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An intratracheal instillation technique was developed which permits the repeated administrations of precise volumes of particulate suspension into mouse lungs. Benzo(a)pyrene (BP) adsorbed to ferric oxide was used to test the feasibility of the method. The majority of the animals survived 4 weekly treatments. Histological and fresh tissue sections showed extensive penetration of both chemicals into the lung parenchyma; however, while BP was eliminated from the organ rapidly, the ferric oxide was retained for over a 100 days. These dust particles were observed inside macrophages collected around terminal bronchioles and lymphoid tissues of the lungs.

NotesVol. 75 with methanol. The m.p. of this material, 16.3 g., was 67-72°( unsharp). Since repeated recrystallizations from methanol did not give a substance with sharp m.p., we dissolved the material in petroleum ether and chromatographed it on alumina, collecting fractions of 50 ml. Fractions 5-8 gave a crystalline residue of m.p. 86-87°, which upon recrystallization from isopropyl alcohol formed vellow cubes of m.p. 87°.

The only representative of the class of quinoxaline-2-thiols was recently reported by Wolf, Wilson, Jr., and Tishler.3 This paper presents the preparation of quinoxaline-2,3-dithiol, an unusually sensitive reagent for nickel. The dithiol was prepared by treating 2,3dichloroquinoxaline with thiourea and hydrolyzing the isothiouronium salt. This compound was also made by refluxing a mixture of 2,3-dihydroxyquinoxaline and phosphorus pentasulfide in dry pyridine.Also described is the preparation of 3-alkylquinoxaline-2-thiols. These compounds were prepared directly by treating the corresponding chloroquinoxalines with thiourea in absolute alcohol. The intermediate isothiouronium salts did not precipitate, and the desired thiols crystallized on cooling.All of these thiols were characterized by converting them to mercapto ethers. EXPERIMENTAL4Quinoxaline-2,8-dithiol. (a) From 2,3-dichloroquinoxaline. A solution of 4 g. (0.02 mole) of 2,3-dichloroquinoxaline5 and 8 g. (0.105 mole) of thiourea in 100 ml. of absolute alcohol was refluxed for two hours. The solution was concentrated to a small volume, diluted with 250 ml. of water, made alkaline by the addition of 25 g. sodium hydroxide, and then refluxed for one-half hour. On acidifying with acetic acid, a brownish-orange product formed which was separated by filtration, washed with water and dried. The yield -was 3.76 g. or 96.4%.The dithiol could not be recrystallized from any solvent tried, but was purified for analysis by repeated dissolving in alkali and reprecipitation by acetic acid. Prolonged heating in alkaline solution appeared to cause some oxidation and lightening of color. A characteristic behavior was shown on heating. Between 230-250°the color of the compound started to change to chrome yellow; the change wras completed by 280°. Decomposition began at 290-295°, with partial fusion, at which point the substance turned greenish-gray.

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