590 ANNUAL EECORD OF SCIENCE AND INDUSTRY. 



part of salt of tin in water, by first sj^rinkling them thinly 

 with zinc filings, and then pouring the warmed tin solution 

 over them. The latter liquid must not be too strong, and it 

 is therefore best to add the concentrated solution of tin salt 

 and cream of tartar, gradually, drop by drop, so that the tin 

 coating may form slowly. This should appear of a beautiful 

 bluish, dead white. The articles must remain an hour lono:- 

 er in the liquid, and then be rinsed and dried (the smaller 

 in sawdust). Brass, copper, or German -silver articles, pol- 

 ished, or freshly cleansed in an acid bath, and also copper- 

 coated iron and zinc ones, may be silvered as follows : Dis- 

 solve 210 grains of silver in 390 grains of nitric acid, and 1800 

 grains of cyanide of potassium in one quart of water ; mix 

 the solutions, and add 420 grains of powdered chalk. Smooth 

 objects may be silvered by being rubbed Avith this, with the 

 addition of some Spanish white. Chains and small articles 

 may be placed in an unglazed earthen vessel and strewed 

 with Avhiting, which is then moistened, and the objects are 

 shaken about with it, and then as much of the silvering liquid 

 gradually added as may be necessary, until the coating seems 

 uniform and sufiiciently heavy. Brass which is to present 

 both dead and polished surfi^ces must first be deadened as 

 follows: Saturate one quart of nitric acid with zinc, mix sul- 

 phuric acid with hydrochloric until effervescence ceases, and 

 add one third as much of nitric acid to the mixture, and 

 then as much of the zinc solution as may be necessary to pro- 

 duce a deadening liquid of the desired quality. The articles, 

 after being dipped in this, are to be rinsed, and then bright- 

 ened by covering with snuff" and dipping in pure nitric acid, 

 withdrawing quickly, and immediately rinsing in plenty of 

 water, to the last portions of which it is well to add a solu- 

 tion of cream of tartar; they are then dried with linen or 

 sawdust. The polished parts must afterward be burnished 

 with blood-stone. To impart the dark gray color, and form 

 the so-called oxide, the portions to remain uncolored are first 

 protected with a coating of wax, and the parts to be col- 

 ored then penciled with sulphide of ammonium. Moderate 

 warming hastens the coloring. A bi-onze tint may also be 

 imparted to other metals in this way. The finest effect is 

 produced Avith gold ; and silvered articles may be first gild- 

 ed for this purpose, by immersing them in a bath of one hun- 



