The strength of absolute alcohol (sp. gr. ·7938) is estimated at 751⁄4% over-proof. It therefore contains 1751⁄4% of ‘proof spirit,’
whilst proof spirit (sp. gr. ·91984) contains 57·06% of ‘absolute alcohol,’ both being by measure or volume. Thus—
(meas. of alc. × 1751⁄4) / 100 = equiv. meas. of pf. spt.
And—
(meas. of pf. spt. × 57·06) / 100 = equiv. meas. of abs. alc.
From which we derive the ‘constant multipliers’ 1·7525 (or roughly 13⁄4), and ·5706, applicable to any number of volumes or gallons. For—
meas. of alc. × 1·7525 = equiv. meas. of pf. spt.
and—
meas. of pt. spt. × ·5706 = equiv. meas. of alc.
To ascertain what quantity of a spirit at any given strength is equiv. to or contains 100 lbs. of absolute alcohol, we have only to divide the constant number 2207·7 by the proof value per cent. of such spirit.[15] Thus—for a spirit 12 u. p.—this would be