78 
ON WHITE LEAD. 
quantity is small, this will be a subsalt. But there is carbo- 
nic acid also present, and the material must be moist enough 
to determine its action in decomposing the acetate; while the 
acetic acid, thus slowly disengaged, will act similarly on 
another portion of the metal, or its oxide. To this it may be 
objected, that at length there will be a neutral salt formed, 
which the carbonic acid cannot decompose. It is, however, 
shown that this acid will decompose even the neutral salt to 
a certain extent, when it is in solution. It is not, however, 
necessary to suppose this, for during the length of time re- 
quired for the conversion of the lead, the whole of the vine- 
gar might be evaporated without its being noticed by its 
odour above the bed to any appreciable extent, and as each 
successive portion of acetate is decomposed, a portion of the 
acid may thus be volatilized and escape into the atmosphere. 
Another explanation of this presently appeals. That acetate 
of lead is thus formed is shown from the amount of it lost up- 
on washing white lead, which is so great that it becomes a 
question with the manufacturer whether it might not be re- 
extracted as acetate, or better in some other form. It may be 
farther objected that if carbonic acid is thus employed to de- 
compose the generating acetate, why will it not do it, when 
a piece of the lead in a pot dips into the acid, for in this case 
only acetate is the result. To this may be answered that from 
the known superior energy of the acetic acid, it forms an 
acetate with great rapidity, the small crystals of it below 
acting with capillarity to convey the acid to the upper por- 
tions of the metallic coil, while the slowly disengaged carbonic 
acid can affect the merely moistened crystalline mass with 
difficulty, and certainly not materially, excepting on its sur- 
face. The conclusion, then, is that the process is substantially 
the same as in Thenard's method, after the lead is oxidized 
by a moist atmosphere, viz., that a sub-acetate is formed 
which is simultaneously decomposed by carbonic acid, and 
that the more neutral salt thus generated being again ren- 
dered basic by another portion of oxide is again decomposed, 
while the final formation of an acid salt is prevented by the 
