Alcoholmetry. The percentage of absolute alcohol in any spirituous liquid may be given either by volume or weight, but as liquors are sold by measure, not weight, it is generally preferred to know the percentage by volume. The per cent, of weight remains the same in all temperatures, but the per cent. by volume varies with the temperature or heat of the liquid. Many instruments have been introduced to determine the quantity of absolute alcohol contained in any spirituous liquors, and these are known as hydrometers, or alco-holmeters. Hydrometers made by different inventors have come into use in different countries; thus the hydrometer made by Tralles has been adopted by the governments of the United States and Prussia; that made by Gay Lussac has been legally sanctioned in France and Sweden; while that invented by Sikes has been approved and made the excise standard in Great Britain.

54. Tralles'Hydrometer

54. Tralles'Hydrometer. Tralles' hydrometer is the instrument used by our government to ascertain the strength of imported liquors, and is made of glass. Tralles has adopted as the standard of comparison pure or absolute alcohol in volume at the temperature of 60° Fah., the strength of which he expresses by a scale divided into 100 degrees or parts, each of which represents 1/100 part of alcohol. When floated in any spirituous liquor at a temperature of 60° Fah., it immediately indicates the strength. For instance, if in a brandy at that temperature it sinks to 65, it shows that 65 parts of the liquor is absolute alcohol, and 35 parts water; should it sink to 90, it indicates that the liquor is 90 parts or per cent, strong, and so on.

An increase of heat causes liquids to expand in volume, and a decrease produces contraction ; therefore spirits over the normal temperature of 60° Fah. appear stronger than they really are, and below 60° they are really stronger than they appear to be.

It is therefore evident that the degrees of percentage of this hydrometer are only correct when the spirit under trial has the normal temperature of 60° Fah. When the temperature varies from 60°, the percentage can only be ascertained by a long and tedious calculation. To avoid this Mr. Tralles has constructed a simple table by which the real percentage of alcohol is found in liquids of different temperatures from the results exhibited by the instrument. (See No. 55 (Table to find the true percentage of Absolute Alcohol).) The horizontal line at the top shows the various temperatures given by the thermometer; the column of figures under 60° shows the true percentage of strength at the normal or standard temperature of 60°; the figures under the other degrees of temperature show the observed or apparent degrees of strength as indicated by the hydrometers.

As an example of the simple manner by which this table may be used, we will suppose that the temperature of the spirits to be tested is at 75°, Fah., and that the hydrometer sinks to 53° on the scale; this would be the observed or apparent degree or percentage of strength. Now to find the real percentage of strength at 60°, we turn to the table and find the upright or vertical column of figures headed 75°, we then run down the figures until we arrive at 53.0; having ascertained this, we then trace the horizontal line to the left or right to the outside column headed 60°, and at the point when the horizontal line running from 53.0 meets the column headed 60°, will be found the number 50. We thus ascertain that a spirit at 75° having an observed strength of 53 has only a real percentage of 50 at the normal or established temperature of G0°. Suppose that another sample of brandy, instead of being at 75° is at 50°, and the instrument still sinks to 53. In the same way we select the column headed 50°, and run down the figures until we find 53.0, then by tracing the horizontal line until we arrive at the outside column headed 60° (either the first or last column), we find the number 55, which is the true percentage of the brandy at 60° Fah.

Again, if an alcoholic liquid at a temperature of 30° be found to contain 23.5 per cent, by volume, by reference to the table 30 will be found to express its actual strength at 60° Pah.

We might multiply examples, but the above are sufficient to show the manner by which the table may be worked.