PRESIDENTIAL ADDRESS. 



17 



Regularities observed on Composition. 



Table III. 



Molecular Values of the Normal Paraffins at their Melting Points. 



Formula 

 of. 



Number of Valencies. 

 [4 for each carbon.] 



Molecular 

 Volume. 



Molecular Vol- 

 ume divided by 



Hydrocarbon. 



[4 for each hydrogen 



Valency Number. 



CnH 2 4 



68 



201-4 



2-962 



C12H26 



74 



219-9 



2-971 



CisH 2 8 



80 



237-3 



2-966 



O14H30 



86 



255-4 



2-970 



C 15 H 32 



92 



273-2 



2-970 



C 16 H 34 



98 



291-2 



2-971 



17 H 36 



104 



309-0 



2-971 



C 1S H3S 



110 



326-9 



2-972 



C 19 H 40 



116 



344-7 



2-971 



C 20 H 42 



122 



362-5 



2-971 



21 H 44 



128 



380-3 



2-971 



C 22 H 46 



134 



398-3 



2-972 



^23 ^48 



140 



416-2 



2-971 



^24^50 



146 



434-1 



2-973 



C27H56 



164 



487-4 



2-972 



^31^64 



188 



558-4 



2-970 



C3 2 H 66 



194 



576-2 



2-970 



^35^72 



212 



629-5 



2-969 



The precision with which an addition of CH 2 to the 

 molecule increases the molecular volume is evident from 

 the constancy of the numbers in the last column. This 

 regularity is, however, not observed in all the properties, 

 and by way of contrast with Table III, Table IV is next 

 given for the melting points of the paraffins. 



The connection between the rise of melting point and 

 addition of OH 2 to the compound is not at first sight at all 

 evident, but by splitting the members of the series into 

 those with an odd and those with an even number of carbon 

 in the molecule, and thus taking the difference of 2 OH 2 

 each time, a somewhat better correspondence is seen 

 between this property and chemical composition. Carrying 

 out the comparison in the case of certain other properties 

 such as the notation of the plane of polarisation, or the 



B-May 5, 1920. . 



