HYDRAULIC RAM. 368 HYDROCARBONS. when the ratio exceeds 1-12 (i.e. 1 foot fall for 25 fi'ot raised). Wliere the fall is great, llie wear and toar on the ram is excessive. Some au- tliorities give the desirable working limit for a hydraulic ram as IVj to 10 feet fall of drive water and a lift of not over 250 feet, but with so great a lift a large proportion of the water will l)e wasted. The ram. as described, was in- vented by .Joseph Michael dc .Montgolfier, of France, in 1790; but in 1772 an Englishman named John Whiteliurst built a machine embody- ing the same principle, cxccot that the valve at the foot of the drive-pipe had to be closed by hand. His device was described in the J'liilo- S()i>hical Transactions for 1775. Many improve- ments have been made in the machine of Mont- gollier, the most important of which, perhaps, aim to lessen the shock of the operation of the valves. Springs have been used to that end; the drive-pipe valve has been counterweiglitcd, and a portion of the air compressed in the chamber lias been used to drive a small air-motor, so con- nected as to aid in the gentle closing of the valve at each cycle. Anollier improvement is the equipment of rams so that a supply of dirty water may be used to lift clean water, either when flic supply of the latter is scanty, or is nob available under a sufficient head. Finally, hy- draulic nuns are used to drive pumps, when they are properly classed under pumping engines. See PrMp.s ANM> Pimping M.cuinebv. HYDRAULICS. See Htdrodynamics, and ]lYi)RO.sr.rKS. HY'DRAZINE, or Amidooen, ILX = H,. A basic compound of nitrogen and hydrogen, which may be obtained by heating triazo-acetic acid with water. Hydrazine hydrate, N.H.HjO. is a strong reducing agent precipitating metallic silver and platinum from solutions of their salts. With acids it forms crvstalline salts, such as the hydrochlorides, X.H..Hcl. and N.H.2HC1, the sulphate, N..H,.H,SO„ etc. The hydrogen of hydrazine may be partly replaced by either hy- drocarbon groups, such as methyl (CHj), ethyl (C2H5), phenyl (CjH,). etc.. or organic acid radicals, such as acetyl (CH,CO), benzoyl (C, H:.CO), etc. The most important of these organic derivatives of hydrazine is phenyl hydrazine, CoH.HN ^ NHj. The benzoyl compounds in- clude benzoyl-hydrazine. CnH^CO.HN = NH.. and symmetrical dibenzoyl-hydrazine, C«HjCO.HX= Nll.COCJf:,. The presence of hydrazine in aque- ous solutions may be readily detected by the use of a few drops of benzaldehyde, with which it forma a yellow crystalline precipitate of ben- zalazine. C„H„CH.N ^ Nil;.. Compounds of simi- lar constitution are formed by the action of hydrazine on other aldehydes. See DlAZO-CoM- POl'NDS. HYTJRIDE. A name applied, in chemistry, to the ciimpnunds of the metals with hydrogen. Notable hydrides are those of palladium, sodium, potassium, calcium, strontium, barium, and mag- nesium. The hydrides have, at least as yet. no practical value; but when more thoroughly in- vestigated they will present considerable interest in connection with the doctrine of valency (q.v). The term hydride was formerly employed in con- nection with certain hydrocarbons. HY'DRIODIC ACID (from ;ii/<ir-ogen -f lorf-ine) . HI. An acid compound of hydrogen and iodine, analogous to hydrochloric acid. It may be prepared by the action of phosphoric acid on potassium iodide, in its isolate I state, it is a colorless gas with an odor resembling that of hydrochloric acid. Usually it is kept in aqueous solution, and is thus employed in a number of chemical processes. It decomposes somewhat easily into its components, hydrogen and iodine, and by giving up its liydiogen acts as a reducing agent. The salts of liyilriodic acid are termed iudides (q.v.). Hydriodic acid is sometimes used medicinally instead of its salts. HY'DRIOTAPH'IA, or URN BURIAL. A quasi-scientific, quasi-religious treatise by Sir Thomas Browne (1058). Its explanatory subtitle is: A Discourse of the Sepulchral Urns Lately Found in Norfolk, which leads to the account of the rites of burial of various ages, and ends with an elo(|ueiit disquisition on death and immortal- ity. It shows an acquaintance with Dante re- markable for that age, and was greatly admired by Charles Lamb. HY'DROBRO'MIC ACID ( from /i;/dro-gen + fcromine), IlBr. An aciil coiii|iound of hydrogen and bromine, analogous to hydrorliloric acid. It may be prepared by the action of phosphoric acid upon potassium bromide. In the isolated state it is a colorless gas with an odor resembling that of hydrochloric acid. Like the latter, it is very soluble in water, the solution being sometimes used in synthetic chemistry. The salts of hydro- bromic acid are termed bromides (q.v.). HY'DR0CART30NS (from /ii/dro-gen + car- bon). A class of chemical compounds containing only carbon and hydrogen. Their commercial value is very considerable inasmuch as they form the principal ingredients of petroleum, illuminat- ing gas, caoutchouc, gutta-percha, essence of tur- pentine, etc. They are the simplest of the com- pounds of carbon, and the fundainental ideas of organic chemistry have been derived largely from a careful study of their properties and reactions. They are obtained when various organic sub- stances are subjected to a process of destructive distillation, and are subdivided principally into aliphatic, or fatty, and aromatic hydrocarbons. Fatty HYDltocARnoNS. These form an impor- tant class, and arc subdivided into the paraffin, olefin, and acetylene series. (1) The Paraffins, or saturated hydrocarbons of the methane series, are very stable com- pounds and do not react even with the strongest acids and alkalies; hence their name, parafTins, derived from the Latin parum affmis, which means 'having little aflfinity.' Large quantities of them occur in nature as petroleum, natural gas, ozokerite, etc. They are al«o obtained by the destructive distillation of coal, cannel. shale, etc. When they are arranged in the order of their molecular weights, the following 'homolo- gous series' is obtained: Mpthnne, CH,, motwiilar woiiitit 16. Ethane. C,H„, molecnlfir weleht 30. Propane, CjH,, molpcular weight 44. Butanpfl. r,H(o, molpciilar wplp:ht B8. Pentanes, PbHu, molppular wi-i^rht 72. Hexanes, CnH, 4, molecular WPJKht 86. Heptanes, 0,11 „, molecular weight 100. etc. The difference in molecular weight between any two consecutive members of the series is evi- dently the same. It amounts to 14. the sum of the 'weights' of one carbon atom (which is 12) and two hydrogen atoms (which is 2). To obtain the formula of any member, we may substitute a
