A method of determining small quantities of acetone, alcohol, and benzene present in air has been described by Elliott and Dalton.2 A measured volume of the air is aspirated through the undermentioned liquids, which absorb the respective vapours. An alkaline iodine solution is used for absorbing the acetone, and the excess of iodine titrated with standard thiosulphate. The alcohol vapours are oxidised to acetic acid by means of a dilute solution of chromic acid, excess of the latter being then titrated with iodide and thiosulphate. For absorbing the benzene vapour a mixture of strong sulphuric acid and fuming nitric acid is employed. With the benzene this yields dinitrobenzene, which can then be extracted with ether, and estimated by reduction with a known quantity of stannous chloride, the excess of the latter being titrated with solution of iodine.

1 J. Ind. Eng. Chem., 1916, 8, 240. 2 Analyst, 1919, 44, 132.