44 
SELECTED ARTICLES. 
That taken by the lead to pass to the state of protoxide, 
will then be 0.265 — 0.199 = 0.066, that is to say, exactly 
one-third of the quantity taken by the sulphurous acid in 
changing to sulphuric acid. We know, likewise, that on eva- 
porating to dryness the solution of lead in muriatic acid, the 
neutral sulphate of lead is regenerated. This salt then con- 
tains three times more oxygen in the acid than there is in the 
base. 
5. Finally, the examination of a metallic compound by 
means of the mode which I have pointed out, will always 
serve to verify an analysis, when we know the nature of the 
products which should result from different bodies submitted 
to the action of an aqua regia, formed from the peroxide of 
manganese and hydrochloric acid. Thus we know that sul- 
phur is always found in the liquid as sulphuric acid, arsenic 
as arsenic acid, and iron as a peroxide, &c. The quantities of 
oxygen which each of the bodies should take in the reaction, 
ought to be equal to the number given in the analysis. The 
products of the arts produced by the treatment of metals ex- 
tracted from their sulphurets, or arseniurets, often contain 
very variable combinations of the oxides with the sulphurets. 
The separation of the different elements of these bodies in- 
completely oxidized, present difficulties, and it is evident that 
the exact determination of the whole of the oxygen absorbed 
by the bodies in dissolving would afford a valuable datum in 
discussing the results obtained by analysis. 
Jinnales des Mines. 
