52 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Examination of a Commercial Specimen of Hydrocarbons by 

 Fractional Distillation. 



On distilling 50-100 c.c. of ligroin or kerosene from a small dis- 

 tilling flask attached to a condenser and observing the temperature 

 indicated by the thermometer, it will be seen that the temperature never 

 remains constant for any length of time. The substance is a mixture. 

 Several fractions which boil within 10 or 20 ranges of temperature 

 can be collected in separate receivers. By redistilling these fractions 

 and using a fractionating column (cf. p. 9) a pure product with a 

 constant boiling-point can eventually be obtained. 



Properties. 



The saturated hydrocarbons have a peculiar odour. They are in- 

 soluble in water, but are soluble in alcohol, ether and other organic 

 liquids. 



Inflammability. 



Marsh gas and the other gases burn with a non-luminous flame and 

 form explosive mixtures when mixed with a certain proportion of 

 oxygen or air. 



'f he lower members amongst the liquids are also inflammable and 

 burn with a more or less luminous flame. E.g. if about 3 c.c. of 

 ligroin be placed in a watch glass and a lighted match applied it will 

 burn. 



The higher liquid members do not burn until they have been 

 warmed. E.g. on applying a lighted match to about 3 c.c. of kerosene 

 contained in a watch glass, the flame is extinguished, but if the kerosene 

 be warmed on the water-bath to about 40 and a lighted match again 

 applied, the vapours of the kerosene will be ignited. 



In a lamp the kerosene rises to the surface of the wick by capil- 

 larity, and on applying a light the oil becomes hot and turns into 

 inflammable vapour. 



Inertness towards Chemical Reagents. 



The saturated hydrocarbons are very inert substances ; they are not 

 acted upon by concentrated acids or alkalies except under special 

 conditions, and on account of their stability they are known as the 

 paraffins horn flarum affinis, little affinity. 



E.g. on shaking about I c.c. of ligroin or kerosene with 



(a) concentrated sulphuric acid, 



(f) concentrated nitric acid, 



(r) potassium permanganate solution, 

 d bromine dissolved in chloroform, 



