A paper presented at the Eighty-Fourth General

Meeting held at N e w York, October 14,

1943, H. Yerrnain Creighton presiding.

THE ELECTRIC CHARACTERISTICS OF THE OZONATOR DISCHARGE:]:

By T. C. MANLEY%

ABSTRACT

Oscillographic studies of the ozonator discharge, together with power

measurements, have shown that: (1) The ozonator discharge is inter-
mittent; during each cycle of the alternating voltage there are two dis-
charge periods alternating with two dark periods. (2) During the
discharge periods, the potential drop across the air space has constant
value of -~-eo or --eo depending on the direction of the current. The
quenching of the discharge coincides with the maximum of the voltage
wave. (3) During the succeeding dark period there appears to be no
transport of charges across the air spaces, so that the charges accumu-
lated on the inner surfaces of the dielectrics during one discharge
period remain to influence the starting of the next discharge period.
(4) An equation has been found which gives the power consumption of
an ozonator in terms of the peak voltage, the capacity of the dielectrics,
the frequency and the discharge potential, eo. (5) iVfethods have been
found for measuring Co, which proves to be proportional to the spacing,
d, and the air density: eo/d -- 28.6 kv./cm, at 0~ 760 ram. This is
considerably lower than the potential for spark breakdown at compara-
ble spacing.

INTRODUCTION

The electric discharge occurring in an ozonator differs from other

common types of gaseous discharge in that: first, the path of the
electric discharge through the gas is terminated at one or both ends by
an insulating layer such as glass; and, secondly, alternating current must
be used. 8 Although there are a number of published studies of the
ozonator discharge, mainly in the older literature, 1, ~, 8 these give a far
from adequate picture of the process. The present paper is a study of
the electric characteristics of the ozonator discharge.
EXPERIMENTAL

Both plate-type (Fig. 1) and tubular (Fig. 2) ozonator units were

used. The plate-type units were made of window glass, with glass
spacers, all held together with a suitable cement. Graphite electrodes
# Research Staff, Ozone Processes, Inc., Philadelphia, Pa.
:~ Manuscript received July 14, 1943.
1 W a r b u r g and Leith~iuser, Ann. P h y s i k 28, 1-16 (1909).
Warburg, Z. Tech. Physik 4, 450-460 (1923).
3Klemene, Hintenberger and H6fer, Z. Elektrochem. 4$, 708 (1937).
83

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 84 T.C. MANLEY

were painted on the outside. It will be noted that in this type the
discharge is from glass to glass. Arrangements for maintaining a cur-
rent of air through the discharge space to remove the ozone, and for
passing a different and much larger current of air over the outside to
remove the heat, are not shown. The whole was kept in a steel tank
maintained at the desired pressure. Thermocouples were provided to
measure the temperature of the air entering and leaving the plate, of the
entering and leaving cooling air, etc.

Fig. I. Air cooled plate ozonator (glass-to-glass discharge).

Overall dimensions, 58.5 x 86 cm. Electrode area, 2000 cm. ~
Total glass thickness, 0.30 to 0.32 cm. Air spacing, 0.184
to 0.370 cm.

The tubular unit is shown in Fig. 2, which is self-explanatory. In

this type the discharge is from metal to glass.
Fig. 3 shows the electrical arrangements*: The voltage applied to
* Some o f the methods used were originally developed4, ~, a in studies of the corona dis-
charge from wires, a somewhat similar problem which has been studied very thoroughly
becal~se of its importance in electric power transmission.
9 Peek, "Dielectric Phenomena in High Voltage Engineering," McGraw-Hill Book Co., New
York (1929).
Ryan, =trans. Am. Inst. Elec. Eugrs. (1914).
a r y a n and Henline, Trans. Am. Inst. Elec. Engrs. 43, 1118 (1924).

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 C H A R A C T E R I S T I C S OF T H E O Z O N A T O R D I S C H A R G E 85

Fig. 2. W a t e r cooIed tubular ozonator (glass-t0-metal

discharge). Inside diameter of steel tube, 7.92 cm.;
a i r spacing, 0.215 cm." glass thickness, 0.27 cm.; elec-
trode area, 1,750 era. t Overall length, about 86 cm.

ELECTROSTATIG
VOLTMs
9

TRANSFORMER

~- =

OSCILLOGRAPH OSCILLOGRAPH
CONNECTION CONNECTION
fOR CURRENT FOR POTENTIAL
Fig. 3. ~lectrlcaI connections, (To obtain the charge wave the 50 ohm resistor
is replaced by an 8 microfarad condenser.)

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 86 T.C. MANLEY

the ozonator unit could be varied continuously from zero to 20 kv.

