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LEAD PLASTER

A mixture of lead soaps of fatty acids, prepared by heating olive oil with litharge or by heating a solution of lead nitrate vith sod;um linoleate; used in medical practice as an external application and as a drier in varnishmaking.

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LINSEED OIL

is expressed by pressure from flax seed, and is largely used in making paints, varnishes, linoleum, patentleather lacquers, rubber substitutes, and soft soaps, while the residual cake is used for feeding cattle. The cake is known to contain hydrocyanic acid derived from a contained glucoside, but most of it is dissipated during the maceration of the seeds and by evaporation. Linseed oil has a sp. gr. of o932 to 0938, a saponification value of 185 to 195, and iodine value 171 to 200. It contains linoleic acid is said to accompany the linoleic acid as a constituent of the oil. A published description of linseed oil is to the effect that it consists of 85 to 90 per cent, liquid glyoer ides, containing about 5 per cent, oleic acid, 15 per cent, linoiic acid, 15 per cent, linolenic acid, and 65 per cent, isolinolenic acid, the remaining 10 to 15 per cent, being made up of glycerides of solid fatty acids, chieily paln itic. When first expressed, the oil is pale yellow and not dis agreeable in smell, but unless it is reiined it quickly turns rancid, dark in colour, and repulsive in odour. It is soluble in alcohol, chloroform, carbon disulphide, benzol, and turpentine. Heating alone, under pressure, at a constant temperature greatly increases the viscosity and the iodine value decreases, while the saponification value remains unchanged. When boiled until it loses oneeighth of its weight, it thickens, becomes viscid, and dries quickly upon exposure to air. The oxidation of linseed oil by a current of aii is facilitated by the use of a little manganese dioxide or other drier, and this process gives “body” and drying properties to the product. Saponified with alkalies, linseed oil gives soft soap of a thin character. Supplies come front many places, and Argentine has about 3,500,000 acres of flax under cultivation. Linseed yields bj pressure aided with heat, about 27 per cent, of linseed oil.

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LUTECIUM

Atomic weight, J75. One of the extremely rare, recently discovered elements of the yttrium group.

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LITHOPONE

A white paint pigment having zinc sulphide, zinc oxide, and barium sulphate as chief basic constituents, prepared by strongly heating a mixture of zinc sulphide and barium sulphate, or one of barium sulphide and xinc sulphate, to redness.

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LUBRICANTS

Preparations used to decrease the friction between opposed solid faces, which auses, as is supposed by some, from true cohesion. The solid varieties include natural and artificial graphite, talc, mica, and other substances, such as flowers of sulphur” and whitelead, which are used for curing hot bearings. The natural graphite is usually of the socalled flake variety, and varies in size of particles from in. and less than in., whilst the artificially produced kind is amorphous, and ground even finer tbai; the natural product. The latter is sold under the trade names of “Aquadag” anil “Hydrosol” when in admixture with water, and as “Oildag,” “Oleosol,” and “Kollag” when in admixture with oil. Generally speaking, solid lubricants are applied dry in cases where for special reasons it is inadvisable or not possible to use liquid or semisolid lubricants, although they are usually employed in admixture with oil or as ingredients in greases. “Aquadag” used as a cylinder lubricant has been found advantageous where solid friction occurs, as in wormgear, although equally good results have been obtained by the use of natural flake graphite; and it has been concluded that the lubricating value of graphite depends upon its chemical purity. The lubricating value of oil depends upon somethin? not yet properly understood; it is not viscosity. What, however, is required in a liquid lubricant is that it shall penetrate into the narrow spaces between journal and bearing, thus “wetting” or spreading over the surfaces which are in motion together. The function of a lubricant is to keep metal surfaces separate with a minimum expenditure of energy, Vegetable and animal oils possess greater value than mineral oils obtained from crude petroleum and coal tar, which are also used as lubricants in common with the so called rosin oil, obtained by the destructive distillation of resin. They are generally graded in accordance with their specific gravities and viscosities. The socalled “germ process” of lubrication employs one or more fatty acids with mineral oil as the instrument of lubrication, i or 2 per cent, being incorporated according to chemical circumstances. This is said to reduce the coefficient of friction from 00084 to 00052that is, some 25 per cent, on a frictiontesting machine. Oils exhibit a rapid increase in viscosity with pressure, this increase being much greater for the mineral than for animal and vegetable oils.

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LYE

A solution of alkali such as used in soapmakIng.

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LEUCO BASES

Colourless compounds produced by reduction of dyes which are reconverted by oxidation into lyes.

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LATENT HEAT

is the heat absorbed in a state of physical change, such as that of solid ice to liquid water. This particular change renders latent that amount of heat which would serve to raise the temperature oi the same weight of water through 79 degrees C.

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LITMUS SOLUTION

may be used for the same purposes as litmus paper.

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LEUCINE

A decomposition product of albuminoid bodies generally accompanying tyrosine in the animal economy.

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