294 Appendix I. On methods 



desired to spill the permanganate from the reservoir into the bottle. It will ensure 

 the proper spilling of the permanganate. Put on the bottles, the stoppers being 

 efficiently greased with lard or vaseline. Place the apparatus with its bottles in the 

 water bath. 



After five mimites read the meniscus on each side : 



Left Eight 



120 119-5 



Close the taps. See that the meniscus remains constant for two minutes, then 

 remove the apparatus from the bath ; upset the fluid into both bottles. Shake for 

 one minute. Replace the apparatus in the bath. After a minute has elapsed shake 

 again in the air for a minute, put back in the bath and after 60 seconds more read 



Left Eight 



90 159-5 



Difference 69'5 mm. +'.3 = 70 mm. =p. 



Now by calculation 1 c.c. of H 2 2 gives '2 c.c. of O 2 at C. and 760. 



."} o o ^ (" f\ 



.'. it gives "2x r x - at 15 C. and 755= 212 c. or 212 c. mm 



27 o / )o 



.'. &=~ = 3-03. 

 70 



Comparison of this result with another which depends upon the actual measure- 

 ments of the physical constants (i.e. the volumes of the bottles and the bore of the 

 tubing) of the apparatus, shows a slightly higher constant by this method. As 

 a matter of fact very careful research carried out by Burn has shown that this method 

 gives results consistently higher by about 2 % than those given by a method which 

 depends upon the measurement of the sizes of the bottle and tubing. This is scarcely 

 surprising. The old method is of course theoretically accurate ; but for certain 

 small quantities which are negligible and have been neglected in the calculation, 

 the method was mathematically correct. Nevertheless in practice one was dealing 

 with fluids which leave films on whatever they touch, which exert vapour pressures 

 and so forth, and it is not surprising that a theoretical method when checked by 

 a practical one should depart from it to the extent of 2 / . 



To determine the total oxygen capacity of a sample of 

 dejibrinated blood by the differential method. 



Apparatus : a differential blood gas apparatus, a burette, 1 c.c. pipette (calibrated), 

 1 finely drawn out pipette, potassium ferricyanide, ammonia solution (4 c.c. of strong 

 ammonia per litre), vaseline. 



In each blood gas bottle put 2 c.c. of ammonia from the biirette and 1 c.c. of 

 defibrinated blood. Shake up the two together so that the blood becomes thoroughly 

 laked. 



Grease the stoppers with vaseline. 



See that the taps are open. 



With the fine pipette put 0'2 c.c. ferricyanide solution into the reservoir on one 

 side. 



