246 METHODS OF CULTIVATION 



Pyrogallic acid tablets. 

 Cylinder of compressed hydrogen. 

 Geryk or other air pump. 

 Rubber pressure tubing. 

 10 c.c. pipette. 

 Glass tubing. 



Dry granulated caustic soda or compressed tablets each con- 

 taining 0.4 grammes sodic hydroxide. 

 Small beaker of water. 



METHOD. 



1. Prepare the cultivations in the usual way. 



2. Place the glass dish in the centre of the glass 

 slab, and stand the cultivations inside this. 



3. Place a sufficient number of pyrogallic acid 

 tablets at one side of the glass dish (i. e., i tablet for 

 each 100 cubic centimeters air capacity of the bell jar). 

 Place a small heap of dry granulated soda (or half a 

 dozen tablets of sodic hydroxide) by the side of the 

 pyro tablets. 



4. Smear the flange of the bell jar with resin oint- 

 ment and apply the jar firmly to the glass slab, covering 

 the cultivations so arranged that the long tube passes 

 with its lower end into the glass dish at a point directly 

 opposite to the pyrogallic acid tablets. Lubricate the 

 two stop-cocks with resin ointment (Fig. 137). 



5. Connect up the short tube a with the gas-supply 

 by means of rubber pressure tubing and open both stop- 

 cocks. 



6. Connect a long, straight piece of glass tubing to 

 the long tube b by means of a piece of rubber tubing 

 interposing a screw clamp : and collect samples of the 

 issuing gas from time to time and test. 



7. When the air is displaced, shut off the stop-cock 

 of the entry tube, then that of the exit tube b. Screw 

 down the clamp and remove the glass tube from the 

 rubber connection and connect up the short tube a to 

 the air pump by means of pressure tubing. 



8. Open the stop-cock of tube a and with two or three 



