Strength of distillate = 74·6 u. p. = 25·4 per cent. proof spirit.
_b._ From the TEMPERATURE of the VAPOUR, as originally proposed by Gröning. The bulb of a thermometer is thrust through a cork into the head of the still, or other vessel employed, and the temperature of the vapour in which it is immersed being noted, is sought in the following table:--
TABLE III.--_Showing the Alcoholic Content, by_ VOLUME_, of Boiling Spirits, and of their Vapour, from the Temperature of the latter, as observed by a Thermometer._ By GRÖNING.
+---------------+-------------------+-------------------+----------------+-------------------+------------------+ |Temperature of | Alcoholic content | Alcoholic content | Temperature of | Alcoholic content | Alcoholic content| | the Vapour. | of the Distillate | of the Boiling | the Vapour. | of the Distillate | of the Boiling | | Fahr. | per cent. | Liquid per cent. | Fahr. | per cent. | Liquid per cent.| +---------------+-------------------+-------------------+----------------+-------------------+------------------+ | 170·0 | 93 | 92 | 189·8 | 71 | 20 | | 171·8 | 92 | 90 | 192·0 | 68 | 18 | | 172·0 | 91 | 85 | 194·0 | 66 | 15 | | 172·8 | 90-1/2 | 80 | 196·4 | 61 | 12 | | 174·0 | 90 | 75 | 198·6 | 55 | 10 | | 174·6 | 89 | 70 | 201·0 | 50 | 7 | | 176·0 | 87 | 65 | 203·0 | 42 | 5 | | 178·3 | 85 | 50 | 205·4 | 36 | 3 | | 180·8 | 82 | 40 | 207·7 | 28 | 2 | | 183·0 | 80 | 35 | 210·0 | 13 | 1 | | 185·0 | 78 | 30 | 212·0 | 0 | 0 | | 187·4 | 76 | 25 | | | | +---------------+-------------------+-------------------+----------------+-------------------+------------------+
This method is admirably adapted to the purposes of the distiller and rectifier, as it furnishes a ready means of approximately determining the strength of the spirit passing over, at every part of the process of distillation, as well as that of the wash left in the still.
_c._ From the BOILING POINT, as originally proposed by M. l'Abbé Brossard-Vidal. This method is founded on the fact, that the boiling points of mixtures of alcohol and water, unlike water alone, are scarcely disturbed by the addition of saline, saccharine, or extractive matter within certain limits. It hence offers a ready means of determining the proportion of alcohol present in spirits, wines, fermented liquors, &c., with sufficient accuracy for all ordinary purposes. In applying it, a thermometer, with a large bulb and a narrow bore, and a movable scale graduated from 180° to 212° Fahr., is usually employed. Before using it as an alcoholometer, it is set, with its bulb immersed, in a small metallic boiler (brass or copper) containing distilled water, which is then raised to the boiling-point, and the 212° of the scale accurately adjusted on a level with the surface of the mercury, should it vary from that point. This is necessary on account of variations of atmospheric pressure causing corresponding variations of the boiling-points of liquids. It is then ready for several hours' operations, and, generally, for an entire business day, without further adjustment. The little boiler is next filled with the liquor to be examined, and the lamp again lighted. The temperature as shown by the scale of the instrument at the commencement of full ebullition being ascertained, may be sought in one of the following _Tables_, against which the alcoholic content of the liquor will be found (nearly).