e noted are as efficient as the
Chamberland candles and filter rather more rapidly.

_Apparatus Required._--

1. Separatory funnel containing the unfiltered fluid.

2. Sterile filter candle (Fig. 34), the open end fitted with a rubber
stopper (Fig. 34, a) perforated to receive the delivery tube of the
separatory funnel, and its neck passed through a large rubber washer
(Fig. 34, b) which fits the mouth of the filter flask.

3. Sterile filter flask of suitable size, for the reception of the
filtered fluid, its mouth closed by a cotton-wool plug.

4. Water injector Sprengel (see Fig. 38, c) pump, or Geryk's pump (an
air pump on the hydraulic principle, sealed by means of low
vapor-tension oil, Fig. 35).

If this latter is employed, a Wulff's bottle, fitted as a wash-bottle
and containing sulphuric acid, must be interposed between the filter
flask and the pump, in order to prevent moist air reaching the oil in
the pump.

5. Air filter (_vide_ page 40) sterilised.

6. Pressure tubing.

7. Screw clamps (Fig. 36).

METHOD.--

1. Couple the exhaust pipe of the suction pump with the lateral tube of
the filter flask (first removing the cotton-wool plug from this latter),
by means of pressure tubing, interposing, if necessary, the wash-bottle
of sulphuric acid.

[Illustration: FIG. 34.--Porcelain filter candle.]

[Illustration: FIG. 35.--Geryk air pump.]

2. Remove the cotton-wool plug from the neck of the filter flask and
adjust the porcelain candle in its place.

[Illustration: FIG. 36.--Screw clamps.]

3. Attach the nozzle of the separatory funnel to the filter candle by
means of the perforated rubber stopper (Fig. 37).

[Illustration: FIG. 37.--Apparatus arranged for filtering--aspiration.]

4. Open the tap of the funnel, and exhaust the air from the filter flask
and wash-bottle; maintain the vacuum until the filtration is complete.

5. When the filtration is completed close the tap of the funnel; adjust
a screw clamp to the pressure tubing attached to the lateral branch of
the filter flask; screw it up tightly, and disconnect the acid
wash-bottle.

6. Attach the air filter to the open end of the pressure tubing; open
the screw clamp gradually, and allow filtered air to enter the flask, to
abolish the negative pressure.

7. Detach the rubber tubing from the lateral branch of the flask, flame
the end of the branch in the Bunsen, and plug its orifice with sterile
cotton-wool.

8. Remove the filter