HYD 



383 



HY'DRO-FLUOSIL'ICXTES, salts formed by 

 the hydro- fluosilicic acid with bases. 



HY'DRO-FLUOSILIC'IC ACID, a. compound 

 acid consisting of, 1, hydrofluoric acid, and 

 2, fluosilicic acid (in simple mixture, ac- 

 cording to Ber/elius.) 



HY'DROGEN, from iiSug, -water, and 

 yiva;, to produce. An inflammable, co- 

 lourless, and aeriform tluid, the lightest 

 of all known substances, and the basis of 

 water (q. v.). It is plentifully distributed 

 in nature. It is one of the ingredients of 

 bitumens, oils, fats, alcohol, and in fact 

 of all animal and vegetable bodies. It is 

 speedily fatal to animal life when taken 

 into the lungs ; it does not support com- 

 bustion, but uniting with oxygen much 

 light and heat are evolved. Being the 

 tightest ponderable substance known, it 

 is usually assumed as unity in describ- 

 ing the sp. gr. of gases. 



HY'DROGE.NATED, combined with hy- 

 drogen. 



HY'DROORAPHY, from v^taf, water, and 

 yectQM, to describe. Description of the 

 watery part of the terraqueous globe, as 

 seas, lakes, &c. It gives an account of 

 tides, soundings, bays, gulfs, creeks, 

 sands, shoals, &c. ; the distances and 

 bearings of objects from one another, and 

 whatever is remarkable, either at sea or 

 on the coast. It also comprehends the 

 construction of maps and charts for the 

 use of navigators, &c. 



HYDROG'URETS, compounds of hydrogen 

 with a simple inflammable body, as car- 

 bon, phosphorus, or sulphur, or with me- 

 tals: e. g., carburetted hydrogen is a hy- 

 droguret of carbon, 



HY'DROMANCY, iibcae, and [Aatvr-iet, pro- 

 phecy. Among the ancients a method of 

 divination by water. 



HYDROM'ETER, from 

 fAir^ov, measure. An 

 instrument in com- 

 mon use for finding 

 the specific gravity of 

 non-elastic fluids. It 

 < insists of a hollow 

 ball of glass or metal 

 with a weight below 

 it, and a slender stem 

 above, divided into a 

 certain number of de- 

 grees by marks. In 

 pure water it is ad 

 justed to float at a 

 particular mark, but 

 when immersed in a 

 lighter or heavier li- 

 quid it floats higher 

 or sinks lower. Sometimes the instru- 

 ment is adjusted to different fluids by 

 movable weights, while the gradua- 

 tions of the stale are made to express 





HYD 



the specific gravities by the degree to 

 which it sinks. The figure represents 

 Silk's hydrometer, where A is a brass 

 ball loaded with a weight B. and sur- 

 mounted by a slender stem D, graduated 

 into eleven equal parts. It is provided 

 with eight weights C, in which a slit is 

 cut so as to admit the slender part of the 

 stem B into the hole in the centre. The 

 use of these weights is to adjust the in- 

 strument to fluids heavier than water, 

 and in which it would not otherwise sink 

 to the level of the lowest division on the 

 stem 1). This is the instrument ordered 

 by Act of Parliament for collecting the 

 revenue on ardent spirits. 

 HY'DRO-OX'IDE, a hydrated oxide. 



HYDliOl'ERSULPHU'BlC AclD, Or BlSUL- 



PHURET OF HYDROGEN. A compound of 

 2 of sulphur, and 1 of hydrogen. 



HYDROPH'ANE, from iSwj. water, and 

 0<wu, to show. A variety of opal, which 

 is opaque when dry, but by immersion in 

 water becomes transparent. 



HYDROPH'ILUS, a genus of aquatic in- 

 sects, vZtug and <piko;. The hydrophilii, 

 form the first tribe of the palpicorne fa- 

 mily of pentamerous coleoptera in Cuvier's 

 arrangement, but in the arrangement of 

 Linnajus they form a division of his genus 

 Dytiscus. They are variously subdivided. 



HYDROPHO'BIA, from i/Stug, water, and 

 $opu, to fear. Canine madness, which is 

 always accompanied with a preternatural 

 dread of water. Pathologists usually 

 regard the disease as the consequence of a 

 morbid poison, introduced into the system 

 by the bite of a rabid animal. 



HYDROPHTHAL'MIA, from ii^u^, water, 

 and o$6a\u,as, the eye. A morbid en- 

 largement of the eye, arising from a pre- 

 ternatural increase of the vitreous or 

 aqueous humours. The same name is also 

 given to a mere cedematous swelling of 

 the eyelid. 



HYDROPH'YTJE, water-plants, vtiu*, 

 water, and ^ti<rsx,aplant. Thenumberof 

 hydrophytes is very considerable, and their 

 situations are more various than could 

 have been anticipated. Some are covered 

 and uncovered daily by the tide ; others 

 live in abysses of the ocean, at the extra- 

 ordinary depth of 1000 fee t ; and although , 

 in such situations, there must reign dark- 

 ness more profound than night, many of 

 these vegetables are highly coloured. 



HYDROPNEDMAT'IC TROUGH. A name 

 which has been given to the apparatus 

 more commonly called the pneumatic 



HY'DROPS, dropsy, vfyarj/, from utca{, 

 water. A preternatural hydropoid col- 

 lection in the cellular substance, or differ- 

 ent cavities of the body. Anasarca, hy- 

 drocephalus,hydrothorax, ascites, hydro- 



