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.
2. If the results are between 1 and 10 parts do not retain more than one decimal place.
3. If the results are between 0.1 and 1 part do not retain more than two decimal places.
4. Estimates of ammonia, albuminoid, and nitrite nitrogen alone justify the use of three decimals.
5. If the results of analyses are tabulated ciphers should not be added at the right of the decimal point to make the column uniform.