72 
ON WHITE LEAD. 
portion of new material being added each time to allow for 
accidental loss and waste. All subsequent patents based on 
a similar principle were derived from the above patent, which 
was carried out on a large scale by MM. Roard and Brechoz. 
At this day a large portion of white lead used in France and 
Sweden is similarly manufactured, and the process is also em- 
ployed in Germany, England, and at one establishment in 
this country, in Brooklyn, New York. It is generally be- 
lieved that the old processes for manufacturing white lead by 
using fermenting tan, &c, and that in which vinegar, air and 
carbonic acid are driven into chambers containing lead and vi- 
negar, are governed by different principles, but it will be 
shown that they are essentially the same with those where 
carbonic acid is passed through a subsalt of lead. 
Jl. Precipitating Processes. — 2. It was stated that G. F. 
Hagner obtained a patent in 1817 for manufacturing white 
lead by attrition, but that the quality of the material being 
inferior, the proprietors varied the apparatus and process in 
such a manner as to approach Thenard's method. For a more 
minute description of their plan, see Jour. Frank. Inst., vol. 
i., 3d series, p. 158. They forced carbonic acid through a 
mixture of litharge, pulpy oxide produced by attrition, and 
vinegar, and their white lead was of such a quality as to re- 
ceive a medal in 1826. 
3. Button and Dyar took out a patent for making white 
lead, the specification of which will be found in Rep. Pat. Inv., 
vol, x., 1838, with a drawing illustrating the apparatus. They 
employed purified carbonic acid from the combustion of coke, 
which was passed through a mixture of litharge and nitrate of 
lead dissolved and suspended in water, and kept at the boil- 
ing point of water in the state of agitation by the issue of 
steam in the bottom of the decomposing vats. The carbo- 
nate as it is formed was drawn up by a pump, suspended in 
water, and falling on a filter, where it remained, suffered the 
liquid to fall through into the first vat. 
4. In the Jour. Frank. Inst., vol. xxv., p. 197, are remarks 
on the manufacture of white lead by Mr. Benson, who is 
