H Y D 



[221 ] 



H Y D 



then termed water of crystallization. 

 The hydrates are numerous, as hy- 

 drates of alumine, baryta, cobalt, 

 copper, lime, magnesia, potassa, 

 soda, &c., &c. 2. Any uncrystal- 

 lized substance which contains 

 water in a fixed definite proportion. 

 HYDRAU'LIC \ (vdpavXis, Gr. hy~ 

 HYDRAU'LICAL. > draulicus, Lat. hy- 

 HYDRAU / LICK. ) draulique, Fr. idrau- 

 lico, It.) Relating to the convey- 

 ance of water through pipes. The 

 siphuncle of the nautilus, ammon- 

 ite, belemnite, &c., forms a very 

 beautiful and complete hydraulic 

 apparatus. 



HY'DRAULICS. The science of the 

 motion of fluids, and the construc- 

 tion of all kinds of instruments and 

 machines relating thereto. 

 HY'DRO. As a prefix, denotes that 

 hydrogen enters into the composi- 

 tion of the substance which it sig- 

 nifies. 



HY'DROGEN. (from vSwp and ryeiWw, 

 Gr.) One of the simple, or ele- 

 mentary bodies. Inflammable air, 

 proved by Cavendish to be the 

 basis of water, from which circum- 

 stance it has obtained its name. It 

 is obtained by the action of iron or 

 zinc on dilute sulphuric acid. Hy- 

 drogen is colourless, and has com- 

 monly a slight odour of garlic ; it 

 is not absorbable by water ; it is 

 devoid of taste, and is destructive 

 of life when respired for any time. 

 It is the lightest body known, 100 

 cubic inches weighing only 2.25 

 grains, or being nearly thirteen 

 times lighter than atmospheric air. 

 It is combustible, and, when pure, 

 burns with a yellowish-white 

 flame. Hydrogen enters into the 

 composition of all waters, and is 

 evolved in a compound state from 

 volcanos, from certain fissures in 

 the earth, and in districts where 

 coal is found. Two volumes of 

 hydrogen unite with one of oxygen 

 in the production of water. As 

 far as the superficies of our planet 



is concerned, water so predomi- 

 nates, that, at first sight, hydrogen 

 might be considered as constituting 

 a substance of more relative abund- 

 ance than it really does. The 

 quantity of hydrogen locked up in 

 coal is considerable. According to 

 Dr. Thomson, cannal coal contains 

 21 per cent, of it, although in the 

 Newcastle caking coal the propor- 

 tion is but a trifle more then 4 per 

 cent. Hydrogen may be considered 

 as the most important substance of 

 its class next to oxygen, which 

 enters into the composition of the 

 earth* s crust. Symbol H. 



HYDRO' GENATED. Combined with hy- 

 drogen. 



HYDRO'GENOUS. (from uftwp. water, 

 and <yevvdiv, to produce, Gr.) Pro- 

 duced by the action of water, as 

 hydrogenous rocks or strata. Among 

 the older rocks, as among the newer, 

 two entirely distinct classes occur, 

 namely, pyrogenous and hydrogenous 

 deposits. 



HYDRO'GRAPHY. (from vScop and 

 <y/>a0o>, Gr. idrogrqfia, It. hgdro- 

 graphie, Fr.) Description of the 

 watery part of the globe ; the art 

 of measuring and describing the 

 sea, rivers, canals, lakes, &c. With 

 regard to the sea, it gives an ac- 

 count of its tides, counter-tides, 

 soundings, bays, gulfs, creeks, &c., 

 as also of the rocks, shelves, sands, 

 shallows, promontories, harbours; 

 the distance and bearing of one 

 point from another; with every 

 thing that is remarkable either at 

 sea or on the coast. 



HYDRO'IDA. The second order of the 

 class Hydrozoa, comprising the 

 medusa, hydra, &c. 



HYDRO'METER. (from v&wp and pA7pov, 

 Gr. hydrometre, Fr. idrometro, It.) 

 An instrument for measuring the 

 extent or depth, gravity, density, 

 and velocity of liquids. 



HY'DROPHANE. (from v8wp and (fiaivw, 

 Gr.) Called also changeable opal. 

 Silex Hydrophaue of Brongniart. 



