Structure of Simpler Organic Compounds. 53 



sible number of isomerides. In the case of the paraffins 

 with four carbon atoms, two isomerides exist, whereas in 

 the case of these with five carbon atoms, three exist. 

 When the formula reaches the complexity C 13 H 28 , it has 

 been calculated that no less than 802 isomerides can exist. 



THE PARAFFIN HYDROCARBONS. 



A whole series of compounds is known, the composi- 

 tion of which may be represented by the general formula 

 C n H 2n+2 . These substances are found in large quantities 

 in nature in petroleum or mineral naphtha. The lower 

 members of the series are gaseous under ordinary atmos- 

 pheric conditions of temperature and pressure, and can 

 only be liquefied under high pressures and at low tem- 

 peratures. The boiling points rise as the molecular 

 complexity increases, and the highest members of the 

 series are solid at ordinary temperatures (paraffin wax and 

 ozokerite). It is difficult to separate the pure chemical 

 individuals from the various natural oils which consist of 

 a mixture of a large number of them. By a process of 

 fractional distillation the crude oils can be separated into 

 fractions to which various trade names are assigned. The 

 gases can be collected separately as they issue from the 

 earth and used for burning; the lower boiling liquid 

 fractions are used for motor spirit, and are largely em- 

 ployed as solvents in the laboratory under the names of 

 " light petroleum," " ligroin," " petroleum ether," etc. ; a 

 higher boiling liquid fraction is known as " kerosene," the 

 fraction which is partly solid at ordinary temperature 

 is known as " vaseline," whereas the fractions containing 

 the highest hydrocarbons constitute the paraffin waxes, 

 from which products of varying melting points can be 

 obtained. 



