On definite Proportions. 7 



5.) The experiment was repeated with 8 grammes of 

 lead, which afforded 10-32 of carbonate and 8*8 of yellow 

 oxide of lead ; so that 100 parts of lead had again taken up 

 7y of oxygen. 



Bucholz obtained from 300 grains of lead, which were 

 dissolved in nitric acid, and precipitated by carbonated 

 alkali, 320 grains of yellow oxide of lead ; besides 4y grains 

 of carbonated lead, which remained on the filler. This last 

 is taken by Bucholz, as equivalent to * grains of the yellow 

 oxide: this however is an error; the carbonate of lead 

 loses ^ of its weight, not -i- only, by ignition ; for 10 

 grammes of pure carbonate of lead, dried in a strong heat, 

 afforded me, in three different experiments, 8'33 gr. of yel- 

 low oxide, so that we must allow only 3| grains for the 

 4|, and the lead in Bucholz's experiment cannot have taken 

 up more than 7*92 per cent, of oxygen. 



From these experiments I think myself authorised to 

 conclude, that those are the most accurate which give the 

 proportion of oxy2;en from 7*75 to 7'8 for 100 of lead. 

 Consequently the yellow oxide or protoxide of lead consists 

 of Lead 92-764 or 100-0 



Oxygen 7'236 7-8 



100000 107-8 



B. Red Oxide of Lead. Red Lead. 



Red lead, as it occurs in commerce, I have found con- 

 laminated with si'.ipbate and subniuriate of lead, oxide of 

 copper, and silica : so that little dependence can be placed 

 on its analysis. Ii also contains much of the yellow oxide, 

 v.hich gives it a biighier colour than properly belongs to 

 lead in this stage of oxidation. 



In order to get rid of the yellow oxide, I digested some 

 levigated red lead with weak distilled vinegar, at a tempera- 

 ture of 68^, as long as the vinegar continued to saturate 

 itself: by these means the yellow oxide was dissolved, while 

 the red remained unaltered,the colour only becoming deeper. 

 After washing and drying in a very strong heat, 10 grammes 

 of this red lead were ignited in a weighed platina dish ; they 

 lost -29 tir. The oxide, which had become yellow, was 

 now dissolved in vinegar; the sulphate of lead and silica 

 which were left in tliis process, weighed when ignited -135 

 gr. To the solution in vinegar nitrate of silver was added, 

 and '01 gr. of muriate of silver was precipitated, which 

 answers to -03 gr. of submuriale of lead ; so that in the 

 whole there was -l65 of foreign matter. Consequently 

 A 4 9'835 gr. 



