at the same time illustrative of the absurdly unscientific nature of many of our commercial units of measurement. Formerly, in England, a little pile of gunpowder was made and the 'spirit' to be tested was poured over this and lighted. If the burning alcohol, before going out, set fire to the powder it was said to be above proof; if it went out without igniting the powder, it was said to be below proof. Thus 'proof spirit' was defined as the most dilute alcohol which would set fire to gunpowder under these conditions. The ridiculous inaccuracy of such a test is sufficiently apparent. The British parliament and our congress both passed laws defining 'proof' in terms of specific gravity.[1] The alcohol which we buy for use in alcohol lamps or for
- ↑ "'Proof spirit'. . . was defined by act of Parliament to be such that at 51° F. (10° C.) thirteen volumes shall weigh the same as twelve volumes of distilled water. The 'proof spirit' so made will have a specific gravity of 0.91984 at 15.5° C. (60° F.) and contain, according to Townes, 49.24 per cent, by weight of alcohol and 50.76 per cent, of water. Spirits weaker than proof are described as U. P. (under proof), stronger than proof as 0. P. (over proof); thus a spirit of fifty U. P. means fifty water and fifty proof spirit, while fifty O. P. means that the alcohol is of such strength that to every one hundred of the spirit fifty of water would have to be added to reduce it to proof strength."—'Handbook of Industrial Organic Chemistry,' by S. P. Sadler, p. 217.
"Proof spirit is alcohol of such a strength that 13 gallons of the spirit have the same weight as 12 gallons of distilled water at 10° C. Proof spirit contains 49.24 per cent, of absolute alcohol by weight."—'Outlines of Industrial Chemistry,' Thorpe, p. 409.
In the Zeitschrift fur angewandte Chemie, Vol. I. (1888), p. 29, may be found tables for the conversion of per cents, over and per cents, under proof into per cent, of alcohol by volume. According to these, for instance,
1 per cent, over proof equals 57.8 per cent, alcohol by volume
70 per cent, over proof equals 97.3 per cent, alcohol by volumethat is, 100 per cent., or absolute alcohol, beyond which we can not go, corresponds to a little less than 75 over proof. According to these tables again,
1 per cent, under proof equals 56.6 per cent, alcohol by volume
70 per cent, under proof equals 17.2 per cent, alcohol by volumethat is, pure water, containing no alcohol, is 100 below proof. The above figures show 'proof spirit' as containing about 57.2 per cent, alcohol by volume.
The above definitions apply in England, but not in the United States. Section 3,249 of the Internal Revenue Laws in force January 1, 1900 (page 144) reads: "Proof spirit shall be held to be that alcoholic liquor which contains one half its volume of alcohol of a specific gravity of seven thousand nine hundred and thirty-nine ten thousandths (0.7939) at sixty degrees Fahrenheit."
The following dialogue appears in the hearings before the Committee on Ways and Means, February-March, 1906, on page 121:
Mr. Boutell: "In that connection will you kindly explain the use of the word 'proof' in connection with alcohol? Absolute alcohol would be what proof?"
Professor Wiley: "It would be 200. That is, a commercial gallon of pure alcohol would be 200 proof."
Mr. Boutell: "And a gallon of it on which a tax of a dollar and ten cents is levied is 100 proof?"
