In the classification of this science, it has been divided into inorganic chemistry, relating to metals, minerals and bodies not associated with organic life, and organic chemistry, which was formerly limited to matter associated with or the result of growth or life processes, but which is now extended to the broader field of all carbon compounds. In later years the most remarkable advances have been made in the field of organic chemistry. The four elements carbon, hydrogen, oxygen and nitrogen have been juggled into innumerable associations, and in various proportions, and endless permutations, have been combined to produce an unlimited series of useful compounds, such as dyes, explosives, medicines, perfumes, flavoring extracts, disinfectants, etc. The most interesting of these compounds are the _coal tar products_. Coal tar, for many years, was the waste product of gas making. Forty years ago about the only use made of it was by the farmer, who painted the ends of his fence posts with it to prevent decay, or by the fisherman, who applied it to the bottoms of his boats and his fishing nets. To-day the black, offensive and unpromising substance, with magical metamorphosis, has been transformed by the chemist into the most beautiful dyes, excelling the hues and shades of the rainbow, the most delightful perfumes and flavoring extracts, the most useful medicines, the most powerful antiseptics, and a product which is the very sweetest substance known. The aniline dyes represent one of the great developments in this field. In 1826 Unverdorben obtained from indigo a substance which he called “Crystalline.” In 1834 Runge obtained from coal tar “Kyanol.” In 1840 Fritzsch obtained from indigo a product which he called “Aniline,” from “Anil,” the Portuguese for indigo. Zinin soon after obtained “Benzidam.” All these substances were afterward proved to be the same as aniline. Perkins’ British patent, No. 1,984, of 1856, is the first patented disclosure of the aniline dyes, and represents the beginning of their commercial production. This combines sulphate of aniline and bichromate of potash to produce an exquisite lilac, or purple color. The first United States patent was in 1861, and now there are about 1,400 patents on carbon dyes and compounds, the most of which belong to the coal tar group. In dyes artificial alizarine, by Graebe and Lieberman (Pat. No. 95,465, Oct. 5, 1869); aniline black, by Lightfoot (Pat. No. 38,589, May 19, 1863); naphthazarin black, by Bohn (Pat. No. 379,150, March 6, 1888); artificial indigo, by Baeyer (Pat. No. 259,629, June 13, 1882); the azo-colors, by Roussin (Pat. No. 210,054, Nov. 19, 1878); and the processes for making colors on fibre, by Holliday (Pat. No. 241,661, May 17, 1881), are the most important. The artificial production of salicylic acid, by Kolbe (Pat. No. 150,867, May 12, 1874), marks an important step in antiseptics. Artificial vanilla, by Fritz Ach (Pat. No. 487,204, Nov. 29, 1892), represents