290 ON THE OXIDES OF LEAD. 



is a mixture of yellow and brown oxides, but that it contains 

 all the lead and oxigcn in the above proportions of thefe 

 bodies. Now 



76 grains yellow oxide is compofed of 63.8+ 7.2 

 24^ grains brown oxide of - - - 19.2-j- 4.8 



Therefore red lead is compofed of - 88. -{-12. =10(>. 

 not eafily de- 3. It is well known that red lead gives out oxigen gas when 



KeTchMU ^ heated, and that it approaches to the ftate of yellow oxide. 

 The lofs of weight ought to give us' the portion of oxigen 

 which it contains more than is neceffary to conftitute it yellovr 

 oxide : But, upon trial, I could obtain no fatisfaftory refults 

 this way. In one experiment 100 grains of red lead loft 4i 

 per cent, in another feven per cent. The experiments were 

 made in fmall covered earthen-ware crucibles. The oxide 

 was melted into a dark-brown tranfparent glafs, not unlike 

 glafs of antimony, but much harder. On breaking this glafs, 

 I found in it globules of lead reduced to the metallic ftate : 

 This accounts in part for the lofs of weight, and (hews us alfo, 

 contrary to the opinion of cheraifts, that the red oxide of lead 

 is reducible, at leaft in part, by mere heat. In all probability 

 nothing prevents the complete reduction but the readinefs with 

 which it unites with the vetTel in which the experiment is made. 

 I twice varied the experiment, by enclofing the fmall earthen 

 crucibles containing the red lead in a crucible of platinum ; 

 but in neither cafe did I obtain any vifible metallic globules; 

 yet the lofs of weight was the fame. This renders it probable 

 that a portion of lead had been reduced and afterwards difFufed 

 through the oxide. 

 Not foluble as 4. The red oxide of lead does not feem capable of com- 

 rf^ /.Win acids, {jjj-jjj ^^jjj, ^cids. Many acids indeed a£t upon it, but they 

 nor in alkalis, , , . , , . . , „ .- !• , m. 



always begin by reducmg it to the Itate or yellow oxide. The 



fixed alkalies do not alter its colour, but they gradually diflblve 

 it. From this folution it is thrown down always in the ftate of 

 yellow oxide ; Hence it muft lofe oxigen during the folution^ 



V. Litharge. 



Though litharge is very far from being the fame with red 

 lead, yet, as the mode of preparation is analogous, a iew re- 

 marks on it may not be improper in this place. 



Litharge 



