Rubber bands make the joints air-tight.
[Illustration: FIG. 193.--Vertical section of purifier.]
The base is stood bottom upwards in a larger tin containing an inch and a
half of water. The water acts as a seal, preventing the passage of the gas
from one compartment to another through the pipes which it traverses, in
the order indicated by the arrows and numbers in Fig. 192, to reach the
outlet. On its way the gas is deprived of any water and of any traces of
tar. The condensed water and tar fall from the open ends of the pipes into
the base.
The Purifier is made of a large tin with overlapping lid. Near the bottom
is soldered on an inlet pipe; just below the lid an outlet pipe. Cut out
two discs of perforated zinc or sheet tin to fit inside the tin easily, but
not loosely. (If tin is used, make a number of small holes in it.) The
lower of the discs (Fig. 193, Bl) has three wire legs, AA, soldered to it,
to support the upper disc, B. Three short supports keep it clear of the
bottom.
The tin must be charged with a mixture of two parts green sulphate of iron
and one part lime.
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