POWER OP LITHARGE, ETC. 
275 
This experiment shows that the variations in the struc- 
ture and colour of litharge, according to the circumstance 
of temperature that accompany its production, do not de- 
pend on changes in chemical composition, but much on 
modifications arising out of isomerism or dimorphism, like 
those that cause the difference between vitreous arsenious 
acid, and opaque arsenious acid, barley-sugar and sugar- 
candy, red iodide, and yellow iodide of mercury, &c] 
These modifications in the structure and color of protox- 
ide of lead have a relation to the density of the specimens. 
According to the experiments I have made, red exfoliated 
litharge is less dense than yellow crystallised litharge. 
Figures having connection with various experiments made 
for this purpose, will be found in my Memoirs. 
In fine, the facts related in this note appear to me to es- 
tablish — 
1. That oxygen can be dissolved by litharge in a state 
of fusion, as it is dissolved in silver, and that it does not 
form a super-oxidized combination : the nitrogen dissolves 
in it, perhaps in a small proportion. 
2. That physical differences of structure, color, and densi- 
ty alone exist between yellow and red litharge, which make 
no alteration in their chemical composition. The different 
varieties may be produced at will by a dry process, accord- 
ing to the circumstances of temperature, and the quick- 
ness of the cooling of the mass. — Ibid, from Jour, de 
Phar. 
