LEAFLETS 8 and 9 of “Methods for the Detection of Toxic Gases in Industry”, published by the Department of Scientific and Industrial Research (H.M. Stationery Office, 2s. 6d. each net) deal with phosgene and arsine, respectively. The methods used are colorimetric, the reagents being diphenyl-amine and p-dimethylaminobenzaldehyde in the case of phosgene, and mercuric chloride in the case of arsine. Full directions for performing the tests are given.