T7 



HYDRAULIC RAM. 



HYDROCKI.l. 



: 



U Y OKAl'LIC RAM. [HYDRODYNAMICS.] 



HYDRAULICS. That branch of science which includes the phe- 

 nomena of fluid in motion, and the modes of obtaining from them 

 useful results. It is usually limited to what are called incompressible 

 fluid* or liquid*, and may relate 1st, to the laws of the effluence of 

 water from a reservoir ; 2dly, to running-waters ; Srdly, to the use of 

 water as a motive power ; 4 thly , to nmAhM. for raising water. For 

 the theoretical part of the subject we refer to HYDRODYNAMICS. Its 

 applications will be found under HYDRAULIC Pans; PUMP; SYPHON ; 

 SC*KW.ABCBUIIDIA; WATER- WH*M.;WATER-MACHiNE;TuRBiNi,4o. 



HYDRIDES. Compounds containing hydrogen in combination 

 either with an element or a compound radical, wit not forming an 

 integral part of a compound radical, are termed hydride*. Thus the 

 bodies (C,H,)H and AsH, are termed respectively hydride of methyl 

 and terhydride of arsenic ; but the compound radical methyl (C,H.) U 

 not termed a hydride, because in its relations to other bodies it plays 

 the part of a simple or elementary substance. [ORGANIC RADICALS.] 

 The term hydride, as applied to the inorganic compounds of hydrogen, 

 has almost become obsolete, other forms of nomenclature being utmost 

 exclusively used for such compounds. Thus we do not call the com- 

 pounds of hydrogen with sulphur, nitrogen, and chlorine, hydrides, 

 but sulphuretted hydrogen, ammonia, and hydrochloric acid. On the 

 other hand, the term hydride has received very extensive application 

 in naming organic compounds, amongst which we find hydrogen 

 united, in the sense above described, both with positive and negative 

 radicals. 



Hydride* of Ponlire Radical*. These bodies, isomeric with the 

 positive radicals themselves, constitute on important class of hydro- 

 carbons. They are met with amongst the products of the destructive 

 distillation of organic substances, and can also be formed by two other 

 reactions, namely : 



1st. By heating the potash salts of certain acids with excess of 

 hydrate of potash. In this way hydride of phenyl [BENZOLE] is 

 produced by heating benzoate of potash with hydrate of potash : 



C..H. 



Hydrate of 



potash. 



+ 2KOCO, 



Benxotteof 

 potajh. 



2nd. The hydrides of the positive radicals are formed by the action 

 of water upon the zinc compounds of the positive radicals, thus : 



+ HO = ZnO + 



Zincmetbyl. Hydride of methyl. 



The following are the principal known hydrides of positive 

 radicals: 



I. IN THX ETHYL FAMILY. 



Formula! 



Hydride of methyl, or light carburetted hydrogen . * j[ ' ! 

 Hydride of ethyl C *^ 5 J 



Hydride of amyl C "H"J 



II. In TBS PHXXTL FAMILY. 

 Hydride of phenyl, or benzole ... 



C,, 



Hydride of toluonyl, or toluol 

 Hydride of cumenyl, or cnmol 

 Hydrid* of cymenyl, or cymol 



H'} 



They are also very prone to change into isomeric compounds. With 

 the bisulphates of the alkalies they form crystalline compounds. They 

 are powerful reducing agents, throwing down metallic silver when 

 heated with the solution of the ammonio-nitrate of that metal. 



The following are some of the chief hydrides of negative radicals :- 



Some hydride* of positive radicals are gases, others liquids or solids 

 They are remarkable for their stability and resistance to chemica 

 agent*. Paraffin probably belongs to this class of organic compounds. 



Hydride* of ffegalire Radical*. These bodies, commonly terniec 

 aldehyde* (from alcool dehydroyenatum), are intermediate between the 

 alcohol* and the derived acids, thus : 



Alcohol. 



Aldehyde. 



Acetic acid. 



They are generally formed by the action of oxidising agents upon 

 the alcohols ; oenanthylic aldehyde is obtained by the dry distillatioi 

 of castor oil, whilst a few others are met with ready formed in essentia 

 oils. The hydrides of the negative radicals are as remarkable for their 

 instability as those of the positive are for the opposite property. The; 

 rapidly attract oxygen from the air and pass into the correspondin) 

 acids ; thus, vinic aldehyde pnsiM into acetic acid : 



Formula'. 



