HYDRATES; are compounds of the oxides, salts, &c. with water in definite or equivalent proportions. Thus slaked lime consists of one atom of quick-lime = 28, + one atom of water = 9, of which the sum is 37 on the hydrogen scale.
HYDRAULIC PRESS. See [Oil], [Press], and [Stearine].
HYDRIODIC ACID; (Acide Hydriodique, Fr.; Hydriodsäure, Germ.) is an acid formed by the combination of 99·21 parts of iodine, and 0·79 hydrogen. When pure, it occurs in the gaseous state, but it combines with water like the hydrochloric or muriatic acid gas into a liquid acid.
HYDROCHLORIC ACID; the new chemical name of [muriatic acid], which see.
HYDROGEN; (Eng. and Fr.; Wasserstoff, Germ.) an undecompounded gaseous body; the lightest of all ponderable matter, whose examination belongs to chemistry.
HYDROMETER; an instrument for ascertaining the specific gravities of liquids. Baumé’s hydrometer, which is much used in France, and other countries of the continent of Europe, when plunged in pure water, at the temperature of 58° Fahr., marks 0 upon its scale; in a solution containing 15 per cent. of common salt, (chloride of sodium) and 85 of water by weight, it marks 15°; so that each degree is meant to indicate a density corresponding to one per cent. of that salt. See [Areometer], for comparative tables of hydrometers.
HYDROSULPHURETS; chemical compounds of bases with [sulphuretted hydrogen].
HYMENŒA COURBARIL; a tree growing in South America, from which the resin [animé] exudes.
HYOSCIAMUS NIGER. Henbane is a plant used in medicine, from which modern chemistry has extracted a new crystalline vegetable principle called hyosciamine, which is very poisonous, and when applied in solution to the eye, determines a remarkable dilatation of the pupil; as belladonna also does.
HYPOSULPHATES; Hyposulphites; saline compounds of the hyposulphuric or hyposulphurous acid with bases.