Appendix I. On methods 293 



of oxygen. It must of course when made be accurately titrated and the exact 



quantity of oxygen which it will give off determined. 



The following example may serve to help the experimenter : 



Potass, permanganate solution used, strength being 1 c.c. = '00295 gr. 



Pure 20- volume hydrogen peroxide diluted 100 times, then 100 c.c. H 2 O 2 required 



10'3 c.c. KMn0 4 to set the oxygen free, 



From this equation it is seen that 316 grs. KMnO 4 liberate 160 grs. oxygen. 

 But '0896 x 16 grs. oxygen occupy 1000 c.c. at N.T.P. 



160 x 1000 



Since 100 c.c. hydrogen peroxide contain oxygen liberated by 10'3 c.c. KMn04, 



1 "5x1 0-3 



* 



1 O C.C. 



,, ,, 



1-5 x 10-3 x -00295 

 which contain - - grs. KMn0 4 . 



,, 160x1000 



Then 316 grs. KMn0 4 liberate - c.c. 2 . 



' x lo 



1-5 xl 0-3 x -00295 l'5x 10'3 X "00295 X 160 x 1000 



100 100X '0896x16x316 



= 1537 c.c. 2 . 



Temp, was 13'4 C., pressure 755 mm. 



Now 1000 c.c. air, saturated with water vapour at this temp, and press., occupy 



932 c.c. at N.T.P. 



153'7 

 .'. vol. of O 2 actually liberated was cub. mm. 



Difference of press, observed was 46'2 mm. 



But vol. in bottle was 3'5 c.c. which would add "35 to the constant 



.'. Constant for empty bottle = 3'92. 



Perhaps the greatest drawback in this method is due to the difficulty of obtain 

 ing pure hydrogen peroxide. The commercial reagent is made up with glycerine or 

 other substances which are added for the purpose of preventing the H 2 2 from 

 deteriorating in strength. Such peroxide appears to give unreliable results. 



The calibration of the apparatus is carried out as follows : 



Into each of the bottles put 1 c.c. of H 2 O 2 and 2 c.c. of H 2 S0 4 strength N/100. 



If the left bottle is the one which is to have its constant determined, place "2 c.c. 

 of permanganate in the reservoir and the same quantity of water in the correspond- 

 ing reservoir of the other side. After the permanganate is in its place cut a piece 

 of filter paper 2 or 3 cm. in length and 1 mm. in breadth and place it so that it projects 

 a little from the reservoir but does not become wet with the permanganate, till it is 



* This was volume of H 2 2 put in blood gas bottle. 



