The Determination of Formaldehyde in Air. G. Romyn and J. A. V o w thius. (BUZZ. SOC. Chim., 1903, xxix., 540-543.) -Nessler's reagent is rapidly reduced by formaldehyde with the formation of metallic mercury, as in the subjoined equation (cf. ANALYST, xxi., 98) : The precipitate, whose colour depends on the quantity of substances used, can be rapidly and completely oxidized by means of a solution of iodine in potassium iodide, followed by the addition of a small amount of hydrochloric acid.

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... amount of formaldehyde can thus be calculated from the quantity of free iodine found in the liquid after the oxidation. For the determination of formaldehyde in air, a slow current is passed through Nessler's reagent contained in a Pettenkofer's or Kyll's tube. The standard solution of iodine is then introduced, and the liquid shaken until the precipitate has dissolved, and then, after the addition of a few drops of dilute hydrochloric acid, titrated with gn thiosulphate solution. According to the equation, 30.16 milligrammes of formaldehyde react with 1 molecule of mercuric iodide, or the amount of Nessler's reagent produced by 271 milligrammes of mercuric chloride. About 5 C.C. of the reagent are required to oxidize 21 milligrammes of formaldehyde, corresponding with 13 C.C. of & thiosulphate solution. C. A. M. The Determination of Benzene in Illuminating Gas. L. 116. Dennis and J. G. O'Neill. (Journ. Amer. Chem. SOC., xxv., 503.)-The authors show that, contrary to the general supposition, absolute alcohol does not remove either ethylene or benzene completely from gas mixtures, but that an ammoniacal nickel solution completely removes benzene, whilst ethylene and other hydrocarbons remain entirely unabsorbed. The small quwtity of ammonia vapour given off by the nickel solution is removed by shaking the gas with dilute sulphuric acid. To prevent a rise in