of Heat and Pressure upon the Paraffins. 



201 



13. This mode of decomposition would appear to be general, at least 

 for the higher terms of the series of normal paraffins. If these bodies be 

 represented constitutionally by linking the carbon atoms together in a 

 single chain, 



CH 3 — CH— CH— CH 2 — CH 2 CH 3 , 



then the simultaneous formation of hydride and olefine must be assumed 



to occur from the loosening of the affinities of certain of the groups of 



CH 2 . Under the influence of heat these groups become dissociated 



(vibrate without the spheres of their mutual attractions), and recombme 



to form saturated hydrocarbons. Assuming (for the sake of simplicity) 



that this decomposition can occur so low down in the series as in the case 



of butane, it might be thus represented : — 



HHHH HH HH 



I I I I II II 



H — C — C — C — C — H = II — C — C — H + C= 



I I I I II II 



HHHH HH HH 



We can offer but little direct evidence as to the exact manner of this 

 decomposition — whether it is attended by the gradual elimination of 

 ethylene, a hydride containing a greater number of carbon atoms being- 

 left behind, or whether the paraffin is at once split up into the hydride 

 and an olefine containing an equal number of carbon atoms as in the above 

 equation. Neither supposition is exactly substantiated by experiment. 

 If the action of heat gave rise to the former mode of decomposition, we 

 ought to obtain a large quantity of ethylene after prolonged heating, 

 especially when the liquid portion is rich in hydrocarbons of low molecular 

 weight ; but, as we have already pointed out, the process of liquefaction is 

 accompanied with the production of comparatively little gas. On the 

 other hand, an examination of the amounts of bromine required to render 

 the hydrocarbons boiling below 200° permanently red, shows that the 

 proportion of hydride to olefine in the several mixtures becomes gradually 

 larger as the molecular weight increases. It would appear, therefore, 

 that the liquids boiling between 200° and 300° are not mixtures of hydrides 

 and olefines in equal proportions, as are the fractions boiling at 65-70° 

 and 94-97° &c. 



It would have been doubtless interesting to have determined the relative 

 amounts of the 12 fractions isolated from the decomposed paraffin ; but 

 when it is considered that their separation was only effected after several 

 thousand distillations, it will be evident that the quantities obtained after 

 such tedious treatment can afford no real indication of the amount present 

 in the original liquid. We have, however, a distinct impression that the 

 amounts of liquid boiling at 94-97° and 122-125° were but slightly (if 

 at all) less than the quantities boiling at 252-255° and 273-276°. 



VOL. XXI. 



