2695. Simple Test for White Lead

2695.     Simple Test for White Lead. Take a piece of firm, close-grained charcoal, and, near one end of it, scoop out a cavity about 1/2 inch in diameter and 1/4 inch in depth. Place in the cavity a sample of the lead to be tested, about the size of a small pea, and apply to it continuously the blue or hottest part of the flame of a blow-pipe; if the sample be strictly pure, it will in a very short time, say 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. It is well, after blowing upon the sample, say for 1/2 a minute, by which time the oil will be burned off, to loosen the sample from the charcoal with a knife blade or spatula, in order that the flame may pass under as well as over and against it. With proper care the lead will run into one button, instead of scattering over the charcoal, and this is the reason why the cavity above mentioned is necessary. A common stearine candle or a lard oil lamp furnishes the best flame for use of the blowpipe ; the flame of a coal oil lamp should not be used.

2696. Zinc White (oxide of zinc)

2696.    Zinc White (oxide of zinc) is a permanent pigment; is not affected by sulphuretted hydrogen; does not form soap with oils and fats, therefore it retains its opacity; does not decompose other pigments, and if used with proper vehicles retains its whiteness. It is the best and safest white that can be used. It is most durable in silicious painting, as it forms chemical compounds with potash and silica.

2697. Sulphate of Baryta

2697.    Sulphate of Baryta, called bary-tes and constant white, is very permanent, of a bluish tint; has no body in oil, but is a good white in fresco, silicious, and water-color painting. Chemically it has no action on other colors, and is not itself affected by any ordinary destructive agent. It is a natural product, called heavy spar.

2698. Pfundheller's Method of Obtaining Barytes White

2698.    Pfundheller's Method of Obtaining Barytes White. Tor each 100 pounds of wool, 3 pounds alum, 1 pound cream of tartar, and 2 pounds sulphuric acid are to be combined with 1/8 ounce of soluble iodine violet, and the wool immersed in the solution at a temperature of 122° Fahr., and stirred round for an hour at this temperature. Another bath is to bo made in the meantime, in a fresh kettle, with 3 pounds chloride of barium, and the whole immersed in this, and kept at a temperature of 122° Fahr., for two hours. By this process the sulphate of barytes, the most beautiful of whites, will bo thrown down in the fibre of the wool, which has been saturated in the first bath with the sulphuric acid, and it will gain about eighteen per cent, in weight.