AGf~ICULTURAL RESEARCH, PUSA.

CUI/l'IFA'l'ION OJ!' lI11CRO-OIWANISMS 13U
jar. This indicator, when in the jar, should remain
colourless except for a slight tinge of blue at the top,
which slowly disappears during the passing of the
current.
The lid is clamped down and the jar connected to
a hydrogen supply. The current is turned Oll so that
the palladinised asbestos may be heated. The combination
of oxygen and hydrogen takes place quietly
in the jar. Water is formed, and more hydrogen enters
to take the place of the oxygen consumed. After
about twenty minutes all the oxygen is used up, and
the tap is then turned off and the hydrogen supply
disconnected. The jar is placed in the incubator, and
within a few hours the indicator tube containing
the methylene blue should be colourless, showing that
complete anaerobiosis is established.
In spitc of the wil'e gauze rouwl the palladilliscd
asbestos, explosions sometimes occur, and it is advisable
always to place the unuerobie jar, il.' made or
glass, inside a box while the curl'ent is passing through
the spool.
HYDROGEN SUPPLY
A hydrogen supply may be obtftined from a Kipp's nppmatus
by the action of sulphuric acid on zinc. Thc glls must bc
purified by passing through three wash-bottles: (1) containing
a tcn pel' ecnt. solution of lead acetate, to remove sulphuretted
hydrogen; (2) containing a ten per cent. solution of silvcr
nitrate, to absorb arseniuretted hydrogen; and (3) containing [t
mixture of pyrogallie acid and caustic soda, to remove oxygen.
It is more convenient, however, to obtain hydrogen from
a cylinder containing thc compressed gas. The commercial
hydrogen so obtained is suitable for usc in the varions anaerobic
apparatus employed. The hydrogen cylinder eaullot
be cOllneetecl directly to the McIntosh and Fildes' jar, as the
pressure is too gl'ellt. By the following apparatus, however,
the amount of hydrogen entering the jar can be measured,
and its pressure controlled.
Hydrogen from the cylindcr is passed through the washhottle
A, the rate of' flow bcing estimated by the bubbles of
gas rising through the water. From this thc gas passes through
the three-way stopcock B to a large jar C filled with water.
This jar should have a capacity of 15-20 litres, and may be