CARBON AND THE HYDROCARBONS 37$ 



Acetylene is also produced in all those cases where organic sub- 

 stances are decomposed by the action of a high temperature for 

 example, by dry distillation. On this account a certain quantity is 

 always found in coal gas, and gives to it, at all events in part, its 

 peculiar smell, but the quantity of acetylene in coal gas is very small. 

 If the vapour of alcohol be passed through a heated tube a certain 

 quantity of acetylene is formed. It is also produced by the imperfect 

 combustion of defiant and marsh gas for example, if the flame of 

 coal gas has not free access to air. 49 The inner part, of every flame 

 contains gases in imperfect combustion, and in them sorno amount of 

 acetylene. 



Acetylene, being further removed than ethylene from the limit 

 C u H 2lM . 2 ^ hydrocarbon compounds, has a still greater faculty of combi- 

 nation than is shown by olefiant gas, and therefore can be more readily 

 separated from any mixture containing it. Actually, acetylene not 

 only combines with one and two molecules of I 2 , HI, H 2 SO 4 , C1 2 , Br 2 , 

 &c. . . . (many other unsaturated hydrocarbons combine with them), 

 but also with cuprous chloride, CuCl, forming a red precipitate. If a 

 gaseous mixture containing acetylene be passed through an ammoniacal 

 solution of cuprous chloride (or silver nitrate), the other gases do not 

 combine, but the acetylene gives a red precipitate (or grey with silver), 

 which detonates when struck with a hammer. This red precipitate 

 gives off acetylene under the action of acids. lu this manner pure 

 acetylene may be obtained. Acetylene and its homologues also 

 readily react with corrosive sublimate, HgCl 2 (Koucheroff, Favorsky). 

 Acetylene burns with a very brilliant flame, which is accounted for 

 by the comparatively large amount of carbon it contains, 50 



The formation and existence in nature of large masses of petroleum 

 or a mixture of liquid hydrocarbons, principally of the series C n H 2n4 . a 

 and C,,H 2n is in many respects remarkable. 51 In some mountainous 



* 9 This is easily accomplished with those gas burners which are used in laboratories 

 and mentioned in the Introduction. In these burners the gas is first mixed with air in a 

 loug tube, above which it is kindled. But if it be lighted inside the pipe it does not 

 burn completely, but forms acetylene, on account of the cooling effect of the walls of the 

 metallic tube ; this is detected by the smell, and may be shown by passing the issuing 

 gas (by aid of an aspirator) into an ammoniacal solution of cuprous chloride. 



40 Amongst the homologues of acetylene C n H 2 r-^, the lowest is C 3 H 4 ; allylene,, 

 CH 5 CCH, and allene, CH 2 CCH 2 , are known, but the closed structure, CH 2 (CH) 2 , is 

 little investigated. 



51 The saturated hydrocarbons predominate in American petroleum, especially in 

 its more volatile parts ; in Baku naphtha the hydrocarbons of the composition CnH 2 form 

 the main part (Lisenko, Markovnikoff, Beilstein) but doubtless (Mendeleeff) it also con- 

 tains saturated ones, CH 2M + 2 . The structure of the naphtha hydrocarbons is only known 

 for the lower homologues, but doubtless the distinction between the hydrocarbons of the 

 Pennsylvanian and Baku naphthas, boiling at the same temperature (after the requisite,. 



