MISCELLANY 
Note on Minium. — Although minium has been the object of the re- 
searches of many chemists, opinion is yet divided as to the true mode of 
representing its composition, and even as to its analysis. Having occa- 
sion to examine several specimens, with regard to their commercial value, 
the observations that were then made, induced me to undertake the expe- 
riments, of which I offer here the following results ; I do this with the 
more confidence, because they appear to me to afford additional support to 
the opinion which considers minium, not as an oxide distinct from the two 
oxides PbO and PbOs, but rather as a combination of these two oxides in 
a constant and definite proportion. 
The most important investigations which have been made, in a scien- 
tific point of view, with regard to minium, are those of M. Dumas, 
from which it results, that this product has always the following compo- 
sition: 
Pb02+2PbO, 
when properly purified and saturated with oxygen. It is likewise this 
proportion which I have constantly found in analysing miniums under 
new circumstances, and by the two different processes which I am about 
to describe. 
The first consists in calcining, in a crucible of silver or platinum, a 
mixture of 100 parts of protoxide of lead, the product from calcined white 
lead, with 25 parts of chlorate, and 200 parts of nitrate of potassa ; the ob- 
ject of this latter is, to give greater fluidity to the mixture, without increas- 
ing the amount of chlorate. 
By operating in this manner, the action of the oxygen upon the oxide of 
lead is so efficacious, that it is changed into peroxide ; this oxide may 
thus be procured with great facility. If we proceed farther, if the tem- 
perature be elevated to an obscure red, the effervescence diminishes, the 
mass thickens, and minium is perceived to form.* It is sufficient to boil 
♦It is necessary to continue the elevation of the temperature until it commences 
to decompose in some points towards the sides, so as to be certain that no peroxide 
remains. If the object is to prepare this latter oxide, it is necessary to withdraw the 
VOL. VII. — NO. II. 22 
