D. CHEMISTRY AND METALLURGY. 59 



cific gravity as before, are added. The process of deposi- 

 tion with cobalt is the same as with nickel. 3- A, August 

 12,112. 



RAPID METHOD OF TINNING. 



A valuable recipe for tinning copper, brass, and iron in the 

 coftl, and without complicated apparatus, has recently been 

 published by Prof. Stolba, of Prague. A prerequisite is that 

 the article to be tinned be perfectly free from oxide or grease 

 of any kind, it being necessary that the surface be cleaned in 

 the most careful manner, although it is immaterial whether 

 this be done by mechanical or chemical means, so that the 

 desired object be effected. 



The substances used in the process are, first, powdered zinc, 

 which may be the ordinary zinc dust, called sometimes zinc 

 gray, but that w T hich is prepared expressly for the purpose 

 will be best. For this it is only necessary to melt some pure 

 zinc, and pour it into a previously warmed iron mortar. As 

 soon as it has become hardened it can be readily pulverized, 

 and should then be freed from its coarser grains by sifting. 

 The proper fineness is that of ordinary writing-sand. 



The next ingredient is a five to ten per cent, solution of the 

 salt of tin (simple chloride of tin), to which is to be added as 

 much powdered cream of tartar as can be taken up on the 

 point of a knife. Next is required a piece of sponge, or a pad 

 of some kind. The process of tinning is extremely simple. 

 The pad is first to be dipped in the solution of salt of tin, and 

 applied to the object to be tinned, so as to moisten it thor- 

 oughly. A small quantity of the zinc powder having been 

 spread out on a glass plate, a portion of this powder is then 

 to be taken up by the pad, and quickly and firmly rubbed 

 upon the article in hand. The tinning makes its appearance 

 almost immediately, and, in order that the surface may be 

 coated uniformly, it is only necessary to dip the pad alter- 

 nately into the solution of tin (which is to be kept in a little 

 dish) and into the zinc powder, and then to apply it. After 

 the operation is completed, which, for small objects, requires 

 only one or two minutes, the article is to be washed off in 

 water, and then cleaned with Tripoli, or polishing powder. 

 The effect of this application upon polished brass or copper is 

 extremely beautiful, the surface resembling silver, and keep- 



