Ebullioscopes

EBULLIOSCOPES. This name encompasses two groups of instruments with different purposes: 1) instruments used to determine the molecular weight of soluble bodies by determining the rise in the boiling point of a solvent resulting from the introduction of said bodies; these include, for example, the Beckmann apparatus (see Beckmann apparatus), Landsberger's apparatus, and others. The determination principle is based on the fact that a relationship exists between the molecular weight of the soluble body and the rise in the boiling point of the solvent: M = E ^m/_t, where M is the molecular weight of the dissolved body, m is the number of grams of the dissolved body per 100 g of solvent, t is the rise in the boiling point of the solvent, and E is a constant value for each solvent (e.g., for water = 5.2). 2) Instruments used to determine the amount of alcohol in wine; the determination principle is based on the following: pure alcohol boils at 78.4°, and distilled water at 100°. Mixtures of alcohol and water have intermediate boiling points that are lower the higher the alcohol content. In addition to alcohol and water, the boiling point of wine is influenced by extractive substances of the wine, such as salts, sugars, and others; therefore, the determination of alcohol in wine by means of ebullioscopes is not among the most accurate methods. A number of instruments have been proposed for this purpose (Salleron, Malligand, Amagat, and others); the Salleron ebullioscope has gained the widest distribution, consisting of reservoir A (see figure), a condenser EFl₁, and thermometer T. The reservoir, surrounded by a tube CD that prevents its cooling, terminates in a horizontal tube with a stopcock R at the end. This tube is heated by a burner L. Performance of the determination: 50 cm³ of water is poured into reservoir A and, after heating to a boil, the temperature (t₁) is noted. Then the scale of the ruler attached to the instrument is set so that the observed temperature (t₁) coincides with zero on the ruler. Next, instead of water, 50 cm³ of wine is poured into the reservoir, brought to a boil, and the temperature (t₂) is noted. Leaving the ruler in its previous position, one looks at what number on the ruler corresponds to the movable scale; this will be the strength of wine expressed in volume percentages. The duration of the determination is 15–20 minutes. When determining alcohol in table wines containing no more than 10% of it, the error does not exceed 0.1%; for stronger wines, as well as sweet and extractive wines (see Wine), it is necessary to dilute the wine 2–3 times or more with multiplication of the obtained result by the dilution coefficient; the error in these cases rarely exceeds 0.2–0.3%.