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The value of the readings of tint and shade by the Lovibond tintometer^[66][82][83] has not been commensurate with the labor involved, but it is necessary to make a record of the reflected tint and shade^[50] of some waters. The standard color disks used in teaching optics may be used for the purpose.

Procedure.—The white disk supports three movable standard color sectors, red, yellow, and blue, and one movable black sector. All are mounted on a device which can be revolved rapidly, blending the colors into a uniform tint or shade. A scale around the circumference of the disk is used to indicate the percentage of each color or white or black in the blend.

Place the sample in a battery jar on a white ground; adjust the sectors so that when blended the tint or shade will match the reflected tint or shade of the sample. Report the percentages of red, yellow blue, white, and black in the blended tint or shade.

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The observation of the odor, cold and hot, of samples of surface water is important as the odors are usually indicative of organic growths or sewage contamination or both. The odor of some ground waters is caused by the earthy constituents of the water-bearing strata. The odor of a contaminated well water is often contributory evidence of its pollution. A study of the organisms as directed under Microscopical Examination (p. 90) is a valuable adjunct to physical and chemical examination of water. Certain odors distinguish or identify certain organisms, as, for example, the “fishy” odor of Uroglena, the “aromatic” or “rose geranium” odor of Asterionella and the “pig pen” odor of Anabaena. Observe and record the odor, both at room temperature and at just below the boiling point, as follows: