ANALYSIS AND COMPOSITION OF RED LEAD 



By Augustus P. West 1 



(From the Laboratory of General, Inorganic, and Physical Chemistry, 

 Bureau of Science, Manila, P. I.) 



When lead is heated to a temperature of low redness, the 

 monoxide (PbO) is obtained. When the temperature is carefully 

 regulated and kept below the melting point of the monoxide, the 

 product obtained is a yellowish powder known as massicot. If 

 the monoxide is melted during the preparation, the product is a 

 reddish solid known as litharge. The commercial monoxide of 

 lead is a yellow to reddish yellow solid, the color and specific 

 gravity of which vary with the conditions of formation. When 

 lead monoxide is heated in the air at a temperature of from about 

 300° to 550°, oxygen is gradually absorbed and a red product 

 is obtained known as minium or red lead. At temperatures 

 above 550°, red lead is decomposed to lead monoxide. 



Various methods have been proposed for estimating the purity 

 of red lead, but they are all more or less unsatisfactory. Al- 

 though red lead has been investigated extensively, the exact com- 

 position is still an unsettled question. The object of this paper 

 is to describe a method which has been found satisfactory for 

 determining the purity and composition of red lead. 



Commercial red lead is usually regarded as a mixture of 

 minium (Pb 3 4 ), uncombined lead monoxide (PbO), and small 

 amounts of impurities (such as red clay, barium sulphate, iron 

 oxide, and sand). 



Analyses of 16 samples by F. Lux 2 showed the impurities to 

 vary from 1.4 to 13.5 and the uncombined lead monoxide from 

 2.3 to 42.5 per cent. 



D. Woodman 3 in 21 analyses found the uncombined lead mon- 

 oxide to vary from 8 to 59 per cent. 



Woodman's method for determining the purity of red lead 

 consists simply in leaching out the free litharge with lead acetate 

 solution and in determining the red lead by difference. 



When minium is treated with dilute nitric acid, it decomposes 

 according to the equation 



PbaO, + 4HNO, -» PbO, + 2Pb (NO,) 2 + 2H.0 



1 Assistant professor of chemistry, University of the Philippines. 

 ' Zeitschr. f. anal. Chem. (1880), 19, 155. 

 'Journ. Am. Chem. Soc. (1897), 19, 339. 



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