ON WHITE LEAD. 
73 
probably the same one engaged with Mr. Gossage in the ma- 
nufacture, near Birmingham, England. According to their, 
patent, they employ of vinegar -§-1^ of the weight of litharge, 
and add so much moisture to the latter that it merely "feels 
sensibly damp to the touch." Heated carbonic acid (from 
coke) is passed over this mixture in stone troughs, while the 
contents are powerfully stirred up, (Ure's Diet.) 
5. Cory's patent in Rep. Pat. Inv., vol. xii., 1839, employs 
carbonic acid derived from a lime-kiln, introducing it into 
a chamber, the upper part or ceiling of which is perforated 
with numerous small holes. A solution of subacetate of lead 
is pumped up to the roof of the chamber and falls through the 
small holes like a shower, absorbing carbonic acid in its de- 
scent. 
These are the principal variations in the precipitating me- 
thod of Thenard; all are referable to the same theory, viz., the 
decomposition of a subsalt of lead by carbonic acid. The last 
is evidently the same, excepting that the operation is inverted, 
and instead of passing carbonic acid through the solution, the 
latter drops through an atmosphere of the acid. The second 
is somewhat analogous to the fourth patent, excepting that the 
latter prescribes less moisture and employs heated carbonic 
acid. In both, the acid operates by forming carbonate of 
lead from a part of the oxide in the basic acetate, while the 
latter, becoming more neutral, is acted upon by the excess of 
litharge, forming again the basic acetate, which is again de- 
composed. The third patent employs a basic nitrate of lead, 
i. e. nitrate of lead and litharge, instead of an acetate, which, 
together with the boiling state of the solution, constitutes its 
difference from the others. 
According to the observations of Robiquet, Pfaff, and 
others, the carbonate of lead obtained by precipitation with 
carbonic acid is a neutral salt, consisting of one atom each of 
acid and base, the only water present being hygroscopic. In 
the Bullet, d. Sciences, &c. en Neerlande, vol. L, p. 302, Mul- 
der has shown that the white leads of commerce consist of 
VOL. VIII. — NO. I. 
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