The supply of purified poisonous tar having been exhausted in the preceding experiments, further study of the active principle is postponed until more can be prepared. It is highly desirable to investigate the white precipitate formed by addition of sulphuric acid to an alcoholic solution of the toxicodendrin. OXIDATION OF THE PURIFIED TAR WITH NITRIC ACID. When the purified poisonous material (p. 32) was extracted with 50 per cent. alcohol, only a small quantity was dissolved as was stated above. The insoluble residue was treated with fuming nitric acid. Violent reaction took place at once with copious evolution of red fumes and heat. When the reaction was over, a sticky red gummy mass was left which was slightly soluble in cold water and readily soluble in warm alcohol. The water extract was yellow, and the alcoholic solution was red. That the water extract contained picric acid was shown by the following experiments: (1) A portion was gently warmed with a few drops of a strong solution of potassium cyanide and two drops of sodium hydroxide. The red color of potassium isopurpurate was formed. (2) A portion of the water solution was heated with glucose and a few drops of sodium hydroxide. The deep red color of picraminic acid was produced. (3) A few drops of an ammoniacal solution of copper sulphate was added to the water extract. A yellow-green precipitate was formed. (4) The water extract dyed silk, but did not dye cotton cloth. DISTILLATION OF THE TAR WITH SODA LIME. About 25 gm. of the tar left after extracting the original material with hot water was dissolved in ether and poured into a glass retort containing soda lime. The ether was distilled out, leaving the tar intimately mixed with the soda lime. The retort was then gradually heated. Vapors and liquid were given off, both of which turned red litmus blue and had a strong odor like tobacco smoke. No odor of ammonia was detected.[45] At the high temperature of the triple burner, a semi-solid, red, greasy substance collected in and closed the condenser tube. This substance had the same powerful odor as the liquid portion of the distillate. The clear, watery portion of the distillate was separated from the thicker parts, and was found to contain pyrrol and pyridine derivatives by the following characteristic tests: (1) Wood moistened with hydrochloric acid was turned red by it. (2) Colorless fumes were formed when brought near hydrochloric acid; mixed with hydrochloric acid, a red insoluble substance was formed. (3) It precipitated the hydroxides of iron, gave a light blue precipitate with copper sulphate, and a white precipitate with mercuric chloride.