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. ODOR.[4][14][53][72][92][114][115][121c] 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: COLD ODOR. Shake the sample violently in one of the collecting bottles, when it is half to two-thirds full and when the sample is at room temperature (about 20° C.). Remove the stopper and smell the odor at the mouth of the bottle. HOT ODOR. Pour about 150 cc. of the sample into a 500 cc. Erlenmeyer flask. Cover the flask with a well-fitting watch glass. Heat the water almost to boiling on a hot plate. Remove the flask from the plate and allow it to cool not more than five minutes. Then agitate it with a rotary movement, slip the watch glass to one side, and smell the odor. EXPRESSION OF RESULTS. Express the quality of the odor by a descriptive epithet like the following, which may be abbreviated in the record: a—aromatic C—free chlorine d—disagreeable e—earthy f—fishy g—grassy m—moldy M—musty P—peaty s—sweetish S—hydrogen sulfide v—vegetable. Express the intensity of the odor by a numeral prefixed to the term expressing quality, which may be defined as follows: Numerical Term. Definition. value. 0 None. No odor perceptible. 1 Very An odor that would not be detected ordinarily by faint. the average consumer, but that could be detected in the laboratory by an experienced observer.