178 Proceedings of Indiana Academy of Science 
eee 4 Using Duplicate of Spicls Tube. 
3 Alternating Current 
= = ( 
3 ; 31 cycles, 
x J 
bel 
5 =| 
penal 
159 0 
Nd 
gaia 
HES 
nes 
2 +%0 
ae 
ee Ne ae e 0 
Time in Minvtes 
Feg.- 6. 
° 10 Ea 30 40 fo oo 70 Bo 30 
paper was constructed. The first test on this tube was made with 
alternating current and the results may be seen by reference to Fig. 7. 
The pressure characteristic is very different than any obtained with 
the first tube. Instead of decreasing rapidly as before, the pressure 
remained constant for 10 minutes and then began to fall rapidly. For 
the most part, the points fall on a straight line, which again is very 
different from any result obtained before. The pressure decreased 114 
mm. in 190 minutes, which when corrected for temperature gives a 
pressure decrease of 143 mm. below the atmosphere. This represents 
a contraction in volume of nearly one-fifth and yet the NO concen- 
tration was only 1.2 per cent, and only a slight odor of ozone. It ap- 
pears likely that some heavier molecule than we know of at present 
is being formed. That this must be true will be clear when it is stated 
that in order to secure such a pressure decrease an NO concentration 
of 15 per cent would be required if the decrease was due to the forma- 
tion of N.O; caleulated as NO. Such a contraction is not of the same 
order of magnitude as the one observed in this run. 
Several runs were made on this tube in an effort to again secure 
the great pressure decrease observed in D-37, but although most of the 
runs showed the same initial characteristic as did D-37, yet reversal 
came in every case before the pressure had decreased more than 60 
mm. The difficulty of duplication of results is one which has been 
met with continually in the work done on these discharge tubes. 
CONCLUSIONS DRAWN FROM THE TESTS. 
1. Holding conditions as constant as possible, the pressure re- 
versal points do not check at all closely, and concentration values ob- 
tained at the reversal point by stopping a check run can give but 
approximate values for this reversal point. 
