308 



Appendix I. On methods 



Alternative method for filling tonometers. 



On our expeditions on Monte Rosa and in Teneriffe we had not at hand the 

 plant which has been described in the foregoing paragraph. The tonometers were 

 therefore filled over mercury. This method has the merit of simplicity, otherwise 

 I think it is not particularly desirable. The cork is taken out of the tonometer, which 

 is placed with the mouth downwards in a mercury bath. The pressure is reduced 

 inside the tonometer either by means of attaching a pump to the delivery end or by 

 sucking the air out with the mouth. When the tonometer is filled with mercury the tap 

 is shut. A tube from a nitrogen cylinder (or as was the case in Teneriffe, a phosphorus 

 pipette in which nitrogen was made from atmospheric air) w r as then attached to the 

 end of the fine tubing and the tap so turned that the nitrogen ran to waste through 

 the tap. When the dead spaces have all been cleared of air and nitrogen is found to 

 be running- at a convenient rate the tonometer tap is turned through 180 and the 

 mercury replaced by nitrogen. A few bubbles are allowed to escape through the 

 mouth. The tap is then turned back to its former position, the nitrogen tube 

 removed and the gas shut off. The tonometer is corked up, and the oxygen and 

 carbonic acid are added by the method previously described for the addition of ('< > L .. 



To analyse the gas in a tonometer. 



Make ready the gas analysis apparatus by clearing all oxygen out of it and getting 

 the various fluid surfaces to their marks. 



Turn the tap C of the burette as in the figure. Connect the tonometer with the 

 gas burette in the manner indicated in the diagram. Turn the tap C into the vertical 

 position, raise the mercury reservoir till mercury reaches A. Then 

 turn the tap B through 180 and low y er the mercury reservoir till 

 sufficient gas for analysis 8 or 9 c.c. has gone into the gas burette. 

 There is in general a positive pressure in the tonometer so that the 

 surface of the mercury in the gas burette and that in the reservoir 

 will not be the same. This pressure is an essential factor in the ex- 

 periment and must therefore be measured. The simple way of 

 doing this is to place the mercury reservoir as close to the stem of 

 the gas burette as possible and read off the pressure in terms of the 

 number of graduations on the stem. These graduations are, of 

 course, T Jjj of a cubic centimetre, but if it be known how many of 

 them correspond to 1 mm. in height the measurement may readily 

 be expressed in terms of mm. of mercury. In finally calculating 

 the partial pressure of the gases from the percentage composition 

 of the contents of the tonometer, this positive pressure in the tono- 

 meter must of course be added to the height of the barometer. 



When the gas has been transferred to the gas burette, the taps 

 are turned to the positions shown in the figure. The tonometer is 

 removed and the gas in the burette is analysed in the usual way 

 with Haldane's apparatus. 



It may here be helpful to give an actual calculation of the partial 

 pressure of oxygen as obtained from the data at which we may be supposed to have 

 arrived. 



Let the percentage of oxygen in the air of the tonometer be 0, the height of the 



FIG. 151. 



