Its most important use is in the preparation of oil paints and varnishes. By painters both raw and boiled oil are used, the latter forming the principal medium in oil painting, and also serving separately as the basis of all oil varnishes. Boiled oil is prepared in a variety of ways—that most common being by heating the raw oil in an iron or copper boiler, which, to allow for frothing, must only be about three-fourths filled. The boiler is heated by a furnace, and the oil is brought gradually to the point of ebullition, at which it is maintained for two hours, during which time moisture is driven off, and the scum and froth which accumulate on the surface are ladled out. Then by slow degrees a proportion of “dryers” is added—usually equal weights of litharge and minium being used to the extent of 3% of the charge of oil; and with these a small proportion of umber is generally thrown in. After the addition of the dryers the boiling is continued two or three hours; the fire is then suddenly withdrawn, and the oil is left covered up in the boiler for ten hours or more. Before sending out, it is usually stored in settling tanks for a few weeks, during which time the uncombined dryers settle at the bottom as “foots.” Besides the dryers already mentioned, lead acetate, manganese borate, manganese dioxide, zinc sulphate and other bodies are used.
Linseed oil is also the principal ingredient in printing and lithographic inks. The oil for ink-making is prepared by heating it in an iron pot up to the point where it either takes fire spontaneously or can be ignited with any flaming substance. After the oil has been allowed to burn for some time according to the consistence of the varnish desired, the pot is covered over, and the product when cooled forms a viscid tenacious substance which in its most concentrated form may be drawn into threads. By boiling this varnish with dilute nitric acid vapours of acrolein are given off, and the substance gradually becomes a solid non-adhesive mass the same as the ultimate oxidation product of both raw and boiled oil.
Linseed oil is subject to various falsifications, chiefly through the addition of cotton-seed, niger-seed and hemp-seed oils; and rosin oil and mineral oils also are not infrequently added. Except by smell, by change of specific gravity, and by deterioration of drying properties, these adulterations are difficult to detect.
LINSTOCK (adapted from the Dutch lontstok, i.e. “matchstick,” from lont, a match, stok, a stick; the word is sometimes erroneously spelled “lintstock” from a supposed derivation from “lint” in the sense of tinder), a kind of torch made of a stout stick a yard in length, with a fork at one end to hold a lighted match, and a point at the other to stick in the ground. “Linstocks” were used for discharging cannon in the early days of artillery.
LINT (in M. Eng. linnet, probably through Fr. linette, from lin, the flax-plant; cf. “line”), properly the flax-plant, now only in Scots dialect; hence the application of such expressions as “lint-haired,” “lint white locks” to flaxen hair. It is also the term applied to the flax when prepared for spinning, and to the waste material left over which was used for tinder. “Lint” is still the name given to a specially prepared material for dressing wounds, made soft and fluffy by scraping or ravelling linen cloth.
LINTEL (O. Fr. lintel, mod. linteau, from Late Lat. limitellum, limes, boundary, confused in sense with limen, threshold; the Latin name is supercilium, Ital. soprasogli, and Ger. Sturz), in architecture, a horizontal piece of stone or timber over a doorway or opening, provided to carry the superstructure. In order to relieve the lintel from too great a pressure a “discharging arch” is generally built over it.