274 
POWER OF LITHARGE, ETC. 
chanically in the phenomenon of the exfoliation of the 
litharge. 1 " 
It is proper to point out the fact that all those circum- 
stances that tend to diminish the rapidity of the cooling pro- 
cess, and the solidification of the litharge, have also a ten- 
dency to increase the proportion of red litharge that is 
formed; when it is poured into vessels of insufficient capa- 
cities, the litharge cools too quickly, and remains yellow, 
and without exfoliation. 
M. Fournet admits that red litharge contains more oxy- 
gen than yellow, and that it owes its color to a certain pro- 
portion of minium, a portion of which many specimens have 
exhibited the undoubted presence of. 
M. Thenard, and most chemists, also, attribute the color 
of the litharge of commerce to the presence of a small 
quantity of minium. 
Without wishing to deny that litharge, when slowly 
cooled, cannot, under certain circumstances, absorb oxygen 
and form minium, a well established fact I think, neverthe- 
less, I am able to demonstrate that another explanation 
must be found for the exfoliation of the masses of litharge, 
and the production of red litharge. The following are the 
experiments on which I think 1 can rest this assertion : — 
1. The red litharge I have examined gave out no oxy- 
gen by heat. 
2. The same litharge tried with much care by pure 
nitric acid, furnished me with no puce-coloured oxide ; a 
minute portion of minium added to yellow litharge, scarcely 
modifying its tint, could be discovered under the same cir- 
cumstances. 
3. The red litharge, heated to a temperature at which it 
gave out no oxygen, and thrown suddenly into water, be 
came yellow, 
* The first pots of litharge that are collected do not always exfoliate; 
nevertheless, I have proved that they sometimes contain oxygen in 
the state of gas^ although in small quantities. 
