LEAD MITMAN. 607 



hardness and toughness are so increased that all three requisites are 

 met. Again, variations in the proportions of metals forming an alloy 

 cause a change in the properties of the latter. Thus a certain mix- 

 ture of lead and antimony produces type metal while another com- 

 bination of these two metals with arsenic is required for lead shot. 



Until recently there were recognized only two alloys of lead, i. e., 

 alloys in which lead forms the greater portion of the mixture. 

 These were type metal and shot metal. The scarcity of tin (ex- 

 tensively used, and the chief metal of many bearing metal alloys, 

 such as Babbitt) during the war caused an intensive search to be 

 made for a bearing metal requiring no tin. The result was the find- 

 ing of an alloy fulfilling this requirement and composed of 99 per 

 cent lead and small amounts of barium and calcium. Tests made 

 upon this new metal by the Bureau of Standards showed that it 

 possessed all the requisites of a good bearing metal, namely, hard- 

 ness, compressive strength, low friction, heat resistance, and low cost. 

 Its melting point is about the same as that of lead, and it can be 

 readily rolled, drawn, extruded, and used in die cast form. 



Again, the plasticity, hardness, and weight of lead have caused its 

 use in certain alloys extensively employed for the manufacture of 

 organ pipes ; the keys of flutes, clarinets, and similar parts of other 

 musical instruments. 



4. FUSIBILITY OB MELTING POINT. 



Much of the importance of lead is due to its low fusibility or ease 

 of melting. The principal uses for lead based on this property are 

 shown in plate 6. In addition to these uses, lead forms an im- 

 portant ingredient of certain metals used in the manufacture of 

 toys, statuary, and household utensils. 



5. RESISTANCE TO CORBOSION. 



Most metals are attacked by acids, acid vapors, and salts, but 

 the amount of corrosion varies considerably. On lead it is less 

 violent than on many metals, and accordingly lead is used in the form 

 of sheet and pipe for the water connections of dwellings and office 

 buildings (especially for carrying off waste), in chemical plants, and 

 for covering electric cables. 



6. CASTING QUALITY. 



When molten lead is poured into a mold and allowed to solidify 

 it is observed that it takes a very sharp impression of the mold, 

 filling the most narrow as well as the widest crevices. For this 

 reason, mainly, all printing type contains a large percentage of lead, 

 other ingredients being added to harden it, toughen it, and increase 

 its fusibility. This property is likewise influential, in part, in the 



