VACUUM TUBE CIRCUITS AS SOURCE OF POWER 201 
The frequency of the current was found to increase by decreas- 
ing the capacity of the condenser, decreasing the inductance Eg, 
increasing the inductance Li and as the filament current ap- 
proaches the most favorable value for the filament. 
Several makes of vacuum tubes were used. Only those where 
the plate is very close to the filament gave oscillations. 
SUMMARY 
The vacuum tube circuit shown in figure 36 will produce an 
oscillating current of sufficient frequency for conductivity meas- 
urements. 
The advantages of the apparatus are : 
1. The elimination of the noise accompanying mechanically 
produced oscillations. 
2. The elimination of the heat developed by the mercury rec- 
tifier. 
3. The simplicity of the apparatus. 
The disadvantages of the apparatus are: 
1. The changes of frequency due to external capacities and 
changes in the filament current. 
2. The small current obtained by using the ordinary vacuum 
tube. 
The work is being continued with the hope that the strength 
of the current can be increased. 
In conclusion the authors wish to thank Dr. John L. Tilton 
whose cooperation made possible this work. 
Chemical Laboratory, 
Simpson College. 
