, provided with a copper or gun-metal lid, which
is secured in place by means of bolts and thumbscrews, the joint between
the cylinder and its lid being hermetically sealed by the interposition
of a rubber washer. The cover is perforated for a branched tube carrying
a vent cock, a manometer, and a safety valve. The copper boiler is
mounted in the upper half of a cylindrical sheet-iron case--two
concentric circular rows of Bunsen burners, each circle having an
independent gas-supply, occupying the lower half. In the interior of the
boiler is a large movable wire basket, mounted on legs, for the reception
of the articles to be sterilised.

TO USE THE AUTOCLAVE.--

1. Pack the articles to be sterilised in the wire basket.

2. Run water into the boiler to the level of the bottom of the basket;
also fill the contained flasks and tubes with water.

3. See that the rubber washer is in position, then replace the cover and
fasten it tightly on to the autoclave by means of the thumbscrews.

4. Open the vent cock and light both rings of burners.

5. When steam is issuing in a steady, continuous stream from the vent
tube, shut off the vent cock and extinguish the outer ring of gas
burners.

6. Wait until the index of the manometer records a temperature of 120 deg.
C., then regulate the gas and the spring safety valve in such a manner
that this temperature is just maintained, and leave it thus for twenty
minutes. In the more expensive patterns of autoclave this regulation of
the safety valve is carried out automatically, the manometer being
fitted with an adjustable pointer which can be set to any required
pressure-temperature and so arranged that when the index of the
manometer coincides with the adjustable hand the safety valve is opened.

7. Extinguish the gas and allow the manometer index to fall to zero.

[Illustration: FIG. 30.--Chamberland's Autoclave.]

8. Now open the vent cock slowly, and allow the internal pressure to
adjust itself to that of the atmosphere.

9. Remove the cover and take out the sterilised contents.

~Sterilisation Periods.~--An exceedingly useful device for the timing of
sterilisation periods (and indeed for many other operations in the
laboratory) is the

ELECTRIC SIGNAL TIMING CLOCK.

This is a clock of American type in which the face is surrounded by a
metal plate having a series of 60 holes at equal distances apart,
corresponding to the minutes on the dial. This plate is connected