374 



APPLIED SCIENCE 



FIG. 184. A Buckle. 



419. White Lead Bases of Paint. The bodies in a paint 

 that are responsible for covering the material painted are 

 called " bases." The " bases" form 

 the mass of the solids contained in 

 paints. The substances added to 

 give colors are known as pigments. 

 Sometimes the bases play the part of 

 a pigment, as in the case of white lead, 

 zinc white, iron oxide, and red lead. 

 The principal base is usually white lead, a basic carbonate of 

 lead, which is produced, by the so-called Dutch process, as 

 a white amorphous powder. It is dense and has a good body. 

 A number of distinct operations go to make up the Dutch 

 process. (See Figs. 184-187.) 



(a) The lead which has been extracted from the ore and refined, 

 comes to the white lead factory in the form of pigs. There it is 

 immediately melted and recast into perforated metal disks, called 

 "buckles." These buckles are about 5 in. in diameter and 34 i n - 

 thick. 



(b) The buckles are placed in earthenware corroding pots, which 

 somewhat resemble flower-pots as to shape. 



These pots are so constructed, however, as to 

 permit the disks to rest upon a ledge some two 

 inches from the bottom. Into this space acetic 

 acid is poured before the buckles are inserted. 



(c) The pots, containing the acetic acid sur- 

 mounted by the disks, are then piled in a stack- 

 house. The stacks consist of alternate layers of 

 20 in. thick tan-bark and corroding pots. Each 

 stack is about 22 ft. long, 20 ft. wide, and 30 

 ft. high. 



(d) The tan-bark slowly decomposes, ferments, and creates a 

 heat strong enough to warm the acetic acid until vapor is given off. 



(e) The acetic acid vapor steams up through the perforations in 



FIG. 185. 



