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- Apparatus for the Preparation of Hydrogen. In the laboratory, small quantities of hydrogen may
be generated in the simple apparatus shown in Fig. 14. Zinc and
some water are placed in the generating flask, and dilute sulfuric
acid* is added in portions through the thistle tube.
-
- * As sulfuric acid is heavier than water
(sp. gr. 1.84) and much heat is generated on its dilution, it
should always be poured slowly into water and should never be
diluted by pouring water upon the acid. Pouring water on concentrated
sulfuric acid may cause an explosion.
-
 A more convenient apparatus
for the preparation of larger amounts, or when it is desired
to have the gas always ready for use, is the Kipp generator (Fig.
15).  The zinc is placed in the
middle bulb and the dilute acid is poured in through the upper
bulb, which communicates with the lower one through the tube
A. When the stopcock B is opened, the acid rises
and comes in contact with the zinc in the middle bulb and the
generation of hydrogen begins. Whenever the stopcock is closed
the hydrogen generated forces the acid away from the zinc and
the action ceases as soon as the acid moistening the surface
of the zinc is exhausted. The generator is not altogether satisfactory
because the spent acid containing zinc sulfate is mixed with
that which has not been used, diluting it and causing the action
to become very slow before the acid has been exhausted.
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