The stones are prepared for lithography by polishing in the ordinary way; the style of work for which they are intended determining the degree of labour bestowed upon them.
For crayon drawings the surface should have a fine grain, but the finish of the stone must depend upon the desired softness of the intended drawing; for writing or drawing on in ink the surface must receive a higher polish, and must be finished off with pumice-stone and water.
The best lithographic stones are obtained from Solenhofen, near Munich, and from Pappenheim, on the banks of the Danube. The white lias which lies immediately under the blue, near Bath, also yields good lithographic stones, and furnishes the principal portion of those employed in this country. See Crayons, Ink and Paper.
LITHONTRYP′TICS. Syn. Lithotryptics, Lithontryptica, L. Under this head are intended numerous substances (LITHICS; LITHICA, L.) used to prevent the formation of urinary calculi, or to dissolve them when already formed. Those employed with the former intention are more correctly termed ANTILITHICS (ANTILITHICA, L.), and those with the latter, LITHONTRYPTICS, or LYTHONLYTICS (LITHONTRYPTICA, LITHONLYTICA, L.).
The following are the principal substances included under this head by pharmacological writers:—Alkalies and their carbonates, benzoic acid, borax, carbonate of lithia, effervescing solution of lithia, carbonic acid, cinnamic acid, diluents (generally), diuretics (generally), juniper, malic acid, Malvern waters, mineral acids, nitrosaccharate of lead, opium, phosphate of soda, phosphoric acid, poppies, turpentines, uva ursi, vegetable acids, vegetable astringents, vegetable bitters, Vichy waters, wall pellitory, water (pure).
LIT′MUS. Syn. Turnsole; Lacmus, Lacca cærulea, L. musiva, L. musci, L. A blue substance prepared by the united influence of water, air, ammonia, and either potassa or soda, from Rocella tinctoria, Lecanora tartarea, or any of the other tinctorial lichens capable of yielding archil, by a process essentially similar to that adopted for the latter substance, except that chalk is generally used to form the paste, which is moulded into cakes and dried.
Pur., &c. “Soluble in both water and alcohol. Its blue colour is reddened by acids, and is restored by the addition of alkalies.” (Ph. L. 1836.) It is extensively used by the dyer as a red and crimson colouring matter, and by the chemist as a test for acids.
The colouring matter of litmus, when purified as much as possible, may be kept for an indefinite period unaltered in glycerin. Litmus is treated with hot water, and the solution, after concentration, is mixed with a sufficient quantity of alcohol (of 80 per cent.) to precipitate the colouring matter. After standing for twenty hours the alcohol is poured off, and carries with it a dirty blue foreign substance, which frequently occurs in litmus, and is not altered by acids. The sediment is treated with hot water, which dissolves it on account of the potassium carbonate which is present.
To remove this carbonate, sulphuric acid is added till the liquid assumes a faint wine tint; it is then heated to boiling for a few minutes, and again rendered blue by the addition of a few drops of lime water. After the lapse of twenty-four hours the liquid is filtered, and evaporated to a syrup, and left all night in a cool place, when the potassium sulphate crystallises out in the form of a crust. It is then filtered through a moist cotton mixed with glycerin, and carefully preserved from damp.[22] See Archil, Cudbear, &c.
[22] J. C. Martenson, from ‘Chem. Centr.,’ translated into the ‘Journal of the Chemical Society.’