442 APPLIED SCIENCE 



forms by hammering and then brazing (a form of soldering) 

 the plate into the desired shape, while the sheet-metal worker 

 makes a form by developing it from the sheet. 



510. Common Sheet Metals. Certain metals and al- 

 loys, such as brass, copper, lead, tin, zinc, tinned iron (tin- 

 plate), aluminum, and thin sheet iron, possess strength, 

 durability, lightness, and a clean, smooth surface. Most of 

 these metals, particularly copper and tin, possess the prop- 

 erty of malleability in a marked degree and can, as a result, 

 be hammered into various shapes without being fractured. 

 Sheet metals are made by passing metal bars through heavy 

 rollers until the desired thickness is obtained. 



Copper, the most useful of metals next to iron, is found in 

 all parts of the world, but principally in the states of Montana, 

 Arizona, and Michigan. It occurs in both the free and the 

 combined forms. The combined compounds are the oxide 

 (Cu 2 O) and the sulphide (Cu 2 S). Copper is not affected 

 by water or by oxygen at any temperature, which accounts 

 for its being found frequently in the free state. 



511. Smelting of Copper. There are two methods of 

 obtaining copper by smelting and by electrolysis. It is de- 

 sirable to mix different ores so that they will be in proper 

 condition for smelting, as one.often acts as a flux to the other. 

 The whole mass is roasted (heated to a high temperature) 

 for twelve hours in the furnace, from which it is raked out 

 in a black and pulverized condition. The next process is 

 smelting,, during which the slag or earthy part of the ore 

 rises to the surface, and is cleared off, after which the metal 

 is run into pits filled with water. This causes it to become 

 granulated. These two processes are repeated twice, and 



