Brass.
[19]—The malady the brass caster has suffered from in the past is par excellence brassfounders’ ague. Lead, however, is introduced (rarely exceeding 10 per cent.) for the purpose of softening the alloy of copper and zinc. Of 77 cases of lead poisoning in the ten years 1900-1909 included under the heading “Brass,” 38 were polishers, 28 casters and others, and 11 chandelier fitters. Cases occur among the casters probably from inhalation of the fumes in pouring, and among the polishers from inhalation of the small proportion of lead in the dust given off in the absence of adequate exhaust. In a factory where there were two emery wheels, one with a hood and fan to carry the dust away, while the other remained unprotected, the worker at the unguarded wheel suffered from lead poisoning. In filing and dressing the article is held in a clamp with leaden claws, which gradually become worn away, just as does the lead bed used by the file-cutter. This may account for the poisoning reported among filers and dressers.
A sample of dust taken from under a calico mop for brass polishing was found in the Government laboratory to contain 2·1 per cent. of lead.
The joints of chandelier fittings are sealed with a white lead paste. Instead of always testing the completeness of the seal by means of an air pump and pressure gauge, the fitter frequently tests it by applying his lips to the unsealed end and blowing through the pipe. All the cases among chandelier fitters are caused in this way—perhaps the clearest instance of poisoning by absorption through the alimentary canal, as distinguished from absorption through the lungs, that can be cited. While use of an air pump and immersion of the joint in water or pressure gauge only is an entire protection, and should be provided wherever this work is done, constant supervision as to its use is called for. The sealing of the joint can be done with a material known as “caulkite,” containing neither white nor red lead.
For references, see [end of Chapter XVII.]
CHAPTER XVI
DESCRIPTION OF PROCESSES—Continued
Manufacture of White Lead.
[20]—The usual method in this country is that known as the “Dutch process,” although the German chamber process, precipitation processes, and others, are all practised.
Dutch Process.
—A layer of spent tan is placed on the floor of the stack (a chamber with walls of brick some 25 feet high, and a vertical opening from top to base through which the men enter), upon which are arranged earthenware pots partially filled with dilute acetic acid. Strips of lead are then placed on small square “cockney” pots, or more rarely in the form of folded grids, inside deep, long “castle” pots, and the whole covered with boards, resting on special “bearer pots” containing dilute acetic acid. Ten to fifteen of such layers (blue beds) one on the top of the other are built into the stacks to a height of some 20 feet. When completed, the stacks remain for 80 to 100 days before being emptied. During this period the temperature rises to 75° to 80° C., considerable evolution of carbonic acid gas takes place, and the lead is converted first into acetate and subsequently the white basic carbonate. The layers (white beds) are uncovered and the corroded strips (corrosions) collected by hand. They are placed in trays and carried to heavy steel rollers by means of which and subsequent raking in wash becks the carbonate is detached from the uncorroded central core of blue lead. In many factories corrosions are now conveyed from the stacks to the wash becks or rollers by travelling cranes. The recovered blue lead is removed in a wet state to be remelted and recast. The corrosions, after passing through the rollers and wash becks, are shovelled on to a picking-board and transferred gradually to the grindstones. From the stones the ground pulp passes to the settling becks through several gratings of fine copper mesh. In the form of pulp the material is ladled by hand into bowls for conveyance to the drying stoves. When dry, the contents of the bowl are emptied into barrels and headed, or into hoppers, from whence the material is conveyed to be packed either by hand or automatically by mechanical packers, or to be converted into paint.