Alcoholometer

Alcoholometer, an instrument for determining the amount of ethyl alcohol (spirit) in aqueous solutions of it. The principle of the instrument is based on the difference in densities of alcohol and water. The specific gravity of aqueous solutions of alcohol fluctuates within the limits of 0.79425-1.0. The first attempt in compiling tables of specific gravity of alcoholic solutions belongs to the English researcher Gilpin (1790). Tralles, using the data of his compatriot, as well as on the basis of his own research, first proposed (1811) an instrument for the quantitative determination of alcohol, based on the measurement of specific gravity. Tralles' alcoholometer, which obtained wide distribution, represents a glass hydrometer of ordinary type, equipped with a thermometer and a scale with divisions showing directly the content of ethyl alcohol in volume percent at a temperature of 12 4/9° R = 60° F (Fahrenheit). This temperature was used by Gilpin in his investigations and was adopted by Tralles for his alcoholometer. At present, the alcoholometer of Tralles is, in terms of accuracy and portability, advantageously replaced by a metal alcoholometer adopted for official use by the Main Directorate of Weights and Measures of the USSR. ........ It belongs to the type of hydrometers with constant weight and consists of a copper-gilded ball A (see figure) with soldered to it similar rods B and C. On the upper rod are divisions from 0 to 10, each of which in turn is divided into 5 equal parts. The rod C at its end carries a weight q, due to which C, when immersed in a liquid, occupies a vertical position. To C are attached 10 weights n with numbers 0, 10, 20... 80, 90, which can be put on the lower rod through slots. The metal alcoholometer can be used either with one of the weights or without a weight, thanks to which it combines in itself eleven alcoholometers with constant weight. The determination of volume percent is performed as follows: in a wide glass cup, which is attached to the instrument, is poured a carefully mixed test liquid, into which the alcoholometer and thermometer are carefully immersed. The alcoholometer must float freely in the liquid, not touching either the walls of the instrument or the thermometer. The divisions are counted from bottom to top: if the alcoholometer sinks to the line 0, the corresponding reading number will be 6.4; when immersed to the line 0.6, etc. If the alcoholometer does not sink to the lower line 0, a weight is selected for which the level of the liquid would fall on one of the 10 divisions. At concentrations close to absolute alcohol and at a temperature above 30°, the alcoholometer taken without a weight may sink above the line 10; in such a case the liquid should be cooled. Having read the level of immersion of the alcoholometer by the meniscus, its index is determined, adhering to the following rule: if the alcoholometer was immersed without a weight or with a weight of 0, then 100 is added to the number read on the rod. If, on the other hand, for the determination one used any of the weights, then the number marked on it is added to the number read on the alcoholometer. For example: 1) the alcoholometer without a weight sank to the line 4.2, the alcoholometer reading will be 104.2; 2) the alcoholometer with a weight of 40, the level reading 6.8, index = 46.8; 3) the alcoholometer with a weight of 0, reading 3.2, index = 3.2. The indices obtained in this way do not directly indicate the concentration of alcohol; the latter is determined by Tralles' tables, in which next to the alcoholometer readings and the temperature are given volume percent of anhydrous ethyl alcohol (specific gravity 0.7946 at 60° F, or 12 4/9° R = 15 5/8° C). All alcoholometers are calculated for pure, free of any impurities aqueous solutions of alcohol. The presence of impurities, as occurs, for example, in wines, liqueurs, beer, etc., requires preliminary distillation of the alcohol and its determination in the obtained distillate. The study of alcoholic solutions, in particular their specific gravity, was also engaged in by Gay-Lussac, Brix, Richter, Mendeleev. The tables proposed by them differ either in the temperature at which the measurements were carried out, or in that some give the content of alcohol in volume, others in weight percent.