I. IN inr. Anmc FAMILY. 



Hydride of ethyl, or aldehyde 



Hydride of proplonyl ' 



Hydride of butyryl C , H J 



Hydride of raleryl c . n tt J 



Hydride of o?nanthyl " "n'j 



Hydride of palmityl c H ,iO, I 



II. IN TIIE Aravuc FAMILY. 

 Hydride of ucryl, or aeroleln ... 



III. In rax BEXIOIC FAMILY. 

 Hydride of benzoyl, 01 oil of bitter almonds 



Hydride of cumyl, or cuminol . 





C. 



.H.O.J 



c f . Hll o,j 



Descriptions of the positive and negative hydrides will be fnund 

 under the respective radicals. 



HYDRINDIN. [INDUIO.] 



HYDHIODIC ACID. [loomt.] 



HYDRO. A chemical prefix, see CHEMICAL NOMENCLATURE. No- 

 menclature of Acid*. 



HYDROBENZAMIDE. [BENZOLONE; HYDRAMIDES.] 



HYDROBENZILE (C^E,/),). A product of the action of sulphide 

 of ammonium upon benzUe. It is a colourless crystalline body, soluble 

 in alcohol and ether, insoluble in water, fusing at 117 Fahr., and dis- 

 tilling unchanged. It possesses an odour like that of oil of bitter 

 almonds. [BENZOic GROUP.] 



HYDHOBENZOINAMIDE. [BEXZOINAMIDE.] 



HYDROBROMIC ACID. [BROMIXK.J 



HYDROCARBONS. This name is applied to a very numerous 

 class of chemical compounds consisting of carbon and hydrogen. The 

 chief hydrocarbons whose constitution is well known are the monatomic 

 and biatomic radicals, the double radicals, and the hydrides of !].. 

 monatomic radicals. In addition to these, however, a host of other 

 similar compounds of less certain constitution are met with amongst 

 the products of the destructive distillation of animal and -vegetable 

 substances ; the illuminating effect of coal gas, for instance, in due 

 exclusively to certain gaseous and volatile hydrocarbons, whilst coal 

 tar and wood tar are rich in the same class of compounds. 



A large number of hydrocarbons, of which defiant gas may be taken 

 as a type, contain an equal number of equivalents of the two elements, 

 their composition being expressed by the general formula CiiHn, n re- 

 presenting an even number, as 2, 4, 6, &c. Two other families contain 

 an excess of hydrogen; these are represented respectively by the 

 formulas CnHn + 1 and CnHn + *. Another class, (to which benzole 

 belongs, has the composition CnHn 6, whilst naphthalin seems to re- 

 present a similar family of the form CnHn 12. Other hydrocarbons, 

 of the form CnHn 1 and CnHn 7, appear also to exist, although 

 they are less extensively known than the other families. As regards 

 their state of aggregation, some hydrocarbons are gaseous, as olefiant 

 gas, others liquid, as benzole, and others solid, as naphthalin and paraffin. 

 The hydrocarbons of the form CnHn and CnHn 12 are readily acted 

 upon by chlorine, bromine, and other agents ; whilst the families 

 CnHn + l and CnHn + 2 are remarkable for their great inditl< 

 towards chemical reagents, a characteristic which has given to one of 

 them the name paraffin. [ORGANIC RADICALS ; HTDRII>I>.| 



HYDROCELE (from 'Map, water, and ic^\r>, a tumour) is a collection 

 of watery fluid in the tunica vaginalis testis. It is characterised by 

 the formation of a tumour, which enlarges gradually without heat or 

 pain, has a pyriform shape, is firm and elastic, often appears trans- 

 parent when a light is placed behind it, and does not, like a 1 

 diminish in size when the body is in a recumbent posture, nor commu- 

 nicate any impulse when the patient coughs. In most cases the fluid 

 collects without any distinct cause ; but in some it follows rapi'lU 

 after an injury of the part. The quantity of fluid which accumulates 

 varies from a few ounces to four or six pints. The disease often occurs 

 in those who are otherwise in perfect health, and in persons of all ages; 

 it may be seated on one or both sides of the body. The treatment 

 consists, 1st, in the evacuation of the fluid by tapping; and, 2nd, in 

 preventing it from accumulating again by exciting such active inflam- 

 mation of the opposite surfaces of the tunica vaginalis as may produce 

 their adhesion and the obliteration of the cavity. The latter purpose 

 is generally fulfilled by the injection of some stimulant fluid, or the 

 introduction of a foreign body into the cavity. 



