Appendix I. On methods 301 



(5) That the shape of the bottles be such that when hanging on the apparatus 

 with the manometer vertical 0'02 c.c. fluid placed in the pouch at -X" has no tendency 

 to find its way down the tubing to Y. 



(6) That the diameter A A of the bottle be such that if 0'2 c.c. of ammonia 

 and O'l c.c. of blood be placed at Y the fluid will assume the position shown in 

 Fig. 142 when the bottle is placed in that position. If A A is too narrow the 

 fluid sticks in the bottom part of the bottle even when the latter is placed on 

 its back. 



Calibration of the differential apparatus for analysis of 

 oxygen in 0*1 c.c. of blood. 



Two methods are available for this calibration. 



(i) A direct comparison of the oxygen given out by blood with that given out by 

 the same blood in the larger form of apparatus, the constant of which is known. 



(ii) The hydrogen peroxide method. The strengths of solutions necessary and 

 their standardisation are carried out in the small as in the case of the larger apparatus 

 already described. The only point which needs amplification is the use of the solu- 

 tions in the small apparatus. This is very simple. Into each bottle is placed 0'2 c.c. 

 of N/100 sulphuric acid and O'l c.c. of standard hydrogen peroxide. 



FIG. 143. 



These should be run into the bottles from a pipette with a long narrow end, so 

 that the sides of the bottle are not wet. For putting the potassium permanganate 

 into the bottle a special pipette is necessary. It is drawn out and bent at the end. 

 As shown in the figure it may be used to place the permanganate in the pouch. 



The danger, of course, is that the H 2 O 2 and the permanganate may become 

 prematurely mixed. If the bottle is of the proper shape and reasonable care is taken, 

 this danger should not cause serious preoccupation. The other bottle is filled in the 

 same way except that water, not permanganate a drop in each case is placed in 

 the pouch. 



The bottles are then placed on the apparatus which has, of course, been adequately 

 greased. Care must be taken to see that the taps are open when the bottles are put on. 



The apparatus is placed in the bath and allowed to stand for five minutes the 

 meniscus is read, the taps are closed, if in another minute the meniscus has not changed 

 the bottles may be shaken. Care being taken that both the permanganate and the 

 water become mixed with the acid hydrogen peroxide. 



The bottles are then shaken and left in the bath for alternate minutes until 

 constant readings are obtained. 



The method of working out the constant is similar to that already given for the 

 larger apparatus. Suppose k to be '38. 



