[15] This number is obtained thus:—
| 100 /·79381 = 12·6 (nearly), |
| 12·6 × 175·25 = 2207·7. |
100 - 12 = 88% of proof spirit;
and—
2207·7 / 88 = 25·1 gal. (nearly).
That is, 251⁄10 gal. of such spirit would contain 100 lbs. of absolute alcohol.
By removing the decimal point one place to the right, we have the equiv. measure of 1000 lbs. By removing it one, two, or three places to the left, we have it respectively for 10 lbs., 1 lb., and 1⁄10 lb.; from which the equiv. for all other weights may be easily obtained.
By reversing the above operation, the measure of alcohol corresponding to any given weight of spirit, at any strength, may also be easily found.
The weight of 1 gal. of absolute alcohol being 7·938 lbs.; that of 1 gal. of proof spirit, 9·2 lbs,; and that of the ‘alcohol’ in 1 gal. of proof spirit, 4·53 lbs.; the weight of any number of gallons or volumes of either, and their equivalents, may be easily found. Thus:—
| gallons of alc. × 7·938 | = | lbs. weight of alc. |
| gallons pf. sp. × 9·2 | = | lbs. w. of pf. spt. |