144 



Mr. F. Kidd. 



the mean concentration of C0 2 between the initial and final concentrations- 

 for any period between two analyses is taken as the effective pressure 

 influencing COa production during that period. This figure enables one to 

 read values for CO2 production corresponding to any concentrations of C0 2 . 



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Fig. 1. — The retarding effect of carbon dioxide upon anaerobic C0 3 production, and_the- 

 recovery after the removal of C0 2 concentrations. (See Table IV.) 



1, 2, 3, 4 — Total C0 2 production while under influence of C0 2 concentrations-after 19,. 

 31, 51, 90 hours respectively. 



5 — Total C0 2 production during 47 hours after removal of C0 2 concentrations. 

 A, B, C, D, E — Series of readings from five parallel experiments. 



It is important to know how far the action of CO2 upon anaerobic 

 C0 2 production in these experiments is a constant retarding effect, and not 

 merely confined to the first few hours. In fig. 2 the same results (Table IV) 

 are given in different form, the total CO2 evolved being plotted against time 

 for two concentrations of CO2, and 20 per cent, (the A r alues for these 

 constant concentrations being taken from fig. 1). From these curves the 

 curves for rate of CO2 production plotted against time are deduced, and show 

 at once that the depressant action of CO2 is a continuous effect. In this case 

 the average depressant effect of C0 2 during the whole 90 hours of experi- 

 ments is 0"6, taking the control as 1. Both the first and the second 45 hours 



