170 
MISCELLANY. 
the residue with a solution of caustic potassa or soda, and afterwards to 
wash it well to obtain pure minium, with the composition before indicated. 
The product is in a minute state of division, of a beautiful red, slightly 
bordering on orange, like the best miniums of commerce. 
Minium may also be obtained in the moist way, by boiling, for one or 
two hours, a solution of an alkaline plumbate, with deutoxide of lead in 
fine powder;* the color of the deutoxide gradually changes, and finally 
becomes an ochreous red powder. This powder is nothing else but mi- 
nium, commonly contaminated with a small quantity of deutoxide which, 
has not been affected by the alkaline plumbate; it may readily be freed 
from this by digestion with a solution of oxalic acid, which destroys the 
deutoxide without attacking the compound, and the oxalate of lead may after- 
wards be separated by caustic potassa or soda. The product thus obtained, 
has always a red tinge, more deep than that of minium prepared in the dry 
way, but it becomes lighter, and approaches it more when triturated with 
water; otherwise, it has exactly the same composition as minium, and 
the difference in the tint appears due solely to the difference of texture; in 
fact, there is somewhat of a crystalline appearance in the minium obtained 
in the moist way. 
My analyses were made by keeping the miniums in contact with an excess 
of nitric acid, of 15° B.,for 24 hours, and shaking frequently, without any 
increase in the temperature, which would decompose a portion of the 
deutoxide, which dissolving even in small quantity, would color the 
liquid of a violet. It only remains, afrer this treatment, to dry the resi- 
due and weigh, taking care to ascertain that it is completely soluble in 
proto-nitrate of mercury, which has no action on minium. 
The motives which induce me to admit, as the most likely, the opinion 
that minium is a combination of the two oxides, are the following : 
Admitting that minium is a peculiar oxide, intermediate between these 
two oxides, the fact becomes inexplicable, that protoxide is, by calcina- 
tion with chlorate of potassa, readily converted into deutoxide, while I 
have satisfied myself that minium cannot, in this manner, be changed into 
deutoxide. 
crucible, when the matter has acquired a black tint, of a uniform color, which com" 
monly happens -with the proportions mentioned, when the whole mass of the 
mixture is in full fusion ; it is thus easy to convert into pure peroxide, at least nine- 
tenths of the protoxide of lead used, by treating with nitric acid, the residue, 
after having been well washed. The peroxide of lead, thus obtained, is nearly 
black. 
* We may employ the pure plumbate, but it is more convenient to use a solution 
obtained by dissolving in water five or six parts of crystallized nitrate of lead for one 
of deutoxide, to which is to be added caustic soda or potassa, in sufficient quantity to 
redissolve the hydrate. 
