Intelligence and Miscellatieoiis Articles. 237 



ON MINIUM. BY M. LEVOL. 



Although minium has been an object of research by several chemists, 

 opinions are still divided, not only as to its analysis, but also as to 

 the manner in which its true constitution ought to be represented. 



M. Levol states that, having had occasion to examine several 

 samples with respect to the commercial value, his experiments tend 

 to confirm the views generally entertained Avith respect to this sub- 

 stance, namely, that it is not a peculiar oxide, but a definite compound 

 of protoxide and peroxide. 



M. Levol agrees with M. Dumas, and it may be added also, with 

 the previous determination of Dalton, that the comjiosition of minium 

 is represented by Pb O'^ + 2 Pb O, and he finds that this is also its 

 composition obtained by the two following new processes : 



The first consists in calcining, in a platina or silver crucible, a 

 mixture of 100 parts of protoxide of lead, prepared by calcining the 

 carbonate, 25 of chlorate of potash, and 200 of nitrate of potash ; 

 this last salt is employed for the purpose of rendering the mixture 

 fluid, without occasioning loss of chlorate of potash. 



In operating in this way, the action of the oxygen upon the oxide 

 of lead is so effectual, that it is converted into peroxide ; and this 

 oxide may be thus procured with the greatest readiness. If the 

 operation be carried on till the mixture becomes nearly red-hot, the 

 swelling diminishes, the mass thickens, and minium is formed. It 

 is sufficient to boil the residue in a solution of potash or soda, and 

 to wash it well, in order to obtain pure minium of the composition 

 above stated. The product is in a state of minute division, of a fine 

 red colour, with a shade of orange, like the finest minium obtained 

 in commerce. 



Minium may also be obtained in the moist way, by boiling for an 

 hour or two a solution of an alkaline plombate with binoxide of lead 

 in fiue powder; the colour of the binoxide becomes gradually lighter, 

 and eventually an ochre-red powder is obtained ; this is merely mi- 

 nium, mixed with a little binoxide, which has escaped the action of 

 the plombate ; it is easily got rid of by digestion in a solution of 

 oxalic acid, which decomposes the peroxide without acting upon the 

 compound, and the oxalate of lead is afterwards separated by pot- 

 ash. The product thus obtained has always a deeper red tint than 

 that of the minium prepared in the dry way; but it becomes brighter, 

 and more nearly resembles the latter when it is triturated with 

 water ; their composition is similar, and the difference of colour ap- 

 pears to be entirely owing to texture ; there is, in fact, some appear- 

 ance of crystallization in the minium obtained in the moist way. 



M. Levol's analyses were performed by putting the minium into 

 excess of nitric acid of sp. gr. ril4, and agitating the mixture fre- 

 quently during twenty-four hours ; the temperature must not be 

 raised by tiie action, or otherwise a portion of the binoxide is decom- 

 posed, and a small quantity is even dissolved, which gives the solu- 

 tion a violet colour. It remains after this operation merely to weigh 

 the residual binoxide, and to determine that it was totally soluble in 

 protomtratu of mercury, which does not act upon minium. 



