306 



Appendix I. On methods 



At one end the main connects with a glass tap (Fig. 148) A, and beyond this 

 there is a Geryk pump. At the other end there is a T-tube C, a vacuum gauge Z>, 

 and a glass tap. 



A B 



TG TT 



FIG. 148. 



To fill a tonometer with gas from one of the gas holders say the one attached to 

 the tap G. Place the tonometer, which is of course securely corked, on the T-tube (.', 

 open the tap /' of the tonometer, close all the other taps except A. Turn the Geryk 

 pump until the gauge shows a good vacuum. Then close A and gently open G. If 

 G be opened suddenly the gauge may be broken. Close G, open A exhaust once 

 more, close A, open G and after a minute or so close G again. Close /'and take off 

 the tonometer. 



The holders may be filled with nitrogen through the tap at the bottom of bottle 

 B, Fig. 146, from a nitrogen cylinder. This is done with the bottle full of water and 

 just enough water in A to cover the tap at the bottom. The water is then displaced 

 upwards into the bottle A by the nitrogen the nitrogen must not be run in too 

 rapidly or some part of the apparatus may blow out. 



,B 



' Fio. 149. 



To obtain a given oxygen pressure add 20 c.c. of oxygen for each mm. required. 

 The oxygen may be transferred from an oxygen cylinder in an apparatus consisting 

 of a 250 c.c. graduated measuring cylinder fitted with a rubber cork and with glass 

 tubing after the manner of a wash bottle. This is attached to a wash bottle of about 

 a litre capacity, the attachment being as shown in the figure. Start with the whole 

 measuring cylinder and tubing connected with it full of water, and the wash bottle 

 partly full. Place the glass tube A on a piece of rubber tubing along which oxygen 



