174 Proceedings of Indiana Academy of Science 
At the reversal point a concentration of 5.6 per cent calculated as NO 
was obtained, while at the point b after the pressure had become con- 
stant concentration of only 0.6 per cent NO was found. Spiel con- 
cludes that no lower oxides of nitrogen are formed, only N:.0;. Spiel 
determined the concentration at the reversal point by making a second 
run holding all the conditions as near like the first run as possible. 
It has been found, however, by plotting the data which Spiel gives, 
that the pressure time characteristic was not the same for both runs, 
and this condition is one which the author of this paper has found to 
exist in all the work done at Purdue with enclosed volumes of air. 
Characteristics, different from anything reported by Spiel, appeared 
when the first run was made on the discharge tube, after being set 
up, using the induction coil for power supply. The changes in current 
and pressure with time may be seen by reference to Fig. 3. The cur- 
rent shown is the actual current and was measured in the ground 
connection of the cooling tank. The full line curve marked D-2 repre- 
sents the first run, which was continued for 205 minutes. The pres- 
sure seemed to go through a cyclic change which also appeared in the 
current to some extent. A second run (D-3) was made, giving quite 
different current with a reversal at a higher pressure coming 20 min- 
Using Duplicate of Spiels Tube 
Alternating Current. 
60 cycles. 
oltge Consta 
Milli-amperes, 
a= 
a 
ea 
Time in Minvtes, 
Fig. 7. 
