Mr. R. Phillips on Minium. 127 



mitted to three calcinations gave a fine orange minium, con- 

 taining 9*24 per cent, of oxygen ; this, however, he observes 

 is still below the proportion required to constitute the lead a 

 sesqui-oxide, and which, in fact, amounts to 10*38 per cent. 



M. Dumas states minium of the eighth operation to consist of 

 74 protoxide, and 26 peroxide; that obtained by calcining 

 white lead, of 66*8 protoxide, and 33*2 peroxide; and pure 

 minium he considers as equivalent to 65*1 of protoxide with 

 34*9 of peroxide. 



I shall now state the results of my own experiments on 

 minium; that which I used appeared to be free from carbo- 

 nate of lead, and was moderately dried before submitting it to 

 the following experiments: — Two hundred grains were di- 

 gested in an ounce of strong nitric acid, diluted with half a 

 pint of water; 49*6 grs. of peroxide were left, consequently 

 the minium was separated into 



Protoxide of lead 75*2 



Peroxide of lead 24*8 



100-0 

 I also boiled some of the minium with excess of moderately 

 strong acetic acid ; by this operation it was separated into 



Protoxide 74*2 



Peroxide , 25*8 



100-0 

 These results do not differ much ; but taking the mean, we 

 have minium resolved into 



Protoxide 74*7 



Peroxide 25*3 



100-0 

 Now this result differs considerably from that obtained by 

 Dr. Dalton; he procured only 20 per cent, of peroxide. The 

 cause of this difference is readily explained by referring to 

 M. Dumas' s Table of Experiments ; from which it appears 

 that minium of the third calcination yields only 20*3 percent, 

 of peroxide; while that of the eighth gives 26 per cent. Dr. 

 Dalton appears to have employed a specimen of the former, 

 while I used one of the latter. 



In order to determine the proportion of pure minium in the 

 specimen which I used, I added separate portions of 200 

 grains each, to the annexed quantities of strong acetic acid, 

 diluted with half a pint of water; viz. one, two, two and a half, 

 and three drachms. I found that the minium digested in the 

 first lost 22 per cent.; in the second 27*5 ; and in the third 



