A protocol for the chemical fractionation of sediments and biological testing of these fractions has been developed. Fractions obtained were directly tested for toxicity by using both the Salmonella typhimurium test and the Panagrellus redivivus test. When applied to sediments from Tobin Lake, Saskatchewan, this method demonstrated that the major toxic constituents of the sediment were neutral compounds that eluate from Florisil columns by 1:1 hexane-dichloromethane. This most toxic fraction contained none of the priority toxic chemicals. These tests demonstrate agreement between the two biological assay systems.contaminated with a single chemical issuing from a single source. Rather, there is an extensive multiplicity of compounds and sources contaminating most aquatic systems.Any system in close proximity to human activity will contain literally thousands of contaminating chemicals and their byproducts. The major problem in such systems is to determine which specific components pose the greatest long-and short-term risks to biological systems, including man. The question of what chemicals are present is secondary; the primary objective is to establish which compounds in a particular system pose the greatest risk.

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CXXVIL-The Preparation of Gua.nidine by the Interaction of Dicyanodiarnide and Ammonium Thioc yanat e. By EMIL ALPHONSE WERNER and JAMES BELL. BY heating a mixture of dicyaaodiamide and ammonium chloride a t 195O folr ten minutes, Bamberger and Dieckmann (Ber., 1892, 25, 545) obtained diguanidei, C,H,N,. The yieild wa,s pooh, and Ostrogovich (Bul. Soc. qtainfe Bucaregti 1910, 19, 641), using ammonium iodidei in plaae oif the ohloride, under similar wnditiolns, obtained it much btter resulti. The reactioin has been represented thus: HN:c(NH,)*NH.CN + NR,*HX= * This fact is not referred to in the literature : if a gram or two of dioyanodiamide i8 heated to the melting point in a porcelain crucible and quickly covered with a glass bell-jar standing over a layer of water, the latter after a few momentswill be found t o give quite a copious yellow precipitate of silver cytmamide on addition of ammonio-silver nitrate solution. u u'