vm, a. 6 West: Analysis and Composition of Red Lead 435 



lead monoxide, the amount of each of the oxides Pb 3 4 and Pb 4 0, 

 which compose the total red lead present in the sample is ascer- 

 tained by reference to Table II. 



d. Total lead. — This determination serves simply as a check 

 on the other determinations. 



Treat a 0.2-gram sample with 30 cubic centimeters of 10 per 

 cent nitric acid, boil until all red lead is completely changed to 

 the black dioxide, cool, and add 20 cubic centimeters of sulphuric 

 acid (1 part H 2 S0 4 to 5 parts H,0). Boil a few minutes. The 

 soluble lead nitrate is changed to lead sulphate. Now add 2 

 cubic centimeters of concentrated hydrochloric acid, and the lead 

 peroxide is changed to lead chloride. 



Evaporate to white fumes, cool, add 10 cubic centimeters of 

 water, and again evaporate to fumes. The lead chloride is con- 

 verted to lead sulphate. The lead is now determined as sulphate 

 as in the determination of free plus combined lead monoxide. 

 In the presence of insoluble matter more accurate results are, of 

 course, obtained by dissolving the lead sulphate in ammonium 

 acetate and reprecipitating. 



As red lead is only very slightly hygroscopic, moisture de- 

 terminations are seldom necessary. Occasionally, adulterated, 

 artificially colored samples are encountered. In such cases, 

 the adulteration is best detected by leaching with suitable 

 solvents. 10 



In the case of rapid work, when only approximately accurate 

 results are desired, it is not necessary to make a complete anal- 

 ysis. In the absence of insoluble matter, the free lead monoxide 

 may be determined by leaching with lead nitrate solution. One 

 hundred per cent— per cent free PbO=per cent red lead. In 

 the presence of insoluble matter 



100 per cent— (per cent free PbO+per cent insoluble matter) 

 =per cent red lead. 



This method of analysis gives very satisfactory results when 

 applied to high-grade samples which contain only red lead, free 

 litharge, and no insoluble matter. 



As previously pointed out, the analysis of red lead sample A 

 gave unsatisfactory results when the percentage of red lead was 

 calculated from the Pb0 2 content. My method of analysis and 



" Technical methods of testing miscellaneous supplies. BuU. U. S. Dept. 

 Agr., Bur. Chem. (1908), No. 109, 20. 



