| By Weight. | By Volume. | Sp. gr. at 60° Fahr. | |
| Bulk before admixture. | Bulk after admixture and condensation. | ||
| Alcohol. Water. | Alcohol. Water. | ||
| 100·00 + 103·08 | 100·00 + 81·80 | 175·23 | ·91984 |
| 49·24 + 50·76 | 57·06 + 46·68 | 100·00 | |
The standard alcohol of the Revenue authorities, and that on which Gilpin’s Tables are founded, is a spirit of the sp. gr. ·825 at 60° Fahr., which is said to contain, by weight, 89% of pure alcohol of ·796; and 92·6% of alcohol, by volume, which corresponds to about 62·5 o. p.
It is of great importance to the spirit dealer to be able to estimate correctly the number of ‘proof gallons’ in any quantity of his commodities, or in the whole or any portion of his stock, as disagreeable errors frequently result from ignorance on this point. Calculations of this kind are extremely simple. Thus, when we find, by the hydrometer, that a given sample of spirit is 10 per cent. over-proof, it means, that 100 gallons of such spirit contain as much alcohol as 110 gallons of proof spirit.
In over-proof spirit, the per-centage o. p. always represents the quantity of water which the given spirit requires to reduce it to proof. By adding this per-centage over-proof to 100, we obtain a number which, multiplied by any number of gallons, and divided by 100, gives the exact number of proof gallons which is contained in any quantity of the spirit referred to. Thus:—A puncheon of rum gauged at 91 galls., and shown by the hydrometer to be 21 o. p., contains—
| 21 o. p. of sample added to 100 | 121 |
| No. of gallons of rum | 91 |
| ——— | |
| 11011 |
No. of gal. of proof-spirit = 11011 / 100 = 110·11
In like manner when a spirit is said to be 11 u. p., or under-proof, it means that 100 gal. of such spirit contains 11 gal. of water, and 89 gal. of ‘proof spirit.’ By deducting the per-centage under-proof from 100, we not only obtain the number of proof gal. contained in 100 gal. of such spirit, but, as in the last case, a factor which multiplied by any number of gal., and divided by 100, gives the exact number of ‘proof gallons’ contained in any quantity of the given strength. Thus:—An ullage brandy piece containing 45 gal. of spirit at 10 u. p., would have the proof value of—
| Per cent. u. p. of sample 10, subtracted from 100 | 90 |
| No. of gall | 45 |
| ——— | |
| 4050 |
Quantity of proof spirit = 4050 / 100 = 40·50
Or exactly 401⁄2 gallons.