Lead is an important and costly ingredient of flint-glass, used as a
protoxide, either as litharge or red lead, and should be perfectly
pure, for the presence of any other substance or metal will be shown in
the color of the glass. Consequently, the purity of the glass depends
mainly on the quality of the metallic lead and its being well
manufactured.
The writer believes he was the first person in the United States, aided
by a director of the New England Glass Company, to build a lead
furnace. This was in 1818. His only guide was a volume of "Cooper's
Emporium of Arts and Sciences," which furnished a plan on a very
limited scale.
The furnace proved successful, and enabled the Company to continue
their manufacture of glass at a period when no foreign red lead was to
be procured. They enlarged their works, until they have become the most
important in the country; while for over thirty years they monopolized
the business in all its branches, from the highest qualities of pure
Galena and painter's red lead to common pig lead. In manufacturing
metallic lead, its weight is materially increased by the absorption of
oxygen gas. In 1847 the writer made many test experiments, one as
follows: 660 pigs of blue lead, weighing 45,540 pounds, turned out from
the ovens 48,750 pounds of litharge,--an increase in weight of 3210
pounds.
The cost of labor was $65.50; fuel, $86.50; engine power, $17.50;
total, $169.50; and the market value of the excess in weight of the
lead was $250, showing a satisfactory profit to the company for their
outlay in this branch of their business. Chemistry gives the increase
in course of manufacture: In protoxide state, 7 per cent.; in deutoxide
state, 11 per cent.; in tritoxide, 15 per cent.
Muriatic acid will detect iron in lead, on dissolving a small piece of
lead in the acid. If colorless, it is good.
Nitric acid will detect if there is cobalt in the lead, by adding to
the acid half the quantity of high-proof alcohol. If present, the
evidence is soon seen.
Some use the following as more direct:--In a small evaporating glass
dish place say one ounce of lead; cover it with muriatic acid; dissolve
the lead over a spirit lamp, add a little water, and let it settle;
draw it off into another glass vessel, and add five or six drops of the
solution of potash. If the lead is suitable for glass-makers, the
solution will be of a light, clear, greenish color; if of a blue or
purple shade, it is not suitable for flint-glass.