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 value. | Term. | Definition. |
|---|---|---|
| 0 | None. | No odor perceptible. |
| 1 | Very faint. | An odor that would not be detected ordinarily by the average consumer, but that could be detected in the laboratory by an experienced observer. |
| 2 | Faint. | An odor that the consumer might detect if his attention were called to it, but that would not attract attention otherwise. |
| 3 | Distinct. | An odor that would be detected readily and that might cause the water to be regarded with disfavor. |
| 4 | Decided. | An odor that would force itself upon the attention and that might make the water unpalatable. |
| 5 | Very strong. | An odor of such intensity that the water would be absolutely unfit to drink. (A term to be used only in extreme cases.) |
CHEMICAL EXAMINATION.
EXPRESSION OF RESULTS.
The results of chemical analyses shall be expressed in parts per million, which in most analyses is practically equivalent to milligrams per liter. In some laboratories other forms of expression have been used. Results expressed in parts per 100,000 or in grains per gallon may be transformed to parts per million, or conversely, by the use of the following table:
| Table 4.—Factors for transforming results of analyses. | ||||
|---|---|---|---|---|
| Unit. | Equivalent. | |||
| Grains per U.S. gallon. | Grains per Imperial gallon. | Parts per 100,000. | Parts per million. | |
| 1 grain per U. S. gallon | 1.000 | 1.20 | 1.71 | 17.1 |
| 1 grain per Imperial gallon | .835 | 1.00 | 1.43 | 14.3 |
| 1 part per 100,000 | .585 | .70 | 1.00 | 10.0 |
| 1 part per million | .058 | .07 | .10 | 1.0 |
The following general rules shall govern the use of significant figures in the expression of results:
1. If the results show quantities greater than 10 parts per million use no decimals; record only whole numbers. If the quantities reach hundreds and thousands of parts record only two significant figures.