Fig. 124. Distilling Apparatus.
One hundred cubic centimeters of the liquor are placed in a flask of from 250 to 300 cubic centimeters capacity, fifty cubic centimeters of water added, the flask attached to a vertical condenser by means of a bent bulb tube, 100 cubic centimeters distilled and the specific gravity of the distillate determined. The distillate is also weighed, or its weight calculated from the specific gravity. The corresponding percentage of alcohol by weight is obtained from the appended table, and this figure multiplied by the weight of the distillate, and the result divided by the weight of the sample, gives the per cent of alcohol by weight contained therein.
The percentage of alcohol by volume of the liquor is the same as that of the distillate, and is obtained directly from the appended table.
In distilled liquors about thirty grams are diluted to 150 cubic centimeters, 100 cubic centimeters distilled and the per cent of alcohol by weight determined as above.
The percentage of alcohol by volume in the distillate is obtained from the appended table. This figure divided by the number expressing the volume in cubic centimeters of the liquor taken for the determination (calculated from the specific gravity), and the result multiplied by 100 gives the per cent of alcohol by volume in the original liquor.
618. Determining the Specific Gravity of the Distillate.—The specific gravity of the distillate may be determined by the pyknometer, alcoholometer, hydrostatic balance or in any accurate way. The volume of the distillate is not always large enough to be conveniently used with an alcoholometer, especially the large ones employed by the Bureau of Internal Revenue. In the laboratory of the Agricultural Department, it is customary to determine the density of the distillate by the hydrostatic balance shown in paragraph [285]. The specific gravity is in each case determined at 15°.6, referred to water of the same temperature, or if at a different temperature calculated thereto.
619. Table for Use with Hydrostatic Plummet.—It is more convenient to determine the density of the alcoholic distillate at room temperature than to reduce it to the standard for which the plummet is graduated. In the case of a plummet which displaces exactly five grams, or multiple thereof, of distilled water at 15°.6, the corrections for temperatures between 12°.2 and 30° are found in the following table, prepared by Bigelow.[635]
If the weight of the alcoholic solution displaced be 4.96075 grams the apparent specific gravity 0.99215 and the temperature of observation 25°.4, the correction, which is additive, as given in the table is 0.00191 and the true specific gravity is 0.99406 and the percentage of alcohol by volume 4.08.
When the plummet does not exactly displace five grams of water at 15°.6, but nearly so, the table may still be used.
For example, suppose the weight of water displaced be 4.9868 instead of five grams. The apparent specific gravity of the water by this plummet is 0.99736 and the difference between this and the true specific gravity is 0.00264, which is a constant correction to be added to the specific gravity as determined in each case.