withdrawn, sufficient heat 

 has been imparted to the metal to dry it instantly. If it is a medal 

 it ought to be put in an air-tight frame immediately, or if a figure, it 

 may be at once placed under a glass shade, as a very few days' ex- 

 posure to the air tarnishes it, by the formation of a sulphuret of 

 silver, and that more especially in a room where there is fire or gas. 

 If the article is not wanted to have a dead surface, it is brushed with 

 a wire brush and old ale or beer, but the amateur may use a hard 

 brush and whiting. It may be afterwards burnished according to 

 the usual method of burnishing, by rubbing the surface with con- 

 siderable pressure with polished steel or the mineral termed blood- 

 stone. We may remark, that in depositing silver from the solution, 



