82 ANAEROBIC ORGANISMS : ISOLATION AND CULTURE 



with a solution of pyrogallate of potash (4 grammes pyrogallic 

 acid in 200 c.c. of 50 per cent, caustic potash solution ; place the 

 pyrogallic acid in the flask, pour in the potash solution by means of 

 a thistle funnel, and stopper immediately), through which the cur- 

 rent of hydrogen is passed to remove any existing traces of oxygen. 

 To avoid accident the three flasks are enclosed in a box as figured, 

 which can be put together by any handy carpenter, and to th( 

 corner of this a two-way tap " e " connected up with the exit tube 

 of flask " c " is attached. 



To start the apparatus, in the first instance, it is only necessaryl 

 to fill the flask " a " up to a little more than two-thirds its capacity! 

 with dilute acid (a 10 or 15 per cent, solution of HgSO^ is recom-J 

 mended in order to obtain pressure by rapid evolution of gas), anc 

 then to blow through the inlet tube"^" until the acid rises well 

 above the layers of zinc in " d." The gas generated by the contact 

 of the acid with the zinc will then issue with a sufficient force b) 

 the two-way tap " e " turned vertically, after bubbling through the 

 pyrogallate of potash solution in flask " c." By placing a pinch-1 

 cock on the tube " d," and keeping open the tap " e " the generation! 

 of gas can be kept up as long as desired, and at once stopped b) 

 reversing the process — i.e. shutting off" the tap " e " and at once 

 opening the inlet tube "^." ^ The pressure of gas will then force the 

 liquid back into the flask " a" and well below the level of the zinc ii 

 flask " b" leaving in the latter a constant reserve of hydrogen under 

 the pressure of the column of liquid in " a ". The process thei 

 becomes automatic — the abstraction of gas from " b " causes descent 

 of the liquid in " a " until the level of the zinc is reached in " b'\ 

 when fresh evolution of gas takes place, the liquid being agaii 

 forced back into the flask " a " as soon as the exit tube or tap ij 

 closed. 



To renew the acid solution without loss of gas it is only neces- 

 sary to close the pinchcock on the connecting tube "/," and syphon 

 out from the flask " a " the solution of sulphate of zinc, replacing it 

 by a fresh acid solution. 



For use with the air or other vacuum pump one way of the tap 

 " e " is joined up with the pump itself by turning the tap horizon- 

 tally, when the pump can be connected up with any desired 

 apparatus by means of a length of pressure tubing as shown. The 



1 To prevent a sudden regurgitation of the liquid from the wash-bottle 

 "c" it is advisable when opening the inlet tube to pinch with the fingers the 

 connecting tube between it and flask "d" for a few moments until the pressure 

 is equalised. 



