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Put′ty-pow′der.

An oxide of tin, or of tin and [1837] lead mixed in various proportions, used as polishing powder by opticians and lapidaries.

It is prepared by oxidizing the metal in a closed iron box having a perforation in front, which is surrounded by the fire and maintained at a red heat, the metal being constantly stirred to expose all portions of it to the air; when entirely oxidized it is removed from the box, the lumps of oxide are selected from the mass and ground, the powder being afterward sifted. The whitest powder, if heavy, is the purest. Inferior kinds are brown or yellow; others, having a small quantity of ivory-black intermixed, are known as gray putty. Pure white putty, used by marble-workers, opticians, etc., is the smoothest and most cutting: it should consist of oxide of lead alone; but to lessen the difficulty of manufacture, a little lead (the linings of tea-chests) or of an alloy called schruff (prepared by the pewterers) is added to assist oxidation.

Putty-powder of fair commercial quality is prepared from equal parts of tin and lead. A common dark-colored powder is prepared from lead alone, but is much inferior in quality.

Putty-powder for fine optical uses may be prepared by dissolving tin in nitro-muriatic acid, filtering the solution, and precipitating the peroxide thus formed with liquid ammonia; the precipitate is washed with water, collected on a cloth filter, dried and pressed so as to form a lump, which is broken into pieces and, after farther drying, levigated on a glass plate with an iron spatula, and subjected in a crucible to a low white heat. The powder is then washed or elutriated to remove the coarser particles. This process is due to Mr. Ross.

1877.

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Sir James Ross (1)
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