142 Knight and Priestley. — The Respiration if Plants 
i. Experiments with Small Direct Currents at Low Voltages. 
In these experiments the respiration chamber was a glass tube about 
30 cm. long and 3-5 cm. in diameter, with rubber stoppers at both ends 
fitted with two delivery-tubes. The current was applied at first through 
unpolarizable electrodes (Detmer, loc. cit, p. 157), but these were later 
replaced by simple mercury-platinum contact electrodes, as with these it 
was found that very little progressive reduction in current strength took 
place. Contact was ensured by shaking the seeds well together before 
inserting the rubber stoppers. Current strength was measured by a 
calibrated Paul millivoltmeter, shunted when necessary. In the later 
experiments a thermometer bulb was introduced through a side tube into 
the respiration chamber (see Fig. 2). 
In all experiments the temperature was kept constant as far as possible, 
but slight variations were unavoidable. When these occurred, the carbon 
dioxide figure was corrected on the basis of the Van ’t Hoff law for chemical 
reactions, a rise of io° C. being considered to produce an increase of 
100 per cent., all values being reduced to the temperature at which the first 
estimation was made. F. F. Blackman 1 showed that respiration approxi- 
mately followed this law, and we found that a control-curve obtained under 
varying temperature conditions, when corrected in this manner, became 
identical in form with the curve obtained from respiration at constant 
temperature. 
Peas were used in the direct-current experiments, and the control- 
curve was of the form shown in Fig. 3 (see also Table I). 
For the sake of simplicity, a few typical results are introduced into the 
Report of British Association, Dublin, 1908, p. 896. 
