338 



Scientific Proceedings, Royal Dublin Society. 



reduced from — t^ to -^rx, a correction for this must be applied. The pressure 

 50 50 



in the vessel before the experiments was 768-1 mm., and at the end was 

 758-0 mm. 



Taking the composition of atmospheric air to be approximately : nitrogen, 

 79 per cent., oxygen, 21 per cent., and the coefficient of absorption of oxygen 

 as 0-0;310 at 20° C, we can calculate the amounts of oxygen in solution at 

 the beginning and at the end of the experiments. 



The pressure of aqueous vapour at 20-0° C. is 17-5 mm. 



The volume of oxygen in solution at the start is — 



7^0 = -0310 X 110 x^ x^ = -706c.c. 



The volume in solution at the end is- 

 Fi = -0310 X 110 X ^ 



740-5 



= -598 c.c. 



50 760 



Hence the difference due to change in the saturation value is -108 c.c, 

 and this, when added to the volume indicated by the manometer reading, 

 gives a total of 1'62 c.c. as the actual absorption. 



The 10 c.c. of ferrous sulphate used should have absorbed 1-64 c.c. oxygen 

 according to its titre by potassium permanganate, hence the two values agree 

 within 1\ per cent. 



I-5I2 



O IZ60 



« 756 



•252 



40 



SO 60 



Time in Minutes 



90 



100 



Fig. 3. 



The graph, fig. 3, shows the course of the absorption. During the 

 first part of the absorption the water is completely de-aerated by the excess 



