aced by hydrogen. This is determined by
collecting some of the gas which bubbles through the water in the basin
in a test-tube and testing it by means of a lighted taper.

7. Close the metal clip on the tube through which the gas is entering;
close the clip on the exit tube.

8. Disconnect the gas apparatus.

9. Incubate.

~Method X~ (Botkin's Method).--

~Apparatus Required.~--

Large glass dish 20 cm. diameter and 8 cm. deep. Flat leaden
cross slightly shorter than the internal diameter of the glass dish.
Bell glass about 15 cm. diameter and 20 to 25 cm. high.
Metal frame for plate cultivations.
_Or_, glass battery jar for tube cultivations.
Cylinder of compressed hydrogen.
Rubber tubing.
Two pieces of ~U~-shaped glass tubing (each arm 8 cm. in length).
Half a litre of glycerine (or metallic mercury).

METHOD.--

1. Place the leaden cross inside the glass dish, resting on the bottom.

2. Prepare the cultivations in the usual way.

3. Place the tube cultivations in a glass battery jar (or the plate
cultivations on a metal frame), resting on the centre of the leaden
cross.

4. Cover the cultivations with the bell jar.

5. Adjust the U-shaped pieces of glass tubing in a vertical position on
opposite sides of the bell jar, one arm of each inside the jar, the
other outside. These tubes are best held in position by embedding the
U-shaped bends in two lumps of plasterine stuck on the bottom of the
glass dish. Fix a short length of rubber tubing clamped with a metal
clip to each of the outside arms (Fig. 134).

6. Fill the glass dish with glycerine or metallic mercury to a depth of
about 5 cm.

[Illustration: FIG. 134.--Botkin's apparatus.]

7. Connect up one U-shaped tube with the hydrogen cylinder (or gas
apparatus) by means of rubber tubing. Replace the atmospheric air by
hydrogen, as in method IX.

8. Clamp the tubes and disconnect the gas apparatus.

9. Incubate.

~Method XI~ (Novy's Method).--

~Apparatus Required.~--

Jar for plate cultivations (Fig. 135).
_Or_, jar for tube cultivations (Fig. 136).
Lubricant for stopper of jar.
Rubber tubing.
Cylinder of compressed hydrogen.

METHOD.--

1. Prepare cultivations in the usual way.

2. Place these inside the jar.

3. Lubricate the stopper and insert it in the mouth of the jar, with the
handle in a line with the two side tubes.

4. Connect up the delivery tube a with the hydr