Chlorine also forms chlorinated organic compounds by action on the organic matter present in water and some of the objectionable tastes and odours of chlorinated waters have been attributed to this agency. Some observers have stated that chloramines were amongst the chloro-organo compounds produced but the author's experience with the Ottawa supply has demonstrated that simple chloramine (NH_{2}Cl) can be successfully employed for water treatment without causing complaints. It was suggested on page 28 that some of the higher chloro-amines might be the cause of some complaints but at present there is no definite information regarding the formation of these compounds in water and all such hypotheses are little more than conjectures. Letton[1] has reported that at Trenton, in 1911, when the water of the Delaware River was first treated, the dosage was as high as 1.2 p.p.m. of available chlorine and although chemical tests showed the absence of free chlorine, the water had an extremely disagreeable taste which was especially noticeable in the hot water. The conclusion was reached that "the taste and odour were not those of chlorine, but were due to some complex chemical change brought about by the action of the chlorine on the organic matter present in the water." The waters that require the most accurate adjustment of chlorine dosage, if complaints are to be avoided, are those containing very small amounts of organic matter. The margin between the dosage required for the attainment of a satisfactory degree of bacteriological purity and that which may cause complaints is usually very small, often less than 25 per cent, with the waters of the Great Lakes and many filter effluents. On the other hand, coloured waters containing large amounts of organic matter can be treated with an excess of chlorine without causing tastes and odours. The author found that the addition of 1.5 p.p.m. of available chlorine to the Ottawa River water did not cause complaints although only 0.8 to 0.9 p.p.m. were usually required for satisfactory purification. Harrington of Montreal has had a similar experience with this water. The presence of traces of foreign substances in water sometimes produces chlorinated derivatives having repugnant tastes and odours. Creosote and tar oils have caused an odour somewhat resembling that of iodoform and industrial wastes have also produced complaints. The substitution of chlorine gas (liquid chlorine) for bleach solutions has apparently eliminated tastes and odours in some cases but this may be due to a more perfect control over the dosage rather than to any property of the bleach _per se_.