1. _Colour, odour, and taste._--The colour is best determined by filling a glass cylinder, about 2 feet in height, with the sample, placing it upon a white surface and observing the tint produced; or, by the use of a coloured glass tube of the same length, which is provided with glass plates attached at each end, and is filled with the sample and viewed when held towards a sheet of white paper. As a rule, pure water exhibits a light-bluish tint, a yellowish hue being generally considered a suspicious indication; but it frequently occurs that a perfectly colourless water is bad, and one possessing a decided colour may prove to be at least, fair in quality. The odour of the sample is ascertained by placing a corked bottle, one-half filled with the water, in a warm place (at about 38°) for some time, and then shaking the bottle, withdrawing the stopper and immediately testing the odour. Pure water should be free from much perceptible odour of any kind, and more especially from one of a disagreeable nature. The same remark applies to the taste. Water should be practically tasteless, even when warmed. It frequently happens, however, that a water may be highly contaminated with deleterious organic impurities, and still remain devoid of any marked unpleasant taste. There are few simple tests of any value which will reveal at once the sanitary quality of drinking water. One, sometimes employed, is to fill a clean quart bottle about three-fourths full with the suspected sample, and dissolve in it a teaspoonful of fine granulated white sugar. The bottle is then corked and allowed to remain in a warm place for two days, when, in the presence of sewage contamination, it will become cloudy or milky.[119] According to Wanklyn and Chapman,[120] if a brownish colour or precipitate is produced upon the addition of 1·5 c.c. of Nessler’s reagent (see p. 208) to 100 c.c. of the water, it should be considered unfit for domestic use.