tinder Various Electrical Conditions. 147 
them from reaching the living material. A small vessel of turpentine was 
introduced into the respiration chamber above the peas, which was found to 
be effective in absorbing the toxic gases. (See later experiments as to the 
effect of gases on seedlings.) 
Since turpentine was used in many of the experiments, it became 
necessary to carry out controls with it, to ascertain its effect, if any, upon 
respiration. Accordingly the respiration curve was determined for peas 
separated by glass wool as in 2, with a vessel of turpentine in the respiration 
chamber, discharge not being applied. 
The curve was found to coincide with the normal, the small amount of 
turpentine vapour which was unavoidably present in the atmosphere having 
no effect upon respiration (Table V). 
4. The possibility of the decomposition ol the turpentine by the dis- 
charge was next considered, and it was realized that if this took place, an 
evolution of carbon dioxide was a conceivable consequence, this being 
naturally undesirable, since carbon dioxide output was taken as a criterion 
of respiration. 
To test this, a vessel of turpentine was placed in the respiration 
chamber, no seeds being present, and the discharge switched on, a stream 
of air being drawn through the whole apparatus as described above. 
Analysis of the baryta solution in the Pettenkofer tube showed that no 
carbon dioxide had been evolved (Table VI). 
Having completed these controls, full results of which will be found in 
the Appendix, experiments upon the effect of electrification upon the seeds 
were proceeded with. 
When a platinum-mercury contact electrode was used to apply the 
discharge, it was found that under the conditions of experiment the current 
produced was very much in excess of that used in the field trials, and since 
our experiments were intended to be comparable with those trials, it was 
thought expedient to employ currents of the same order of magnitude. In 
order to cut down the voltage available with our apparatus, the following device 
was adopted and found effective. The tube of the electrode (see Fig. 1) 
was filled with xylol instead of mercury, and the cable from the high 
tension installation rested in the xylol, which completed the contact with 
the platinum discharge point. By varying the length of the column of 
xylol between the ends of cable and platinum points, and thereby varying 
the resistance, it was possible to vary the current passing from the discharge 
point. 1 
When, however, this distance was below about 1 centimetre, a new 
factor became evident in the passing of sparks between the end of the cable 
and the platinum wire. The heat produced caused the xylol finally to boil, 
and it became necessary to switch off the discharge. Another disadvantage 
1 See N. R. Campbell, Phil. Mag., Ser. vi, vol. 22, p. 301, Appendix to paper on Delta Rays. 
