acid groups. In the presence of this sulfonated colloid comprising 50% by weight of the 0.40-ml. aqueous sample, 0.004 gram of sulfuric acid was precipitated quantitatively.The following acids at the concentration shown have also been found to form precipitates of their aniline salts when 0.40 ml. of their aqueous solution is added to 25 ml. of aniline: sulfurous (saturated), phosphoric (1 M), oxalic (0.5 M), and tartaric (0.5 M). The residual solubilities of these acids in aniline have not been studied. The following acids gave no trace of precipitate when added to aniline in this same proportion: hypochlorous (saturated), hydrochloric (0.5 to 5 M), perchloric (0.5 M), hydrobromic (0.5 M), hydrosulfuric (saturated), nitric (0.5 to 5 M), boric (saturated), arsenious (saturated), acetic (0.5 M), trichloroacetic (0.5 M), benzoic (saturated), malonic (0.5 M), fumaric (saturated), succinic (0.5 M), citric (0.5 M), o-phthalic (saturated), lactic (0.5 M), salicylic (saturated), and aspartic (satu-rated). Monobasic amino acids such as glutamic (saturated), alanine (0.5 M), methionine (saturated), and glycine (0.5 M) are precipitated, probably as the zwitter-ions rather than as the aniline salts.When inorganic cations (as sodium, potassium, and ammonium) are present along with sulfate ions they are quantitatively precipitated from aniline as the inorganic sulfates. It is not unlikely that the inorganic sulfates could be separated on the filter from aniline sulfate, as by ether washing, and separately accounted for.Satisfactory aniline can be prepared by distilling wet technical grade aniline. The water is first carried over in a milky emulsion, after which the clear dry aniline distills over. In this way it is very easy repeatedly to recover satisfactory aniline for re-use.