340 The Art of Electro-plating and Gilding. 



his deposits will appear almost to enter the pores of the metal 

 deposited upon; while if his surfaces are contaminated with 

 grease, or with metallic oxide, although he may obtain a deposit 

 to all appearance most satisfactory, it will be found to consist 

 of a mere shell covering his mould, which, in some cases, may 

 be easily removed, or will even separate of its own accord. 

 Hence it becomes our first concern to know how metallic sur- 

 faces may be rendered perfectly clean, the cleansing process 

 being a preliminary operation to every case of deposition. All 

 dirt and impurity in reference to this subject, may be arranged 

 under two divisions, — first, greasy matters ; second, metallic 

 oxides ; and the means used to remove impurities of these two 

 kinds will remove almost all others. 



For the removal of grease, chemistry at once points out the 

 use of alkaline solutions. Soda, potash, or ammonia in any 

 form will answer the purpose, and convenience will generally 

 decide which should be adopted in any particular case. It is, 

 however, commonly found advantageous to use the above alka- 

 lies in the form of common commercial " soda," of pearl-ash, 

 dissolved in clean rain water, or of hartshorn. If the form of 

 the article be such as admits of rubbing up with a stiff brush, 

 it should be well brushed, with the addition of fine sand or 

 emery-powder, immediately before placing it in the plating 

 solution. In many cases, as with copies of coins, the dry 

 method — that is, with brush and sand — is not only sufficient 

 but the best that can be used; care being taken, of course, 

 to see that the brushes are free from grease, and that neither 

 hand nor fingers touch the object on the parts to be de- 

 posited upon. 



For the removal of oxides, the brush and sand or emery 

 should be used whenever the form of the object will admit of it. 

 If the object have crevices or recesses which cannot be reached 

 by a brush or other means of dry cleansing, it will be necessary 

 to have recourse to an acidified solution. Sulphuric, nitric, or 

 hydrochloric acid, diluted with water, will answer the purpose; 

 but it will be necessary to observe that, if the solution be 

 strongly acid — as, for instance, half acid and half water — the 

 object must not be immersed for more than a second or two 

 without examination ; if the solution be weak, it may remain a 

 minute or more. When it is sufficiently apparent that the sur- 

 face is cleansed from oxidised matters, it should be washed in 

 several waters successively ; a weak alkaline wash may then be 

 applied for the removal of all traces of acid, and, filially, one or 

 two more water-washings for the removal of any possible im- 

 purities that may yet remain. 



In practice, it will bo convenient in most cases to use both 

 the above methods, or a modification of either, as the judgment 



