To purify the oil it is placed in a large metal vessel or
"still". Steam is first passed over the oil in the still, and
this changes the lightest of the oils into vapours. These
vapours are sent through a series of pipes surrounded with cold
water, where they are cooled and become liquid again. Petrol is
a mixture of these lighter products of the oil.

If petrol be placed in the air it readily turns into a vapour,
and this vapour is extremely inflammable. For this reason petrol
is always kept in sealed tins, and very large quantities are not
allowed to be stored near large towns. The greatest care has to
be exercised in the use of this "unsafe" spirit. For example, it
is most dangerous to smoke when filling a tank with petrol, or to
use the spirit near a naked light. Many motor-cars have been set
on fire through the petrol leaking out of the tank in which it is
carried.

The tank which contains the petrol is placed under one of the
seats of the motor-car, or at the rear; if in use on a
motor-cycle it is arranged along the top bar of the frame, just
in front of the driver. This tank is connected to the
"carburettor", a little vessel having a small nozzle projecting
upwards in its centre. The petrol trickles from the tank into
the carburettor, and is kept at a constant level by means of a
float which acts in a very similar way to the ballcock of a water
cistern.

The carburettor is connected to the cylinder of the engine by
another pipe, and there is valve which is opened by the engine