LITHIUM [symbol Li, atomic weight 7.00 (O = 16)], an alkali metal, discovered in 1817 by J. A. Arfvedson (Ann. chim. phys. 10, p. 82). It is only found in combination, and is a constituent of the minerals petalite, triphyline, spodumene and lepidolite or lithia mica. It occurs in small quantities in sea, river and spring water, and is also widely but very sparingly distributed throughout the vegetable kingdom. It may be obtained (in the form of its chloride) by fusing lepidolite with a mixture of barium carbonate and sulphate, and potassium sulphate (L. Troost, Comptes rendus, 1856, 43, p. 921). The fused mass separates into two layers, the upper of which contains a mixture of potassium and lithium sulphates; this is lixiviated with water and converted into the mixed chlorides by adding barium chloride, the solution evaporated and the lithium chloride extracted by a mixture of dry alcohol and ether. The metal may be obtained by heating dry lithium hydroxide with magnesium (H. N. Warren, Chem. News, 1896, 74, p. 6). L. Kahlenberg (Jour. phys. Chem., 3, p. 601) obtained it by electrolysing the chloride in pyridine solution, a carbon anode and an iron or platinum cathode being used. O. Ruff and O. Johannsen (Zeit. elektrochem., 1906, 55, p. 537) electrolyse a mixture of bromide and chloride which melts at 520°. It is a soft, silvery-white metal, which readily tarnishes on exposure. Its specific gravity is 0.59, and it melts at 180° C. It burns on ignition in air, and when strongly heated in an atmosphere of nitrogen it forms lithium nitride, Li3N. It decomposes water at ordinary temperature, liberating hydrogen and forming lithium hydroxide.
Lithium hydride, LiH, obtained by heating the metal in a current of hydrogen at a red heat, or by heating the metal with ethylene to 700° C. (M. Guntz, Comptes rendus, 1896, 122, p. 244; 123, p. 1273), is a white solid which inflames when heated in chlorine. With alcohol it forms lithium ethylate, LiOC2H5, with liberation of hydrogen. Lithium oxide, Li2O, is obtained by burning the metal in oxygen, or by ignition of the nitrate. It is a white powder which readily dissolves in water to form the hydroxide, LiOH, which is also obtained by boiling the carbonate with milk of lime. It forms a white caustic mass, resembling sodium hydroxide in appearance. It absorbs carbon dioxide, but is not deliquescent. Lithium chloride LiCl, prepared by heating the metal in chlorine, or by dissolving the oxide or carbonate in hydrochloric acid, is exceedingly deliquescent, melts below a red heat, and is very soluble in alcohol. Lithium carbonate, Li2CO3, obtained as a white amorphous precipitate by adding sodium carbonate to a solution of lithium chloride, is sparingly soluble in water. Lithium phosphate, Li3PO4, obtained by the addition of sodium phosphate to a soluble lithium salt in the presence of sodium hydroxide, is almost insoluble in water. Lithium ammonium, LiNH3, is obtained by passing ammonia gas over lithium, the product being heated to 70° C. in order to expel any excess of ammonia. It turns brown-red on exposure to air, and is inflammable. It is decomposed by water evolving hydrogen, and when heated in vacuo at 50°-60° C. it gives lithium and ammonia. With ammonia solution it gives hydrogen and lithiamide, LiNH2 (H. Moissan, ibid., 1898, 127, p. 685). Lithium carbide, Li2C2, obtained by heating lithium carbonate and carbon in the electric furnace, forms a transparent crystalline mass of specific gravity 1.65, and is readily decomposed by cold water giving acetylene (H. Moissan, ibid., 1896, 122, p. 362).
Lithium is detected by the faint yellow line of wave-length 6104, and the bright red line of wave-length 6708, shown in its flame spectrum. It may be distinguished from sodium and potassium by the sparing solubility of its carbonate and phosphate. The atomic weight of lithium was determined by J. S. Stas from the analysis of the chloride, and also by conversion of the chloride into the nitrate, the value obtained being 7.03 (O = 16).
The preparations of lithium used in medicine are: Lithii Carbonis, dose 2 to 5 grs.; Lithii Citras, dose 5 to 10 grs.; and Lithii Citras effervescens, a mixture of citric acid, lithium citrate, tartaric acid and sodium bicarbonate, dose 60 to 120 grs. Lithium salts render the urine alkaline and are in virtue of their action diuretic. They are much prescribed for acute or chronic gout, and as a solvent to uric acid calculi or gravel, but their action as a solvent of uric acid has been certainly overrated, as it has been shown that the addition of medicinal doses of lithium to the blood serum does not increase the solubility of uric acid in it. In concentrated or large doses lithium salts cause vomiting and diarrhoea, due to a gastro-enteritis set up by their action. In medicinal use they should therefore be always freely diluted.
LITHOGRAPHY (Gr. λίθος, a stone, and γράφειν, to write), the process of drawing or laying down a design or transfer, on a specially prepared stone or other suitable surface, in such a way that impressions may be taken therefrom. The principle on which lithography is based is the antagonism of grease and water. A chemically pure surface having been secured on some substance that has an equal affinity for both grease and water, in a method hereafter to be described, the parts intended to print are covered with an unctuous composition and the rest of the surface is moistened, so that when a greasy roller is applied, the portion that is wet resists the grease and that in which an affinity for grease has been set up readily accepts it; and from the surface thus treated it will be seen that it is an easy thing to secure an impression on paper or other material by applying suitable pressure.
The inventor of lithography was Alois Senefelder (1771-1834); and it is remarkable what a grip he at once seemed to get of his invention, for whereas the invention of printing seems almost a matter of evolution, lithography seems to come upon the scene fully equipped for the battle of life, so that it would be a bold craftsman at the present day who would affirm that he knew more of the principles underlying his trade than Senefelder (q.v.) did within thirty years of its invention. Of course practice has led to dexterity, and the great volume of trade has induced many mechanical improvements and facilities, but the principles have not been taken any further, while some valuable methods have been allowed to fall into desuetude and would well repay some experimentally disposed person to revive.
Lithography may be divided into two main branches—that which is drawn with a greasy crayon (rather illogically called “chalk”) on a grained stone, and that which is drawn in “ink” on a polished stone. Whatever may be thought in regard to the original work of the artists of various countries who have used lithography as a means of expression, there can be little doubt that in the former method the English professed lithographer has always held the pre-eminence, while French, German and American artists have surpassed them in the latter.
Chalk lithography subdivides itself into work in which the black predominates, although it may be supported by 5 or 6 shades of modified colour—this branch is known as “black and tint” work—and that in which the black is only used locally like any other colour. Frequently this latter class of work will require a dozen or more colours, while some of the finest examples have had some twenty to thirty stones employed in them. Work of this description is known as chromo-lithography. Each colour requires a separate stone, and work of the highest quality may want two or three blues with yellows, reds, greys and browns in proportion, if it is desired to secure a result that is an approximate rendering of the original painting or drawing. The question may perhaps be asked: “If the well-known three-colour process” (see [Process]) “can give the full result of the artist’s palette, why should it take so many more colours in lithography to secure the same result?” The answer is that the stone practically gives but three gradations—the solid, the half tint and the quarter tint, so that the combination of three very carefully prepared stones will give a very limited number of combinations, while a moderate estimate of the shades on a toned block would be six; so that a very simple mathematical problem will show the far greater number of combinations that the three blocks will give. Beyond this, the chromo-lithographer has to exercise very great powers of colour analysis; but the human mind is quite unable to settle offhand the exact proportion of red, blue and yellow necessary to produce some particular class say of grey, and this the camera with the aid of colour filters does with almost perfect precision.