H YD 



H YD 



various proportions, forming a series of 

 compounds commonly termed hydro- 

 carburets. 



14. Hydro-chloric acid. An acid con- 

 sisting of hydrogen and chlorine, and 

 long known under the names of spirit of 

 salt, marine acid, and muriatic acid. 

 Some chemists term it chlorhydric acid. 



15. Hydro-chloric ether. An ether 

 which has received the various names of 

 chlorhydric, marine, and muriatic ether, 

 and hypothetically, chloride of ethule. 



16. Hydro-corisa (/coptr, a bug). The 

 Water-Bugs ; a section of hemipterous 

 insects, characterized by their aquatic 

 habit, and by a peculiar form of the body, 

 which has gained for some of them the 

 popular name of boat-flies. See Geocorisa. 



17. Hydro-cyanic acid. An acid con- 

 sisting of hydrogen and cyanogen, and 

 commonly called prussic acid, from its 

 having been procured, though interme- 

 diately, from Prussian blue. 



18. Hydro-dynamics {duva/jm, power). 

 The mechanics of fluids ; or that branch 

 of natural philosophy which investigates 

 the phenomena of equilibrium and mo- 

 tion among fluid bodies, especially such 

 as are heavy and liquid. It is distin- 

 guished into hydrostatics, which treats of 

 the weight and pressure of liquids ; and 

 hydraulics, which treats of their motion. 



19. Hydro-electric machine. A machine 

 constructed by Armstrong on the sup- 

 position that electricity is generated when 

 steam is exposed to friction. On the 

 escape jf steam from certain cocks pro- 

 vided for that purpose, the pressure being 

 70 lbs. on the square inch, an effect 

 is obtained 7 times greater than from a 

 good electrical machine with a plate 3 

 feet in diameter. 



20. Hydro-fluoric acid. A highly corro- 

 sive compound of fluorine and hydrogen, 

 obtained by the action of sulphuric acid 

 upon fluor-spar, or fluoride of calcium, 

 on the application of a moderate heat. 



21. Hydro-gen {■y €vvd(a, to produce). A 

 gas occurring most generally, and abun- 

 dantly, in combination with oxygen, in 

 the form of water. From its inflammable 

 nature, it was formerly called inflammable 

 air; and, from it having been considered 

 the matter of heat, it was called phlogiston. 



22. Hydro graphy {ypd^ta, to describe). 

 That branch of Geography which treats 

 of the water or seas, which compose a 

 part of the terraqueous globe. Hydro- 

 graphical charts or maps are projections 

 of some portion of the ocean, in which the 

 rhumbs, meridians, parallels, &c. with 



170 



the coasts, capes, &c. are laid down for 

 the use of navigation. 



23. Hydr-oida {eJSo?, likeness). An 

 order of the polypipherous Radiata, con- 

 sisting of animals allied in structure to 

 the hydra. They are also called hydri- 

 form polypes. 



24. Hydro-logy {\6fo^, a description). 

 That branch of natural history which 

 treats of water, of its various properties 

 and modes of existence in nature. 



25. Hydro-mancy {/jiavreia, prophecy). 

 An ancient superstition respecting the 

 divining nature of certain springs and 

 fountains ; hence, perhaps, arose the dis- 

 covery of the medicinal virtues of mineral 

 waters. 



26. Hydro-meter {neTpov, a measure). 

 An instrument for measuring the gravity 

 of liquids ; when floating in a liquid, it 

 rises in proportion as the density of the 

 liquid increases; it is graduated from 

 1.000 to 1.060, so as to exhibit at once the 

 specific gravity. 



27. Hydro-metridcB. A family of he- 

 mipterous insects, named from the genus 

 hydrometra, and adapted for walking on 

 the surface of water. 



28. Hydr-ophidcB (ocpi^, a snake). Water- 

 snakes; a family of Ophidian reptiles, 

 characterized by the vertical compression 

 of the tail and hinder part of the body, 

 by means of which they are enabled to 

 swim with facility. 



29. Hydro-phane (.(paivw, to appear). 

 A variety of opal, which is perfectly 

 opaque when dry, but becomes transpa- 

 rent when immersed in pure water. It is 

 also called oculus mundi. 



30. Hydro-^hilidce (^tXeo), to love). A 

 family of coleopterous insects, named 

 from the genus hydrophilus, and charac- 

 terized by their aquatic habits. 



31. Hydro-phytea {(jivrbv, a plant). 

 Plants which grow in water ; a name 

 restricted by botanists to algaceous 

 plants found in fresh-water. 



32. Hydro-silicite. A new mineral 

 found in Serpentine in Siberia, consist- 

 ing apparently of pure silica and water. 



33. Hydro-statics (water standing). 

 That branch of mechanics which treats 

 of the weight, pressure, and equilibrium 

 of fluids, when in a state of rest ; and of 

 these properties of solids, when immersed 

 in fluids. 



34. Hydrostatic balance. A balance 

 for weighing substances in water, in order 

 to ascertain their specific gravities. 



35. Hydro-static bellows. An apparatus 

 for illustrating the hydrostatic paradox t 



