436 The Philippine Journal of Science i»i8 



calculation when applied to the same sample gave the following 

 results : 



Sample A. 



Per cent. 

 Insoluble matter none 



Lead dioxide (PbO») 27.02 



Combined lead monoxide (PbO) 54.52 



Free lead monoxide (PbO) 18.54 



100.08 

 Lead dioxide (Pb0 2 ) 27.02 



Combined lead monoxide (PbO) 54.52 



Red lead 81.54 



1 gram of original sample contains {g.llH ££ pIq 6 combined. 

 Combined PbO in red lead proper = 66.86 per cent. 



From Table II, 66.86 per cent combined PbO corresponds to 

 a mixture of (80 per cent Pb 3 O 4 +20 per cent Pb 4 5 ). 



81.54 x 0.80 = 65.23 per cent Pb 3 4 in original sample. 

 81.54 x 0.20 = 16.31 per cent Pb^Os in original sample. 



According to this method of calculating results, the analysis 

 of sample A would be : 



Per cent. 



Insoluble matter none 



PbO (litharge) 18.54 



Red lead j Ph '°< (m™™0 65.23 



lPb.0 



16.31 

 100.08 



When the lead content is computed from these data and 

 checked by a total lead determination, the following. results are 

 obtained : 



Per cent. 



Total Pb by direct determination 91.37 



Total Pb by direct calculation 91.21 



Difference 0.16 



By this method of calculation the total lead determination 

 serves as a check on the entire analysis and the agreement 

 between the calculated and determined total lead content of the 

 sample is very close. 



In Table III are given the data for a number of samples of 

 red lead which have been investigated in accordance with this 

 method of analysis and calculation. 



