ON WHITE LEAD. 
81 
A portion of white lead manufactured according to Clark's 
process was exhibited at the Franklin Institute last Fall, and 
pronounced equal to the others, it not being known at the 
time that it was thus manufactured. A sample of Richards' 
is in the Technical Cabinet of the Franklin Institute. 
The main question relative to the newer processes touches 
their economy, a point which we do not propose to discuss, 
as foreign to the nature of this essay. Certainly they offer 
greater neatness of arrangement, and avoid the heavy losses 
from breakage of pots, while the materials employed are eco-^ 
nomical, but then again they require their peculiar expendi- 
ture for the production of carbonic acid and steam. 
///. Processes dependent on double elective affinity. — » 
The principle of these processes is not novel, although va- 
rious patents have been taken out latterly based upon it, de~ 
pending on the precipitation of a salt of lead by a carbonated 
alkali. Some are simple, others of a very complicated cha- 
racter, as the following selections will show. 
Hemming's Lond. Jour., vol. xii. Nitrate of soda is de= 
composed by sulphuric acid, by which nitric acid is obtained, 
and sulphate of soda. The sulphate of soda is decomposed by 
charcoal, chalk, &c, and a carbonate of soda produced. The 
nitric acid first obtained is employed to form a nitrate with 
lead or its oxide, and this in solution is precipitated by the car^ 
bonate of soda. Thus we have obtained a carbonate of lead 
and nitrate of soda, the latter of which is again decomposed as 
above. To say the least of it, the process is highly ingenious, 
and involves not a little chemical knowledge, while, like 
Thenard's process, the original salt is recovered, except an 
allowance for accidental waste. 
Watt & Tebbutt's patent, Lond. Jour., vol. xiii. Chloride 
of sodium (common salt) and litharge are heated to make 
chloride of lead. Three parts of the latter are mingled with 
one of red lead, and sulphuric acid added, while steam heat is 
applied. There remains sulphate of lead, and chlorine is 
evolved. The sulphate is then treated with carbonated alkali, 
which, according to the patent, will make hydrate with a little 
VOL. VIII. — no. i. 11 
