Pure acetic acid may be made by mixing dry acetate of potash with oil of vitriol in a retort, and distilling the acetic acid into a very cold receiver; this, when flavored with various volatile oils, forms the aromatic vinegar sold by druggists. It is a very strong acid, and if applied to the skin will quickly blister it.
VARNISHES.
Varnishes are solutions of various resinous substances that will dry with a bright surface on exposure to the air. They are used to protect different substances from the action of the atmosphere, and to give them an elegant bright surface; woods and painted work are the chief things varnished; metals are coated with a kind of varnish called “lacquer,” this is to prevent the bright surface of the metal from being dulled by the air or damp, and to give an artificial appearance to some metals; tin, for instance, if lacquered with yellow lacquer, acquires somewhat the appearance of brass. Mastic varnish is the varnish generally used for paper and pictures; it is made by dissolving gum mastic in oil of turpentine. Copal varnish is that most generally used for carriages and wood, it is made by adding boiled linseed oil to melted copal, and afterwards thinning it with oil of turpentine. A common varnish, fit for many purposes, may be made by adding common resin to oil of turpentine, and warming it till dissolved. Lacquers are made by dissolving shellac and various other gums in strong spirits of wine, and in some cases coloring it, either yellow, by means of gamboge, or red, by dragon’s blood (a kind of resin). French polish is nearly the same as lacquer, but the mode of applying it is different; the grain of the wood is first filled up by means of drying oil and chalk rubbed in, when this becomes thoroughly dry, a rubber of flannel is covered by a piece or two of clean old linen, and some of the polish put on it, just enough to moisten it, and then a little oil, this is slowly rubbed round and round, the varnish adhering to the wood, and the oil preventing the rubber sticking to it, and at the same time, polishing the surface of the varnish as it dries. This process requires a good deal of art to produce a perfect surface.Old work, before being varnished with any varnish that contains oil (as copal varnish), should be thoroughly freed from grease or greasy matter, or the varnish will never dry. Good varnish should dry in twenty-four hours so that dust will not adhere to it.
OILS.
PRESSING LINSEED FOR OIL.
Oils, whether animal or vegetable, have pretty much the same properties. The vegetable oils are got by crushing and pressing certain seeds, as linseed; the animal oils are obtained chiefly from the whale and seal tribe, or from fish, as the cod and sturgeon. They are viscid and of a pale yellow color, lighter than water, and therefore float upon it, and are very combustible. Oils are used for a multiplicity of purposes: for burning in lamps, for making paints and varnishes, preventing the friction of machinery, in making soap, and numerous other processes. Oils are generally divided into fixed and volatile oils; as an example of the first, linseed oil may be selected; of the last, oil of lavender.
Some of the fixed oils are called drying oils, and it is this kind that are used for varnish making; as linseed oil possesses the properties of this class very perfectly, it may serve as a description of all. Linseed oil has the power of drying when spread out in a thin layer, becoming of a resinous consistence like varnish, and upon this quality depends the drying powers of paint, for the other non-drying oils, as olive oil, may be exposed to the air for months without drying at all; the drying powers of linseed oil are greatly increased by boiling it with litharge (oxide of lead). This forms the drying or boiled oil used in painting, and is employed in making varnishes, printers’ ink, and for other purposes. Oiled silk is formed by brushing silk over with this oil and exposing it to the air till it is dry; this oiled silk is the same that is used for sponge-bags and bathing-caps. Of the non-drying oils, the chief are those used for burning in lamps, as sperm oil. Salad oil is expressed from the olive, and is called olive oil. Of the volatile oils, the most useful is oil of turpentine, commonly called spirit of turpentine; it is got by distilling common turpentine (the concrete juice of trees of the fir and pine tribe), it has a strong odour, is very inflammable, and is volatile, that is to say, if spread out, will evaporate, leaving nothing behind; this oil is capable of mixing with drying oils, and it not only increases their drying powers, but, by thinning them, makes them more applicable to many purposes. Oil of turpentine dissolves resin and many resinous substances, and forms useful varnishes with them. Mastic varnish is mastic dissolved in oil of turpentine; it is the varnish always used for varnishing pictures. Many of the volatile oils are used as perfumes, and the odour of plants and flowers depends upon the volatile oil which evaporates from them, as lavender, cloves, and others. Peppermint water, dill water, and cinnamon water are produced by distilling water mixed with the substances, and is simply water containing a small quantity of the volatile oil of these substances in solution; but eau-de-Cologne and lavender water, although called “waters,” are mixtures of volatile oils and spirit of wine, and contain no more water than is comprehended in the spirit used.