70 
ON WHITE LEAD. 
its very diffused state usurp the place of much of the hy- 
drate. 
When vinegar is introduced in these processes, another 
operation takes place, which induces the more rapid forma- 
tion of an oxide of lead, preventing at the same time the for- 
mation of as much hydrate, and the acetate which forms be- 
ing simultaneously decomposed by carbonic acid, the vinegar 
as rapidly passes to another portion of oxide. 
In Bonsdorf's experiments the hydrocarbonate was tried as 
a pigment and found to possess little body, a circumstance 
which will probably hold good with nearly all white lead 
made by the above processes, excepting the last, and the modi- 
fied operations of the first patent. In the fifth patent carbo- 
nic acid is forced in with atmospheric air, and probably acts 
in part catalytically by inducing the formation of oxide, and 
in part by uniting with the oxide "in its nascent state," and 
thereby preventing the formation of as large a quantity of hy- 
drate. It is said, moreover, that the white lead thus obtained 
is equal to that manufactured by the older processes, (Jour. 
Frank. Inst, vol. xxvi., p. 125,) but I question whether it 
will be found to contain the requisite quantity of carbonic 
acid to prevent its liability to become yellow. It remains to 
be seen, however, whether by any one of these processes, in 
which trituration of metallic lead is the chief point, the min- 
gled hydrate and carbonate of lead contains a sufficient amount 
of carbonate to prevent its becoming yellow by employment 
as a pigment; for that was the chief difficulty experienced by 
the first patent, and probably will be an objection to all the 
others; and it will be shown below that the more highly car- 
bonated the lead is, the less it is subject to this change. The 
economy of the process of attrition certainly demands atten- 
tion, as well as the simple arrangements by which it may be 
effected, but then the question returns, whether the tendency 
to become yellow by exposure to the atmosphere, or of va- 
pors, can be obviated by giving the highest dose of carbonic 
acid, partly by driving that gas through the apparatus, and 
partly by introducing another ingredient into the water em- 
