Hydrogen

[Fr. hydrogène; Gr. hudor, water, and gennao, to generate.] ( Chem.) An elementary substance, first isolated as a constituent of water by Cavendish in 1766. It is a colorle , transparent, tastele , inodorous gas, which is doubtfully claimed to have been liquefied. Hydroge'nium, n. See HYDROGEN. It is almost insoluble in water, 100 volumes of that Hydrogenous, a. Composed of, or relating to, hy- fluid only absorbing two volumes of the gas. It is the lightest substance in nature, 100 cubic inches of it weighing only 214 grains. It was at one time doubted whether it existed in the uncombined state in nature; but the experiments of Bunsen prove that it is evolved, though in very variable proportions, by the solfaturas of Iceland. As a constituent of water, it is most exten- sively distributed throughout nature. It also exists ir combination with oxygen in most inflammable minerals. It is an important element in all organic substances and enters into the composition of most substances in daily use, whether drawn from the mineral, vegetable oranima kingdom. Having a very great attraction for oxygen and chlorine, when in the nascent condition, it is much, employed in the laboratory for deoxidizing or dechlor- inating purposes. It is prepared in a variety of ways, the most usual being by pouring dilute sulphuric acid on granulated zinc or iron clippings, when the follow- ing reaction takes place: Hydrographer, n. [Fr. hydrographe .] One who describes the sea or other waters; one who draws maps of the sea, lakes, or other waters. Hydrograph'ic, or Hydrograph'ical, a . [Fr. hydrograph i que .] Relating to hydrography, or to the description of the sea, sea-coast, isles, shoals, depth of water, ., or of a lake. Hydro graphically, adv . In an hydrographical Hydrography, n. [Gr. hudor , water, and graphō , to describe.] The description of the waters existing on the surface of the earth; particularly with reference to the bearings of the coast, the depth, currents, and other circumstances important or useful in navigation. H. implies the same thing with regard to the sea that geography implies with respect to the land. - Hydro- graphical Charts or Maps are projections of some parts of the ocean, in which the meridians, parallels, ., with the coasts, capes, rocks, shallows, ., are laid down for the use of navigators. Hydrohæmatite, n. ( Min .) A hydrated oxide of iron. Same as TURGITE, q. v. Hy'droid, a. (Zool.) Hydra-like. Hy'droidæ, n . pl . ( Zool .) An order of Acalephs, which, in the cla ification of Aga iz, includes the lowest aca- lephs, and embraces two more or le distinct forms, one of which, though having the structure of acalephs, re- minds us of Polyps ; and the other closely resembles the Medusæ proper . All the so-called hydroid polyps, and the naked-eyed medu e, belong to this order, which is divided into 8 sub-orders. Hydrolan'thanite, n. ( Min .) Same as LANTHA- NITE, q. v. Hydro lite, n. ( Min .) A name given by some to the mineral Gmelinite (q. v.), from its containing about 20 per cent. of water. Hydrologist, n. One skilled in hydrology. Hydrology, n. [Fr. hydro logie ; Gr. hudor , water, and logos , discourse, doctrine.) (Phys. Geog.) The doc- trine or science of water, its properties, phenomena, and laws. The principal part of the water on the globe occupies a large depre ion of the surface, and is de- nominated the OCEAN. Different parts of it are known as the PACIFIC, the ATLANTIC, the INDIAN, the ARCTIC, and the ANTARCTIC oceans. The rest of the surface rises above the level of the ocean, or if depre ed is occupied by waters that do not connect with the great body of the ocean. The form of the land, or, in other words, the form of the line of intersection of the surface of the ocean with the land, is extremely irregular, the water entering the land at numerous rece es, and the land projecting into the water by various promontories. The former are called INLAND SEAS, GULFS, or BAYS, according to the extent to which the water is land-locked. The waters reposing in hollows within the land are called LAKES; and the waters running along the surface to enter the ocean or the lakes, or be lost in plains, are called RIVERS. The rivers connect with each other, and form large and definite RIVER SYSTEMS, draining definite tracts of land. The grand phenomena of the ocean in- clude the regular TIDES and CURRENTS which affect it, the WINDS and STORMS which disturb it, its temperature, depth, and mineral contents. The phenomena of fresh water actually on the surface are quite distinct; and the phenomena of water in the atmosphere, including the falling and distribution of rain, belong to METEO- ROLOGY, another department of Physical Geography. Few things connected with the laws of matter and their vis i- ble results on the earth are more striking than those which belong to the circulation of water around and through the earth. The warm air that floats above the surface of