Seed-lac is the resin removed from the twigs, and washed with water to remove the lac dye or coloring mat ter. It is coarsely pounded.
Lump-lac is seed-lac melted into lumps.
Shell-lac (or shellac) is prepared from seed-lac by melting and strain ing through cotton.
Lac Resin.—The essential principle of shellac may be obtained pure by refining shellac, which for this pur pose is treated with cold alcohol, fil tered, and distilled. It is a brown, translucent, hard, and brittle resin, and is very valuable. Shellac may be dissolved in alcohol, dilute hydrochlor ic and acetic acids, sal ammoniac, and alkalies. One part of borax dissolved in boiling water will dissolve five times its weight of shellac, making a solu tion which is as useful for many pur poses as spirit varnish.
Shellac is much favored as a var nish, being harder than rosin and eas ily soluble in alcohol. It is also the principal ingredient of the best seal ing wax. It is used as a size and has valuable waterproofing qualities.
Mastic.—A valuable gum resin pro duced from certain trees and shrubs in Barbary, the Levant, and China. It is used as an ingredient in many varnishes. Used by itself it is trans parent, brilliant, tough, and delicate. It is also often employed in finishing maps and paintings, also in medicine, dentistry, and in mounting articles for the microscope. Mastic is used with other ingredients in varnish to impart a gloss.
Rosin or Colophony. — This sub stance is the residue obtained by dis tilling crude turpentine from pine trees, of which it comprises about 70 per cent to 90 per cent. It is largely manufactured together with oil of turpentine in North Carolina. In col or it ranges, according to its purity, from transparent or straw color to a brownish yellow. It can be dissolved in alcohol, ether, wood spirit, linseed oil, or turpentine, partly in petroleum but not In water. It can also be dis solved by nitric acid and alkalies. It is largely used in varnishes and cements, in calking ships, in the preparation of plaster and ointments, in soldering metals, in making yellow soaps, and otherwise. A common use is for covering the bows of violins.
Sandarac is produced from a small coniferous tree in Barbary. It oc curs in pale-yellow oblong grains or tears covered with a fine dust. It is transparent and brittle. It is used in pharmacy as an incense, and in varnishes, and also in powdered form it is rubbed on writing paper where erasures have been made in order to prevent the spread of ink. It is part
ly soluble in cold alcohol, and wholly in alcohol brought to the boiling point.
Gums.—Gums are substances which occur in plants and some animals, but which are neither oily nor resinous. They exude for the most part from various trees when the bark is cut. The principal gums are arabic, Sene gal, mesquite, tragacanth, Bassora. They are principally employed in the manufacture of mucilage, also in med icine, pharmacy, confectionery, calico printing in the preparation of the inks, and also for sizes.
Gums Arabic and Senegal.—These gums exude from various trees in Africa and Asia, and are sold under various trade terms denoting the localities from which they come.
Gnm Mesquite.—A substance sim ilar to gum arabic, but produced in plants growing in the dry regions of Mexico and adjacent parts of the United States. It differs from the other gums in the fact that its prin ciple is not precipitated by borax.
Gums arabic, Senegal, and mesquite are easily soluble in hot or cold water, forming mucilage. They can be sepa rated from water by the addition of alcohol or subacetate of lead. They are coagulated by borax, except gum mesquite.
Gums tragacanth and Bassora swell, but do not perfectly dissolve, in water. They can, however, be rubbed with water into a very adhesive paste, which is not, strictly speaking, a solution.
Asphalt.—Asphalt occurs in nature in veins, beds, and lakes, usually be neath the surface of the ground. In the island of Trinidad, Venezuela, occur lakes of asphalts about three miles in circumference. It is a dry solid with a glossy black surface eas ily melted and very inflammable. It can be dissolved in alcohol, linseed oil, turpentine, or ether, also in ben zol and bisulphide of carbon. With benzol it forms an intensely black solution called black varnish. It is used for varnish, insulation, water proofing cement, roofing, and paint ing.
Kinds of Varnish.—The character of varnish is largely affected by the substance in which it is dissolved. Thus we have fixed-oil varnishes in which the principal solvent is turpen tine; spirit varnishes or " lac varnish es," true solutions of resins in alco hol, wood spirit, acetone, benzine, etc.; volatile-oil varnishes, the principal solvents being oil of turpentine, and ether varnishes, being solutions of res in in ether. In addition to the above are various special varnishes of gutta percha, wax, and other substances.