HYDROMEL. Syn. Hydromeli, L. An aqueous solution of honey. Prep. (P. Cod.) Honey, 2 oz.; boiling water, 32 oz.; dissolve, and strain. A refreshing and slightly laxative drink; in fevers, hoarseness, sore throats, &c.
HYDROM′ETER. Syn. Areometer, Gravimeter; Hydrometrum, L. An instrument for ascertaining the specific gravities of liquids, and hence their strength, the latter being either in inverse or direct proportion to the former. Hydrometers are of two kinds:—1. Those which are always immersed to the same depth in distilled water, and the liquid to be tried, small weights being used for the purpose, as in Fahrenheit’s and Nicholson’s hydrometers; and 2nd, those which are suffered to rise or sink freely in the liquid, until they come to a state of rest, as in Syke’s, Baumé’s, &c. In both cases a correction must be made for any variation in temperature.
Of the two kinds, the first give the most accurate results, and have the great advantage of being applicable to liquids either lighter or heavier than water, but the second are the readier in practice, requiring less time and less skill to use them. The following are those best known:—
Baumé’s hydrometer or AREOMETER, which is very generally employed on the Continent, consists of two distinct instruments, the one for liquids heavier than water, the other for liquids lighter than that fluid. The first floats at the 0, or ‘zero,’ of the scale, in distilled wafer, at the temperature of 58° Fahr., and each degree, marked downwards, indicates a density corresponding to one per cent. of common salt. The hydrometer for liquids lighter than water is poised so that the 0 of the scale is at the bottom of the stem, when it is floating in a solution of 1 oz. of common salt in 9 oz. of water, and the depth to which it sinks in distilled water shows 10°; the space between these fixed points being equally divided, and the graduation continued upwards to the top of the scale.
The temperature at which these instruments were originally adjusted by Baumé was 12·5° Centigrade (54·5° Fahr.). They are now commonly adjusted in this country at 58° or 60° Fahr. Hence arise the discrepancies observable in the published tables of the “correspondence between degrees of Baumé and real specific gravities.”
Cartier’s hydrometer, which is much used in France for light liquids, has the same point for the zero of its scale as Baumé’s, but its degrees are rather smaller, 30° Baumé being equal to 32° Cartier.
Fahrenheit’s hydrometer consists of a hollow ball, with a counterpoise below, and a very slender stem above, terminating in a small dish. The middle, or half-length of the stem, is distinguished by a fine line across it. In this instrument every division of the stem is rejected, and it is immersed in all experiments to the middle of the stem, by placing proper weights in the little dish above. Then, as the part immersed is constantly of the same magnitude, and the whole weight of the hydrometer is known, this last weight, added to the weights in the dish, will be equal to the weight of fluid displaced by the instrument, as all writers on hydrostatics prove. And accordingly, the specific gravities for the common form of the tables will be had by the proportion—
As the whole weight of the hydrometer and its load, when adjusted in distilled water, is to the number 1000, so is the whole weight when adjusted in any other fluid, to the number expressing its specific gravity.
Gay-Lussac’s alcoholometer is used to determine the strength of spirituous liquors. It, at once, indicates on the stem, the per-centage of absolute alcohol in the liquid examined. The original experiments of Gay-Lussac having been made on liquids at a temperature of 59° Fahr., all examples examined by the alcoholometer, must either be brought to that temperature previous to being tested, or a correction made in the strength found.
Nicholson’s hydrometer is constructed on the same principle as Fahrenheit’s. It has in addition to the small dish for weights above, a little cup attached below, for holding any solid body whose weight in water is required. It is chiefly intended for taking the sp. gr. of minerals.