the ocean is constantly raising vapor, with which the atmosphere is charged to the extent of at least four parts out of five, being ready to give it off at the slightest change of temperature. When the air in this state impinges upon land, it becomes either more heated, and therefore more absorbent (the additional supply being readily obtained), or chilled and le absorbent, and in a condition to deposit moisture as rain. Thus, on all high grounds, which are nece arily colder than the lowlands in the same latitude, and on all cooler lati- tudes to which clouds are drifted, there is occasional rain, often very heavy and continuous, over large tracts. The rain that thus falls is partly, no doubt, reabsorbed into the air, or is used in the production of vegetable and animal ti ue. A great part, however, runs along the earth's surface in streams and rivers, circulating at the surface visibly, and the rest enters the strata, pervades them, and pa es through them invisibly from place to place, coming out again in springs, and completing an- other circulation out of sight. The influence of water is felt everywhere; and all the phenomena of structure observable in rocks of every kind are influenced by this complete and never-ceasing circulation. H. is thus a department of great importance and interest. The de- tails will be found considered in various separate articles, of which the names are printed above in capital letters. Hydromagne's ite, n . ( Min .) A white, brittle hy- drocarbonate of magnesia, found at Hoboken, N. J., and Texas, Pa. Sp . gr . 2-145. Hydromel, n. [Gr. hudor , water, and mel i, honey.) A liquid consisting of honey and water. Hydrometeors, n. pl. [From Gr. hudor , water, and meteor a, meteors.] A term generally applied to the aqueous phenomena of the atmosphere, as rain, snow, hail, ., taken collectively; - but also sometimes used in the singular. Hydrometer, n. [Fr. hydromètre; Gr. hudor , water, and metron , measure.) An instrument for measuring the relative densities, or specific gravities, of fluids; and thence the strengths of spirituous liquors, which are inversely as their specific gravities. The principle upon which the ordinary hydrometer is constructed is as fol- lows: When a body is immersed in a fluid, it loses as much of its weight as is equal to the weight of the fluid which it displaces. Thus, if a body be suspended from one arm of a balance, and counterpoised by applying weights to the other arm; and then, while suspended, it be immersed in water, it will be found that the coun- terpoising weight is not sufficient, and in order to re- store equilibrium, a weight equal to the weight of the water displaced must be added. If, then, the same body be immersed in two different fluids, the weights which it will respectively lose in each will be directly prop or- tional to the specific gravities of the fluids; because the lo of weight is always equal to the weight of the fluid displaced, that is, the magnitude of the body multi- plied by the specific gravity of the fluid. The same principle holds good in the case of substances which are lighter than the fluid; for when a body floats upon the surface of a fluid, the weight of the portion of fluid displaced is equal to the weight of the floating body. All the instruments called hydrometer , or aërometer, are constructed upon this principle in hydrostatics. Baumé's (Fig. 1341) is generally recognized in the U. States, and is much used on the Continent of Europe, especially for liquids heavier than water. It is made of two sorts, one for liquids lighter, and the other for those heavier than water, and of these there are varieties for special liquids. For acids or salts the instrument is graduated by sinking it first in pure water, and ballasting it so that the water line shall be near the top of the stem. This fixes the zero point. It is then floated in a solution of 15 parts by weight of dry common salt in 85 parts of distilled water; and the point cut by the water line is marked 150. From these the whole stem is divided into degrees, which should reach to 66° for sul- phuric acid. The greater the degree indicated in its use, the more dense is the fluid. For spirituous liquors the zero point upon the stem is determined from a solution of 10 parts of dry salt in 90 of water, in which nearly the whole of the stem should be out of the fluid. The 10- degree point is given by pure water, and the degrees are from these marked upward, even to 70° for sulphuric ether; the larger the degree indicated the lighter the fluid. Instruments for special uses are made from these, but with short range adapted for their particular service. The specific gravity of a liquid is ascertained Fig . 1341. from the indication of the H. of the first cla IMG:content-0660.png:[blocks in formation] a series of tables calculated for the purpose. In these tables, under the proper temperature, will be found the percentage of strength required.