74 
ON WHITE LEAD. 
two atoms of carbonate of lead and one atom of hydrate, 
but I do not know whether he experimented on white 
lead precipitated by carbonic acid among the rest ; the 
probability is that he did, for the process is evidently similar 
to the older method, in which a fermenting material is em- 
ployed. 
The carbonate of lead formed by these processes, whether 
similar or not in composition to the ordinary kinds, differs 
in one essential point, that it will not cover as well, and has 
less body; and Dr. Ure appears to have first pointed out the 
cause of this defect; for on examining it microscopically, he 
found it to consist of small crystalline particles, with a certain 
degree of translucency. White lead produced by the older 
methods is superior to it in these respects, which Mr. Ben- 
son, and I think justly, refers to "its never having departed 
from the solid state," and that the particles "have not been at 
liberty to arrange themselves symmetrically." In his patent, 
therefore, (fourth) he employs a quantity of moisture just 
sufficient to determine the action of the carbonic acid. It is 
said that Messrs. Gossage and Benson produce forty tons of 
excellent white lead per week, (Ure's Diet.) La Societe d' 
Encouragement made a large number of experiments on the 
various kinds of white lead, and came to the conclusion that 
that produced by precipitation will cover as well as the others, 
but requires more coatings, that it has a degree of translucen- 
cy, but that it is whiter than that made by the older pro- 
cesses." (Diet, de V Industrie, &c, tome iii., p. 164.) It 
may be that this defect of body may be remedied by violent 
agitation during the process of precipitation, which would dis- 
turb the crystallization. If so, the third patent should pro- 
duce a dense material, and it is probable that the violent stir- 
ring in the fourth may have this effect in addition to its expos- 
ing a greater surface to the action of the carbonic acid. We 
shall dismiss the fifth patent with the remark that the extent 
of apparatus required is decidedly objectionable, and that it is 
inefficient, since the liquid must be pumped up several times, 
