at the Royal Institution, 1 900-1 907. 369 



in methane the single carbon atom is satisfied by and in turn satisfies 

 four single separate atoms of hydrogen — in other words, it is quadri- 

 valent or tetradic.* 



Methane is but one of a long series of hydrocarbons all of which 

 contain carbon and hydrogen in the same relative proportions — those 

 expressed by the formula C,(H2n+2, as there are twice as many atoms 

 and two more of hydrogen as of carbon in the molecule of each 

 hydrocarbon. The petroleum pumped from the oil wells in Penn- 

 sylvania and elsewhere is a very complex mixture of such hydro- 

 carbons, the natural gas from the same wells consisting of methane 

 and other gaseous terms of the series ; petrol, which now plays so 

 important a part hi motor practice, is a mixture of the lower liquid 

 terms, such as pentane, C5H12, hexane, C6H14, heptane, C^Hig ; the 

 petroleum or paraffin oil used in lamps consists for the most part of 

 much higher terms of the series ; the mineral lubricating oils which 

 have rendered such service in the high pressure steam engine, the 

 unguent vaselin and the solid paraffin wax of which candles are 

 made consist mainly of still more complex hydrocarbons similar to 

 methane in composition. 



The name paraffin has reference to the almost complete chemical 

 indifference {par urn affinis) of paraffin waxf ; as all the terms of the 

 series from methane upwards manifest this indifference, the name is 

 now applied to them generally. The fact that they are thus indif- 

 ferent is of significance as a proof that whatever the complexity, 

 whatever the number of carbon and of hydrogen atoms in the 

 hydrocarbon, the affinities of the atoms are mutually satisfied ; if 

 this were not the case, some terms would be more active chemically 

 than others. As hydrogen atoms, ex hypothesis cannot link other 

 atoms together, it follows that in all the terms above methane the 

 carbon atoms must be directly linked together and that only their 

 spare affinities are satisfied by hydrogen. On these assumptions, the 

 paraffins are formulated as chains of tetrad capbon atoms simply 

 linked together by single affinities, thus — 



H H H H H H 



I II III 



H-C-H H-C-C-H H-C-C-C-H 



H H H H H H 



But there is reason to believe that the affinities of the carbon 

 atom can only act in certain directions and that when a number of 

 such atoms are united together they do not form a long straight 

 chain — an uneconomical mode of packing — but that they become 



* A variety of considerations all justify and indeed necessitate the conclu- 

 sion that the hydrogen atom acts uniformly as a univalent or monad radicle. 



t As cerotic acid, CjyHs^Oo, may be obtained by oxidising paraffin wax, it 

 follows that hydrocarbons containing at least 27 atoms of carbon are present 

 in the wax. 



Vol. XIX. (No. 102) 2 b 



