468 BACTERIOLOGICAL ANALYSES 



EXAMINATION OF AIR. 



Quantitative. 



Apparatus Required: 



Aspirator bottle, 10 litres capacity, fitted with a delivery tube, 

 and having its mouth closed by a perforated rubber stopper, 

 through which passes a short length of glass tubing. 



Erlenmeyer flask, 250 c.c. capacity (having a wide mouth 

 properly plugged with wool), containing 50 c.c. sterile water. 



Rubber stopper to fit the mouth of the flask, perforated with 

 two holes, and fitted as follows: 



Take a 9 cm. length of glass tubing and bend up 3 cm. at 

 one end at right angles to the main length of tubing. Pass 

 the long arm of the angle through one of the perforations in the 

 stopper; plug the open end of the short arm with cotton- wool. 



Take a glass funnel 5 or 6 cm. in diameter with a stem 12 

 cm. in length and bend the stem close up to the apex of the 

 funnel, in a gentle curve through a quarter of a circle; pass the 

 long stem through the other perforation in the rubber stopper. 



A battery jar or a small water-bath to hold the Erlenmeyer 

 flask when packed round with ice. 



Supply of broken ice. 



Rubber tubing. 



Screw clamps and spring clips, for tubing. 



Water steriliser. 



Retort stand and clamps. 



Apparatus for plating (as for enumeration of water organisms, 

 vide page 420). 



METHOD. 



1. Fill 10 litres of water into the aspirating bottle 

 and attach a piece of rubber tubing with a screw clamp 

 to the delivery tube. Open the taps fully and regulate 

 the screw clamp, by actual experiment, so that the tube 

 delivers i c.c. of water every second. The screw clamp 

 is not touched again during the experiment. 



At this rate the aspirator bottle will empty itself 

 in just under three hours. Shut off the tap and make 

 up the contents of the aspirator bottle to 10 litres again. 



2. Sterilise the fitted rubber cork, with its funnel 

 and tubing, by boiling in the water steriliser for ten 

 minutes. 



