vni, a, 6 West: Analysis and Composition of Red Lead 



431 



red lead in the sample is not to be directly computed from the 

 percentage of lead dioxide. 



In 1850, Mulder 5 showed that in red lead the percentage of 

 oxygen above that required in lead monoxide varies from 1.16 

 to 2.67 per cent. Several samples of red lead agreed in com- 

 position with the formula Pb 4 5 . In Table I is given the oxygen 

 content of various oxides of lead. 



Table I. — Oxygen content of various lead oxides. 



Compound. 



Oxygen. 



Oxygen 

 greater 

 than oxy- 

 gen con- 

 tent of 

 PbO. 



PbO 



Per cent. 



7.12 



8.81 



9.35 



10.39 



Per cent. 



PD406 .' 



1.69 

 2.23 

 3.27 



Pb304 



Pb20s - 





According to Mulder's results, it appears that some samples 

 of red lead consist of mixtures of different oxides of lead. 



In 1851, Mulder's results were confirmed by Jacquelain, 6 who 

 examined a number of samples of red lead and noticed that the 

 oxygen content varied considerably. 



In 1889, Lowe 7 pointed out that both the oxides Pb 3 4 and 

 Pb 4 5 may be present in red lead, but that the commercial arti- 

 cle containing free extractable PbO probably consists of a 

 mixture of Pb 4 5 and PbO. 



Whether one or both of the oxides Pb 3 4 and Pb 4 B are present 

 in a sample of pure red lead, can be determined in the following 

 manner: By leaching with a solution of lead nitrate, any free 

 PbO can be eliminated, leaving only pure red lead. Now minium 

 when heated above 500° gives lead monoxide and a loss of 2.34 

 per cent of oxygen. If the compound Pb 4 5 behave in a similar 

 manner, it would be decomposed according to the equation Pb 4 5 

 -> 4 PbO -f and the oxygen loss would be 1.76 per cent. Know- 

 ing the oxygen loss of a mixture of the oxides Pb 3 4 and Pb 4 5 , 

 we can calculate the amount of each present in the mixture. 

 However, since the figures representing the loss of oxygen are 

 rather small, the experimental error involved in determining 



'Journ. f. prakt. Chem. (1850), 50, 438. 



'Ibid. (1851), 53, 161. 



1 Dingier' s polytech. Journ. (1889), 271, 472. 



