NUTRIENT JELLY— EXAMINATION OF AIR. 



91 



is now introduced into the cylindrical tube, sufficient to make a thin 

 layer along its floor. The tube leading from the cylinder is clamped, 

 and the pore in the indiarubber sheeting is covered with a cap of 

 sterilised cotton wool. The glass cylinder and its contents are then 

 steamed for thirty minutes on each of two consecutive days, to ensure 

 their sterility, the cylinder being kept level during this process. On 



Fig. 47. — Hesse's apparatus for determining relative purity of 

 atmospheres (qualitative and quantitative). 



a. Hollow glass cylinder, with {b) perforated indiarubber 



sheeting. 

 I. Exhausting apparatus, with siphon action. 



cooling, the jelly sets in a thin layer on the lower aspect of the cylindri- 

 cal glass tube. In performing the experiment, the litre flasks, which are 

 filled with water, are put in communication with one another, and with 



