250 METALS. 



of tin may be made with tin-foil, in a tea-cup or test- 

 tube. 



618. Aqua-regia,) it will be remembered. 



What is the 



action of aqua- is a mixture of nitric and muriatic acids. 



regia on tin ? Jn most caseg they ^ &g before degcribedj 



in concert, to dissolve metals that neither can dissolve 

 alone. They act thus, also, upon tin, in small por- 

 tions. But if larger quantities are employed, the mix- 

 ture grows warm, and the nitric acid, as if stimulated 

 beyond restraint, attacks the metal for itself, and con- 

 verts it, as when it acts alone, into a white powder. 



619. COATING PINS. Common brass pins 



How are pins 



coated with are coated, by boiling with cream of tartar 

 tin? and tin-foil, or bits of tin. The acid of 



the tartar acts as solvent. Tin is then deposited on 

 the mere electro-positive brass, as in cases of galvanic 

 decomposition. At every point where brass, tin, and 

 the liquid are in contact, a small galvanic battery is, in 

 fact, produced. 



How is tin 620. TIN WARE. Tin is cast in va- 



plate made ? r i ous forms, for culinary and chemical uten- 

 sils. A little lead is added to give it greater tough- 

 ness. Common tin ware is made of sheet-iron, coated 

 with tin. The coating of the metal is effected by 

 dipping well cleaned sheet-iron into molten tin. 



621. CRYSTALLINE TIN. Tin has a great 



How may the " 



crystalline tendency to assume a crystalline form. 

 *tin C bele.en? The stmct ure may be observed on wash- 

 ing the surface of ordinary tin plate with 

 aqua-regia, to remove the thin coating of oxide. It 

 may be still better seen if a tin plate is heated over a 



