Pure sulphate of manganese 1 part, pure acetate of manganese 1 part, calcined sulphate of zinc 1 part, white oxide of zinc 97 parts. The sulphate and acetate are ground in a mortar to an impalpable powder, which is passed through a metallic sieve. Three parts of this powder are dusted over the 97 parts of oxide of zinc, spread over a board or a slab; the whole is then thoroughly mixed and ground. The resulting white and impalpable powder, mixed in the proportion of 1/2 to 1 per cent with zinc white, will enormously increase the drying property of this product, which will become dry in from ten to twelve hours.

Volatile Oils, procured by distillation from turpentine and other vegetable substances, are almost destitute of the strength of the expressed oils, having hardly more cementing power in painting than water alone, and are principally used as solvents, and media of resinous and other substances introduced into vehicles and other varnishes. In drying they partly evaporate and partly, by combination with oxygen, form resin and become fixed. They are not, however, liable to change color like expressed oils of a drying nature, and, owing to their extreme fluidness, are useful diluents of the latter; they have also a bleaching quality, whereby they in some degree correct the tendency of drying and expressed oils to discolorment. Of the essential oils, the most volatile and nearest in this respect to alcohol is oil of sassafras, but that most used in painting is the rectified oil, improperly called spirits of turpentine, preferable only on account of its being thinner and more free from resin. By the action of oxygen upon it, water is either generated or set free, and the oil becomes thickened, but is again rendered liquid by a boiling heat upon water, in which the oxygen and resin are separated from it.

When colored by heat or otherwise, oil of turpentine may be bleached by agitating some lime powder in it, which will carry down the color. The great use of this oil, under the name of turps, is to thin oil paints, and, in the larger use thereof, to flatten white and other colors, and to remove superfluous color in graining. It, however, weakens paint in preventing its bearing out, and when used entirely alone, it will not fix the paint.

The name of turpentine is applied to a liquid, or soft solid product of certain coniferous trees, and of the Pis-tachia terebinthus.

There are several varieties, as follows: American or white turpentine, Bordeaux turpentine, Venice turpentine, Strasburg turpentine, Canadian turpentine, or Canadian balsam, Ohio turpentine and Frankincense.

In nearly all cases the processes of collecting are similar. A hollow is cut in the tree yielding turpentine, a few inches from the ground, and the bark removed for the space of about 18 inches above it. The turpentine trickles down into vessels placed to receive it. The incisions are made about the close of March, and the turpentine continues to run throughout the vegetative season, especially during the summer months. In general character these turpentines have much in common; they are oleo-resins, varying slightly in color, consistency and smell; they enter into the composition of many varnishes.

Oil of turpentine is obtained by distilling American terpentine, which has been melted and strained with water in an ordinary copper still. The distilled product is colorless, limpid, very fluid and possessed of a very peculiar smell.

The residuum, after the distillation of the oil or spirits of turpentine, is the common resin of trade.