Substitutes for White Lead.

Popular Science, heinäkuu 1895

Only two substances at present manudactured are regarded by Mr. A. P. Laurie as satisfactory substitutes for white lead in painting - sulphate of lead and oxide of zinc. Sulphate of barium has hardly any covering power, and sulphide of zinx, though remarkable for covering power, has not proved, as at present manufactured, a durable pigment. Oxide of zinc, though deficient in covering power, is remarkably white, and preserves its color in impure air. Sulphate of lead is in the market in two forms- sublimed sulphate, which is prepared directly from galena; and precipitated sulphate, ground by Freeman's patent with oxide of zinc, and sold as Freeman's white. Sulphate of lead prepared by sublimation has much more covering power and is much denser than precipitated sulphate. Another pigment sold as a harmless white lead is prepared in a similar way by grinding together oxide of zinc and sulphate of barium. in quantity of oil required the substitutes named compare well with white lead, some taking a little more and some a little less, except oxide of zinc, which takes a very large quantity. in the matter of susceptibility to impure air, they all have a distinct advantage over white lead. Zinc oxide is not at all affected, and the sulphate is very slightly affected unless the gas is in very large quantities and the paint is wet. in durability under outdoor exposure they are not better than white lead, except that oxide of zinc remains white. in their appearance in oil they differ considerably from white lead, being thin and stringy instead of stiff and firm, and this is against them. But Mr. Laurie does not find that when thinned down they seem to differ appreciably from lead carbonate in ease of working. in their effects on health, oxide of zinc is harmless. Sulphate of lead is not absolutely insoluble in very weak hydr och loric acid, and may therefore be slightly soluble in the stomach and to some extent poisonous; but the author does not believe that under ordinary conditions of manufacture or use it would produce lead poisoning.

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