XITHIUM. 332 LITHOGRAPHY. suflBcient quantities of sodium bicarbonate and lithium caibouate. The salicylutc of lithium, LiCjHjOa. is a white powder readily soluble in water and in alcohol; it may be prepared by heat- ing lithium carbonate with salicylic acid and water, until effervescence ceases. A number of lithium salts are used in gout, in uric acid giarel, and calculus, owing to their capacity for causing sodium urate to dissolve in water. The carbon- ate, in the form of a lotion, is used to alleviate the pain of gouty iullaiiiuiation and to heal gouty ulcers. The presence of lithium compounds in a given substance can be readily recognized by in- troducing a small amount of the substance into a colorless flame (like that of the iJunsen burn- er), to which they impart a characteristic red coloration. lilTHODOMUS, LiTHOPHAGUS. See Mussel. LITHOGENESIS. The branch of geologic science which deals with the origin of rocks. As to the nature of the rock masses which consti- tuted the crust of the earth upon its primary cooling, little is known, nor is it certain that they are represented in any of the formations of the present day. From a studj' of the rock- forming processes now going on, and of the character of those masses that are exposed at the earth's surface, geologists have groui)ed all rocks upon a genetic basis, into three great classes or divisions. (1) The metamorphic rocks include those that have been profoundly changed from their original condition. The oldest rocks of which we have knowledge — the gneisses and crystalline schists — are members of this class ; they are characterized by a banded or foliated structure, and m.iy have originated from either sedimentary or igneous rocks by the effects of heat and pressure. (2) The igneous rocks com- prise those which have cooled from a molten con- dition, such as lavas and granites. They have a massive structure and a glassy or crystalline texture. (.S) The sedimentary rocks include those which have been derived from the igneous or metamorphic rocks by disintegration and de- cay, and which have been laid down on water or land. The water-deposited or aqueous rocks are the most important of this class; they are largely composed of fragmentary materials arranged into layers or strata, and hence are knov'n also as sedimentary rocks. See Rocks. LITHOGRAPHIC STONE (from Ok. XWos, lithos, stone -f- -ypaipuv, iinipheln, to write). An even-grained, compact limestone, generally of a gray, drab, or yellowish color, that finds exten- sive use in litho<;raphy. LITHOGRAPHY. Properly speaking, the art of writing, drawing, or engraving on stone of a particular kind, or on metals endowed with simi- lar qualities; in a more general sense, the art of chemical or surface printing from stone or metal. by means of which drawings or writing traced with fatty ink are multiplied, in contradistinc- tion to letter-press or relief, and copperplate or intaglio printing. This art or process is based purely upon the principle of chemical affinity of fatty or resinous matter for substances of the same nature and their repugnance for water. The stone or metal used is. by reason of its porosity, capable of re- ceiving and retaining water to the evaporating point, as well as fatty or resinous matter, to such an extent that to remove it mechanical means or powerful chemical agents are necessary. Pkocesses a^d ilATEBiALS. When a drawing is made on stone or metal with either litho- graphic crayon or ink and all other parts of the surface are moistened with water, both the fatty substance and the moisture will penetrate the porous surface. A roller covered with fatty or resinous printing-ink passed over this stone or metal will cause the ink to adhere to the fatty or resinous parts constituting the design, and will be- repelled b}- the moist parts; in consequence, the former only will appear in an impression. The stone used in lithography is a variety of calcium carbonate of porous texture, known as 'lithographic stone.' The best variety is found at Solenhofen, Bavaria, and almost the entire industry receives its suppl}- from that source. Stone of an inferior quality is quarried in Eng- land, France, Italy, Prussia, and Russia, and in later years in Canada and some of the Western States. Lithographic stone varies in color from a blue gray to a yellowish gray, the best quality being found among the light gray, and sometimes among the dark yellow varieties. The dark blue- gray or French stone is very fine in texture, but its color does not contrast sutliciently with that of the design to enable the artist or transferer to judge his work as well as on the light gray stone. It is sawn at the quarries into slabs from three to four inches in thickness, varying in size from 6X8 inches to 44 X 64 inches, and sold at prices ranging from lli^ cents to .30 cents per pound, according to size and quality. The larger sizes are extremely scarce when without flaws, such as open veins, streaks of glass, or soft lime spots. It is partly due to this fact, and partly to the greater expense attached to the handling of stone, that almost since the invention of lithog- raphy a substitute has been sought for it. Zinc has been used during the last seventy years or more, in its natural state as well as. later on, with a coating embodying the components of the lithographic stone, under the name of 'ealc- sinter' plates. The use of zinc plates as a sub- stitute for stone is, however, confined to the more ordinary grades of work, owing to the inferior and uncertain results obtained. About 1890 John Mullaly experimented with aluminum as a substitute for lithographic stone. His experi- ments were finally crowned with success, but it was some time before lithographers could be per- suaded to make use of it. In the year 1804 Dr. Otto Strecker, of Mainz, Germany, invented a method now called the 'Strecker process.' for treating aluminum plates with a coating of alu- minum salt. This method has come into very general use in Germany, and similar processes are now very considerably used in England. Ger- many. France. Russia, the United States, and other countries. Aluminum plates are said to have advantages over stone as to quality of work, and, apart from that, to offer all the advantages re- sulting from their uniform quality, their econ- omy, flexibility, exemption from breaking, and ease of handling and storage. Designs can be removed from either stones or plates by chemical or mechanical means and their surfaces prepared for the reception of new designs about 200 times in the case of a stone four inches thick and of an aluminum plate 29-1000 of an inch thick. Lithographic crayon is composed of beeswax.
