HYD 



HYD 



gent, gaseous acid formed ol' one oq. 

 fluonne, and one hydrogen. Hce Fia- 

 orinc. 



HYDROGEN. Inflammable air. 

 The lightest body in nature : an ele- 

 mentary gas, without o(k)ur or colour, 

 very inflammable in air, forming ex- 

 plosive eompounds with oxygi-n. It 

 has little chemical activity alone, and 

 is irrespirable : 1 00 cubic inches weigh 

 2-13 grains. Its equivalent is 1 on 

 the hydrogen scale, and 12 5 on the 

 oxygen ; symbol H. Hydrogen does 

 not exist uncombined in nature ; but 

 in a compound state, in water, annno- 

 nia, and vegetable products, is large- 

 ly accumulated. It combines with 

 oxygen, forming water, by the aid of 

 heat or electricity. In all its prop- 

 erties hydrogen resembles a metal. 

 It combines with oxygen, chlorine, 

 bromine, &c., in the same way as 

 other metals, and is readily displaced 

 by the greater number, sometimes 

 with the evolution of pure gas, at oth- 

 ers by the simultaneous combination 

 of the liberated hydrogen with oxy- 

 gen, to form water. Its compounds 

 with carbon, forming coal gas and oil 

 gas, are of considerable economical 

 value : these, with sulphuretted hy- 

 drogen, are also thrown out from wet, 

 putrescent manures, stagnant ditch- 

 es, &c. For other compounds, see 

 the usual names. 



Some writers state that plants pos- 

 sess the property of decomposing wa- 

 ter and appropriating its hydrogen ; 

 but this has never been proved : the 

 decomposition is readily effected by 

 galvanism. Plants contain six to sev- 

 en per cent, of hydrogen in the dried 

 portions without the water, in which 

 there is one ninth by weight : fats and 

 waxes contain ten to thirteen per 

 cent. 



HYDROMETER. Areometer. An 

 instrument to take the specific grav- 

 ity or density of fluids, spirits, &c. 

 It is of great value in testing the 

 strength of spirits, of solutions, of 

 sugar, dyestufis, &,c. The form of 

 the implement, which is made of 

 brass or glass, is shown in the fig- 

 ure. It is sometimes furnished with 

 a series of weights, ^\', which are pla- 



ced on the short stem, 

 D, to enable it to sink in 

 different solutions. The 

 stem A B is usually Hat 

 and graduated ; the scale 

 depending upon the use, 

 and varying with the ma- 

 ker. .Sykes's instrument, 

 which IS used for taking 

 the strength of spirits, is 

 furnished with a table. 

 Baume's areometer, or hy- 

 drometer, is extensively 

 used by sugar-makers and 

 manufacturers. It is grad- 

 uated from a central point in the 

 stem, — upward, for fluids lighter than 

 water, and -{- below, for those that 

 are heavier. The (zero) marks the 

 density of distilled water at 58° Fah- 

 renheit, and the downward marks cor- 

 respond to the density of solutions 

 of salt and water, containing for each 

 mark an additional one per cent, of 

 salt ; thus, 5° indicates a fluid of the 

 same density as that produced by 

 mixing 5 parts common salt and 95 

 water. The real specific gravities are, 



HYDROPHILID.E. Aquatic, pen- 

 tamerous beetles. They are vegeta- 

 ble feeders. 



HYDROPHOBIA. See Dog. 



HYDROPHYTES (fromvcJwp, and 

 dvrov, a plant). Plants hving in fresh 

 water. 



HYDROSTATIC BALANCE. 

 The common balance, furnished with 

 a scale that may be suspended near 

 the beam, and under which a hook is 

 placed to hang any substance to be 

 weighed in water. See Gravity, Spe- 

 cific. 



HYDROSTATIC PRESS. See 

 Press, Hi/draulic. 



HYDROSTATICS (from i'(5op, and 

 arau, I stand). The science which 



411 



