ON THE OXIDES OF LEAD. 289 



of their weight, and are converted into yellow oxide: Thefeojtide; eafily 

 nine grains are oxigen gas. Hence brown oxide is compofed ' ^"S'''S='*' 

 df 91 yellow oxide and 9 oxigen. But 91 of yellow oxide 

 contain 9.4 of oxigen. Therefore 100 parts of brown oxide 

 are compofed of 



81.6 lead, 



18.4 oxigen. 



100. 

 3. Mr. Prouft, from his experiments, Hates the proportion 

 of oxigen in this oxide at 21 pei- cent. If we take tiie mean 

 of the two refults, we obtain 19.7. We rnay, therefore, lay 

 down 20 per cent, as tluj proportion of oxigen in brown oxide 

 of lead : This cannot deviate far from the truth. 



IV. Red Oxide. 



Red lead being one of the moll common of pigment, is un- Red lead i 

 known, I prefume, to no perfon. The method of manufac- 

 turing it has been defcribed by Dr. Watfon in his Chemical 

 Effaj/s, by Jars in the Memoires of the French Academy for 

 1770, and by Ferber in his Mineralogy of Derbydiire. 



J. It is a taftelefs powder, very heavy, and of an intenfejts chirailers j 

 red colour, often inclining to orange. I have never met with 

 any fpecimens of it abfolutely pure, but not unfrequently the 

 foreign bodies do not exceed one or two per cent. They 

 coniift of feven grains of fand and oxide of antimony. Dr. 

 Watfon found traces of filver in it. It lofes no fenfible weight 

 in a heat of 400". 



2. When 50 grains of red lead are digefted in diluted nitric contains 28 lead 

 acid, they leave 12 grains of brown oxide. The folution eva- + ^* oxigen j • 

 poraled to drynefs, yields 56 grains of nitrate of lead. Now, 

 5Q grains of nitrate contain 3S.36 grains of yellow oxide. 

 Red lead, therefore, is compofed of 33.36 yellow oxide and 

 12 brown oxide, or, per cent, of 



76.72 yellow oxide, 

 24.00 brown oxide. 



100 72 

 The excefs muft be afcribed to the imperfeaion of our me- 

 thods. I (liall omit it in the calculation: Not that red lead 

 Vol. VIII.— August, 1804. U is 



