LEAD — M1TMAN. 613 



that on which the Old Dutch Process is based. In each instance the 

 lead is first changed to acetate of lead and then converted into 

 hydrated carbonate of lead. 



The Carter process takes about 12 days to convert the lead into 

 white lead. The rapidity of the process is due to the finely divided 

 state of the metallic lead with which it starts. By this method 

 granulated lead resembling gunpowder is sprayed with acetic acid 

 in a great revolving wooden drum. As in the Old Dutch Process, 

 the acid immediately attacks the lead, forming acetate of lead. 

 Purified coal gas which contains carbonic acid gas is then introduced 

 and changes the acetate of lead to white lead. 



In the Matheson process the metallic lead is first " feathered," or 

 made to resemble a sponge in structure, by running molten lead into 

 water. It is then dissolved in acetic acid, and by contact with car- 

 bonic acid gas, precipitated in the form of a white powder which 

 is hydrated carbonate of lead or white lead. 



MANUFACTURE OP LITHARGE AND RED LEAD. 



By far the greater proportion of litharge is made by calcining or 

 roasting pig lead in. specially constructed furnaces, called reverbera- 

 tory furnaces, so named because the heat is reverberated or thrown 

 down from an arched roof upon the material being treated. The 

 hearth of the furnace is about 10 feet square and fireplaces are at 

 opposite sides from which the flame is directed to the arch of the 

 hearth. The arch is 2^ to 3 feet above the hearth. The method of 

 the manufacture of litharge is substantially as follows: About 1| to 

 2 tons of pig lead are placed in the furnace. At 620° F. the lead begins 

 to melt but there is not much oxidation until the temperature is 

 raised considerably, and it is often as high as 1,600° before oxidation 

 is complete. While the lead is molten, it is constantly stirred or 

 " rabbled " with iron-handled rakes mechanically operated so that all 

 parts of the lead are exposed to the oxidizing action of the air. 

 Gradually the molten mass becomes granular, and with continued 

 heat all of the lead is converted into oxide or litharge. The process 

 requires from 24 to 36 hours, and in that time, with the tempera- 

 ture at from 1,100° to 1,600° F., the lead takes up all the oxygen that 

 it will hold in its present condition. If the heat has been sufficiently 

 iutense to render the oxide pasty, it will, upon cooling, break down 

 into small reddish-yellow flakes, known as flake litharge. The 

 litharge as drawn from the furnace is then taken to a grinding 

 mill where it is first pulverized, then floated on water so that any 

 particles of metallic lead may settle out, and finally dried and 

 packed. It is during the pulverization that the litharge assumes the 

 buff color. 



101257—22 10 



