Appendix I. On methods 



307 



is gently coming from the cylinder, remove the clamps at B and C. Let the oxygen 

 displace the water backwards into the wash bottle till the required amount has been 

 obtained. Close the clips and disconnect. 



Connect A by rubber tubing to the tap Z, Fig. 147. See that the tap X is 

 closed and that there is no considerable positive pressure in the gas holder by 

 opening \V for a moment. Then with W closed and Z open, transfer the oxygen by 

 blowing into the wash bottle. 



It is now necessary to analyse the gas, by filling a tonometer in the manner 

 described above and analysing the contents with a Haldane's gas analysis apparatus. 

 By the addition of a little air or nitrogen in calculated quantities it is possible to get 

 the gas in the holder pretty exactly to a known composition. It is best however to 

 have the gas with a trifle less oxygen than what is actually likely to be required. 

 For instance if 20 mm. oxygen is being aimed at one would have the gas in the 

 gasometer 19'5 mm. oxygen. One has to analyse the gas in the tonometer before 

 using it ; having made the analysis it is very easy to add a small quantity of air from 

 the gas burette of the Haldane's apparatus. With a 250 c.c. tonometer air is added 

 to the extent of 0'15 c.c. for every tenth of a mm. oxygen pressure required ; of this 

 we shall speak later. 



We now have a mixture of oxygen and nitrogen in the proportions required ; we 

 may want a known pressure of carbonic acid. 



It is not possible to keep carbonic acid in the stock mixture on account of its 

 solubility in the water. It is best to add it from a burette. For this purpose I use 

 a burette of the form shown in figure 150. It is of 15 c.c. 

 capacity and is graduated in c.c. and Yotlis of a c.c., the gas is 

 manipulated over mercury. The tonometer is fixed at A by a 

 junction of rubber pressure tubing. Mercury is run up to the 

 tap of the tonometer, which is shut. The B tap is also shut. 

 The mercury reservoir is now placed so that the surface of the 

 mercury is at the level C. The tap B is opened so as to connect 

 C with the interior. Some excess of C0 2 is forced in by placing 

 the nozzle of a tube connected with the CO 2 cylinder and from 

 which C0 2 is gently coming, in the rubber tube at C. Close the 

 tap. Take away the tube by which the carbonic acid entered. 

 Level the mercury within and without the burette with the tap 

 shut. Then open the tap towards 6', gently raise the mercury 

 reservoir and expel C0 2 to the air until the burette contains the 

 required amount. Shut the tap of the burette. Open the tap 

 of the tonometer, raise the mercury reservoir considerably so 

 that when the tap of the burette is opened towards the tono- 

 meter the CO 2 may go up into the tonometer and not the mercury 

 and blood from the tonometer come down to the burette. Open 

 the tap of the burette towards A and send up the C0 2 into 

 the tonometer. 



It is usual to analyse the gas in the tonometer before using 

 it. If this is to be done remember that some oxygen and car- 

 bonic acid are lost in the analysis and therefore to this extent 

 more of these gases must be put into the tonometer than are to be ultimately 

 required. 



202 



FIG. 150. 



