Caseine le also made on a commercial scale, aud seems to be used in some of the foreign boot and leather varnishes. Legumine, which might easily be obtained in large quantities from any oheap beans, tares, or other leguminous seeds, has never been used to any important extent in water-varnishes.
(4) Gum arable and the allied acacia g-ums (p. 1630) are not so much used pure in glazes and varnishes as gelatine, but enter into and give gloss to many liquid preparations, such as blacking, ink, boot-glosses and varnishes, kid-revivers, &e., and form the vehicle or cementing material for artists' water-colours.
5. Lac, dissolved in water by means of borax or alkaline carbonates, also makes a good water varnish, and the solution forms the principal ingredient in many of the beat boot- and leather varnishes, and in waterproof inks.
Volatile solvents.—Turpe (essential oil or spirit of turpentine,* pp. 1431, l686) is the volatile oil, obtained by distillation from the turpentines of the coniferous trees, of which it constitutes 10-35 per cent. It is at the present day found very pure in commerce, being at a low price; but when the price becomes high, adulteration with petroleum and rosin-spirit is much practised.
Turps is the most important solvent used in varnishes of the third and fourth divisions, and every care should be taken to choose it of the best quality, i. e. free from adulteration, and new, or freshly-distilled. Old turps should never be used, especially if it shows the least thickening or " fatness," for although such " fat " turps unquestionably helps oil-varnishes to dry quickly (owing to the oxygen it has absorbed from the air, and holds in very loose combination), and is therefore, and for the brilliancy it gives them, sometirnes preferred by varnish-makers of the old school, yet it only does so at great cost of hardness and durability.
Turps is also the solvent chiefly used in varnishes belonging to Class A of the fourth division, and here it is especially desirable that it should be new, or the varnish may remain for days before it is dry enough to be touched with safety, catching dust all the time.
Petroleum, Benzoline, Benzine-spirit, Gazoline, &c. (pp. 1433,1509)4 The different substances composing the liquid called " naphtha," vary in composition (and in sp. gr. and boding-point) frorn marsh-gas, the first of the series (CHO up to the solid paraffins. The oils boiling below 180° (356° F.) may as solvents be conveniently divided into four portions :—(1) Those boiling below 70°
(158° F.), (2) between 70° and 100° (158°-212° F.), (3) between 100° and 130° (212°-266° F.), and (4) between 130° and 160° (266°-320° F.). No. 1 may be sometimes used with advantage to replace ether and benzol economically, in varnishes belonging to Class B of Div. IV. intended to dry instantly ; No. 2 may replace in Classes B, C, and D, of Div. IV., alcohol in some cases, and benzol and toluol in others; No. 3 evaporates much more quickly than turps, though not so quickly as alcohol, and rnay therefore be used where an essence-varnish is required to dry rather quickly, or to increase the solvent power of alcohol ; and No. 4 is in many cases in Class D of Div. IV. an important substitute for turps, when it is particularly desirable to prepare an oil- or essence varnish absolutely free from contamination by the resins always contained in turps, or which are sure to be formed in it, after it (or any varnish containing it) has been kept a few weeks.
The petroleum-oils, though rather inferior to turps in solvent power for some resins, have over it an immense advantage, in their very great stability, and resistance to the action of oxygen. They keep good for years, even in the light, without ever " fattening," and may be distilled over and over again to dryness without leaving any appreciable residue in the retort.
Shale-oils (pp. 1433, 1510).—These differ from petroleum, inter aim, in containing amongst their lighter oils bodies belonging to the ethylene series, whose general formula is C„ H2„ . In general characters and solvent powers, they would seem to be almost identical with petroleum.
Rosin-spirit (p. 1681) is the lighter portion of the oils (" rosin-oil") produced by the destructive distillation of common rosin at nearly a red heat. Rosin-spirit begins to boil at about 110° (230° F.), but rapidly rises to 130° (266° F.), between which point and 240° (464° F.), the greater part distils over. It has no fixed boiling-point, being a mixture of hydrocarbons even more cornplex than coal-naphtha or petroleurn. Its odour, which in the crude product is like wood-tar, but far stronger, becomes much milder and less disagreeable after refining. It is an excellent solvent, rnuch resembling turps, than which, after refining, it is much less oxidizable.