3-14 PKINCJPLKS OF CHE.MISTKY 



potassium. ( >n the application of more or less heat, all hydrocarbons 

 decompose, 2:i forming charcoal and hvdr< gen. The majority of hydro- 

 carbons do not combine \vith the oxygen of the air or oxidise at ordi- 

 nary temperatures, lint under the action of nitric acid and many other 

 oxidising substances most of them are subject to oxidation, in which 

 either a jiortion of the hydrogen and carbon :.- separated, or the oxygen 

 outers into coin bin at ion. or else the elements of hydrogen peroxide enter 

 into combination with the hydrocarbon.- 1 When heated in air. hydro- 

 carbons luirii. and, according to the amount of carbon they contain, 

 their combustion is attended with a separation of soot that is. linely- 

 dividod charcoal which imparts great brilliancy to the Hamo, and on 

 this account many of them are used for the purposes of illumination 

 as. tor instance, kerosene, coal u'as, oil of turpentine. As hydrocarbons 

 contain reducing elements (that is. those capable of combining with oxy- 

 gen) they often act as reducing agents as. for instance, when heated 

 \vith oxide of copper, they burn, forming carbonic anhydride and water, 

 and leayo metallic copper. According to Gerhardt. all hydrocarbons 

 contain an even number of hydrogen atoms. Therefore, the general 

 formula for all hydrocarbons is (' II., whore n and /// are Nvholr- 

 ntimbers. This fact is known as tin- ///// <>/' >/> ,, mmifti't'n. Ht^nce, tlu v 

 simjile>t possible hydrocarbons ought to be: C.'Il.,, ('H,, dl,, . . . 

 C.J1,, (,'.,11,, C.JI*,, (, < .JI S . . . but all of them are not in existence, as 

 they are subject to certain limitations. 



Some of the hydrocarbons are capable of combination, whilst others- 

 do not show that power. Those "which contain less hydrogen belong to 

 the former category, and those which, for a given quantity of carbon, 

 contain the maximum amount of hydrogen belong to the latter. The 

 composition of tho>e last mentioned is expressed by the general formula 

 C,,!!.,,, ,. Thoe >o -railed ant n rated />>/</rnr<tr/><>>i* are incapable 

 of combination.-' ! ud^inn' from this, the hydrocarbons ( 'H ( , (\, H s . 



when ni^iilurat.-il li\ .Irncarl.mi-, sir,, slmki-n willi M 



form '.-Ivr..!- i.,r i-xiiini.!.-, C.H, yii-lils (Ml, ; <),. 



1 M\ iii'ticlr 1,11 lln- Mil.j.-r-t iippcarcd iii tin' jnunial (if tlir Si. I'rdT-liiir- Acadcinv 

 of Science- in Isr,l. Cp i,, |li ; ,t time, .-iltlinii-li Mian\ a(l(liti\c c'Hiuliinations witli livdro 

 1-iirl.un-, MIL I tln-ir fli-ri\.iti\e- U.T,. knowii. tlie\ lia.l iml l.eeii ^enei-aliserl, and were even 



c()nlinnall\ i|iiited a- .,,-,-- ,,t -id.-i it ut i. ,n. Tim-, tin- c. .ml.in.it i. f etliylene, ( '.,H ,, 



with ehlni-ine. ('!,. w,i- i. ('ten i-e-ardi-il a> .1 fdriiiiitiiin d tin- pnidncts of the >nl^t it ut ion 

 r.f C.H-CI iiinl HCI i iip|o-,ed were held to-Hher a- fh.' W ater of crystullisn 



tidii i- in -all . I. eariici th.ui ll,,. [*:>!. J,,u n/nl t,f' Hi, I', t , ,,//>/// .] r,i, i, -,,,,/ 1 I 

 . . ..iii|.iiinU. In general, accordin- to the law of limits.. 



