608 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



selection of lead alloys for the manufacture of toys, statues, and 

 household utensils mentioned earlier. 



PROPERTIES AND USES OF LEAD COMPOUNDS. 



Certain members of the oxide group of chemical compounds are 

 so unstable that a small amount of heat will cause them to separate 

 into their constituent parts, freeing oxygen. Lead oxides belong to 

 this group, and in the form principally of red lead, litharge, and 

 lead peroxide, respectively, they are used in the manufacture of 

 glass, pottery, and porcelain; in the manufacture of storage batteries, 

 rubber, matches, and in the refining of petroleum. 



Ked lead is a chemical compound of two parts of lead monoxide 

 (litharge) and one part lead peroxide. It is a brilliant scarlet red 

 in color and is obtained in a number of grades, each grade having 

 some particular use. The grade used as a paint pigment has the 

 property of opacity or hiding power, and finds its most extensive 

 use as a preserving paint for metals subject to atmospheric influ- 

 ences. The several other grades of red lead are used in the manu- 

 facture of glass where it is melted with the silica and other raw 

 materials composing glass, so that its oxygen can assist in burning 

 up the impurities in the glass ; in the manufacture of varnish, where 

 it is boiled with linseed oil in the making of varnish to promote 

 the drying qualilties ; in the manufacture of storage batteries, where 

 the red lead is made into a paste with the addition of diluted sul- 

 phuric acid and is filled into the gratings or " grids " (made of 

 metallic lead) and allowed to dry. After the paste becomes hard, the 

 " grids " are placed in sulphuric acid and charged by electric cur- 

 rents, making the positive and negative plates composing the " work- 

 ings " of a storage battery. 



Litharge is a chemical compound of lead and oxygen (lead mon- 

 oxide) containing approximately 93 per cent of lead and 7 per cent 

 of oxygen. It is a buff-colored substance produced both in granular 

 and flake form. Like red lead, there are a number of grades of 

 litharge, the uses to which the different grades are put giving rise 

 to the names by which they are known commercially : Thus, glass- 

 makers' litharge, color-makers' litharge, rubber-makers' litharge, 

 varnish-makers' litharge, enamelers' litharge, potters' litharge, and 

 accumulator litharge. 



Glassmakers', varnish-makers', and accumulator litharges are used 

 in the same way as red lead and described earlier. Rubber-makers' 

 litharge is used as an accelerator and controller in the vulcanization 

 of rubber. In any considerable quantity litharge can not be em- 

 ployed for light-colored rubber, for it tends to blacken the product. 

 Potters' litharge is used for making a glaze on pottery, although 



