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Simple Test for White Lead

These are sulphides of cadmium, and, when Take a piece of firm, close-grained charcoal, well prepared, are very stable; they can be and, near one end of it, scoop out a cavity used in fresco and silicious painting. It is about inch in diameter and 4 inch in depth. mentioned elsewhere that cadmium sulphide Place in the cavity a sample of the lead to be decomposes emerald green. (See No. 2712.) tested, about the size of a small pea, and apply It is not safe to use it with lead pigments, unto it continuously the blue or hottest part of less it has been most carefully prepared; and the flame of a blow-pipe; if the sample be here, inasmuch as decomposition may take strictly pure, it will in a very short time, say place, and lead sulphide, which is black, be in 2 minutes, be reduced to metallic lead, leaving no residue; but if adulterated to the extent of 10 per cent. only with oxide of zinc, sulphate of baryta, whiting or any other carbonate of lime (which substances are now the only adulterations used), or if it be composed entirely of these materials, as is sometimes the case with cheap lead, it cannot be reduced, but will remain on the charcoal an infusible mass.

Itis well, after blowing upon thesample, say for formed, it is better to avoid the mixture; no such mixture can occur in fresco or silicious painting, and it would be well if there were no chance of its occurring in any other style of painting, by the banishment of white lead from the list of artists' pigments. No other salts of cadmium are important as pigments.