Phenylacetylene has been prepared by the elimination of carbon dioxide from phenylpropiolic acid by means of phenol[1] or aniline[2] or by heating with barium hydroxide;[3] from styrene dibromide, by heating with potassium hydroxide in alcohol;[4] by heating b-bromo or chloro styrene with sodium ethylate or potassium hydroxide in alcohol;[5] by passing the vapors of a-dichloroethylbenzene over hot soda lime;[6] by the action of alcoholic potassium hydroxide on dibenzal-acetone tetra-bromide;[1b] by the action of aqueous potassium hydroxide on phenyl propargylaldehyde;[2b] by the action of molten potassium hydroxide on b-bromo-styrene.[3b] [1] Ber. 20, 3081 (1887). [2] Rec. trav. chim. 16, 157 (1896). [3] Arm. 221, 70 (1883). [4] Ann. 154, 155 (1870); 235, 13 (1886); Bull. soc. chim. 35, 55 (1881); (3) 25, 309 (1901). [5] Ann. 308, 265 (1899); 342, 220 (1905). [6] Jahresb. 1876, 308; Gazz. chim. ital. 22 (2), 67 (1892); Bull. soc. chim. (3) 25, 309 (1901). [1b] Ber. 39, 4146 (1900). [2b] Ber. 31, 1023 (1898). [3b] J. Am. Chem. Soc. 44, 425 (1922). XIX PHENYLHYDRAZINE C6H5NH2<.>HCl + NaNO2 + HCl--> C6H5N2Cl + NaCl + 2H2O C6H5N2Cl + 4H(Na2SO3)--> C6H5NHNH2<.>HCl Prepared by G. H. COLEMAN. Checked by J. B. CONANT and H. R. THOMPSON. 1. Procedure IN a 12-l. round-bottom flask, fitted with a mechanical stirrer, are placed 1045 cc. of concentrated commercial hydrochloric acid (sp. gr. 1.138). The flask is surrounded with a freezing mixture of ice and salt, and when the contents are at 0'0, stirring is started and 500 g. of cracked ice are added; then 372 g. of aniline, also cooled to 0'0, are run in during five minutes. The mixture is treated with 500 g. more of cracked ice, and a cold solution (0'0) of 290 g. of technical sodium nitrite dissolved in 600 cc. of water are allowed to run in slowly (twenty to thirty minutes) from a dropping funnel, the end of which is drawn to a small tip, and reaches nearly to the bottom of the flask. During this addition, the stirrer is operated rather vigorously, and the temperature is kept as near 0'0 as possible by the frequent addition of cracked ice (about 1 kg). In the meantime, a sodium sulfite solution is prepared by dissolving 890 g. of sodium hydroxide, of about 90 per cent purity, in about 1 l. of water and then diluting to 6 l. A few drops of phenolphthalein solution are added and sulfur dioxide passed in, first until an acid reaction is indicated and then for two or three minutes longer. During the addition of the sulfur dioxide, the solution is cooled with running water. On account of the strong alkaline solution, the original color produced by the phenolphthalein is very faint, but this slowly increases until it becomes deep just before the acid point is reached. It is best to remove a small sample of the liquid from time to time, dilute with three or four volumes of water and add a drop more of phenolphthalein.