Measurements included the primary voltage, current, power, and the
secondary voltage. The power consumption of the ozonator unit was
obtained by subtracting the transformer and instrument losses from the
wattmeter reading. A cathode-ray oscillograph was used, frequently in
combination with electronic switch, which made it possible to show two
curves (current and voltage, for instance) on the screen at once. A peak
voltmeter was constructed by which the secondary peak voltage, the
maximum exterior charge on the unit, etc., could be measured more
conveniently than by the procedure of scaling the oscillograph pattern.
At low voltages the ozonator functions as a mere condenser, dis-
sipating no power; the oscillogram shows a sinusoidal current wave
leading the voltage by 90 ~ On increasing the voltage, a point is
reached where a small hump appears in the current wave, just ahead
of the maximum of the voltage wave (meters will show a small power
input at this point). With further increase in the applied voltage, this
hump rapidly grows wider and higher, and becomes the dominating
feature of the oscillogram. Fig. 4 shows a typical oscillogram. Curve
e2 represents the potential difference across the terminals of the ozonator
unit; i2 is the current through it.
Study of this and other oscillograms shows that the ozonator dis-
charge is intermittent. During each cycle of the alternating current
there are two discharge periods alternating with two dark periods. The
discharge periods correspond to the two high peaks in the current wave.
The ending of the discharge coincides with the maximum of the applied
voltage, but the time of its beginning will depend on the interior surface
charges accumulated during previous discharges; thus the start of the
discharge quite commonly comes before the zero of the voltage wave.
The dissipation of power in the ozonator is practically limited to the
discharge period, as may be seen from the volt-ampere curve (Fig. 5).
The same conclusion was reached by Klemenc, Hintenberger and
I-I6fer, s who observed the light from the ozonator discharge in a rotat-
ing mirror.
This shows why early attempts by ourselves and others z,8 to treat
the air space as an ohmic resistance led to no useful result. The "re-
sistance" varies from approximately infinity to approximately zero, and
back again, twice in every cycle. The oscillograms often show a number
of small ripples (Fig. 6). It was found that these have nothing to do
with any process of the gas discharge itself, since they occur in the dark
part of the cycle. They are, in fact, a damped oscillation excited by the
preceding discharge peak and the frequency of the ripples is determined
by the equivalent inductance, L, of the transformer and the capacity, C,
of the unit as a whole.*
* T h e r e h a v e been v a r i o u s s t a t e m e n t s 2, 3 in the l i t e r a t u r e to t h e effect t h a t t h e ozonator
d i s c h a r g e is a " h i g h f r e q u e n c y " phenomenon. O f course, t h e F o u r i e r e x p a n s i o n of an i r r e g u l a r
w a v e f o r m such as F i g . 4 or F i g . 6 would go to the l l t h h a r m o n i c a t least, but this is not o u r
i d e a of " h i g h f r e q u e n c y . " O s c i l l o g r a m s s h o w n by K l e m e n c , H i n t e n b e r g e r a n d H S f e r a show
a f a i n t " v e i l " a b o v e the c u r r e n t m a x i m a ; a c c o r d i n g to t h e m t h i s c o n s i s t s of l a r g e n u m b e r s of
v e r y s h o r t peaks w h i c h t h e y a t t r i b u t e to " v e r y short, p o w e r f u l c u r r e n t impulses, following
one a n o t h e r i r r e g u l a r l y , in l a r g e n u m b e r s . " W e h a v e o b s e r v e d t h i s sort of t h i n g only w h e n
t h e a i r in the ozonator w a s wet, or w h e n w e h a d a loose connection in t h e circuit, and even
then not to n e a r l y so m a r k e d a degree. O r d i n a r i l y o u r o s c i l l o g r a m s were perfectly smooth.
T Ewell, A m . J. Sci. I V , 22, 368-378 (1906).
B L u n t , Phil. M a g . V l , 49, 1238-49 (1925).

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 CHARACTERISTICS OF TIIE OZONATOR DISCHARGE 87

Fig. 4. Typical oscillogram of current a n d voltage. Direction

of sweep, left to right. M a x i m u m voltage (smooth curve) about
26.3 l~v.; m a x i m u m c u r r e n t (peaked curve) about 46.5 milli-
amperes.

Fig. 5. Curves computed from the oseillogram (Fig. 4).

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 88 T.C. MANLEY

It was found that during the entire part of the cycle in which luminous
discharge exists ("discharge period") the potential drop across the air
is constant within experimental error. Nevertheless, the current (also
its first derivative) varied by several hundred per cent in this interval.
This would lead to the conclusion that so long as the necessary potential
difference is present (Co) the current through the air depends only on
the associated circuit.t

Fig. 6. Oscillogram showing ripples. Applied frequency, 60/sec.;

frequency of ripples, about 510/sec. L = 15 henries, C = 6.4
~= 10j farad.

This is most clearly shown by comlecting the oscillograph so that the

X-axis displacement is proportional to the voltage, and the Y-axis dis-
placement is proportional to the charge. Fig. 7 shows a typical cy-
clogram obtained in this way. If the arbitrary scale divisions are cali-
brated (by measuring the peaks of voltage and charge with the peak
voltmeter or otherwise), then, if we wish to find the potential difference
? T h e original oscillograms give e~ and i~ Vs. time, all in arbitrary scale divisions. By
noting the interval between corresponding maxima on the oscillogram, the number of scale
divisions corresponding to ~ cycle (180 degrees) is found. U s i n g this, the scale divisions
along the X-axis can be converted into degrees.
The coordinates X and Y are read off (in scale divisions) for as many points as needed,
the X readings are converted into degrees; the curves are replotted, Y against degrees, and
points read off at 10 degree intervals.
By squaring and summing the Y values for the voltage curve, the root mean square
(r.m.s.) voltage is found in scale divisions.
Since the actual r.m.s, voltage has been measured by the electrostatic voltmeter, the con-
version factor needed to change scale divisions (on the voltage c u r v e ) into kv. can be found.
The conversion factor for current must next be found:
By multiplying the corresponding current and voltage values (in scMe div.) at the same
phase angle, a curve of e x i is obtained. A v e r a g i n g gives the ower in (scale div.) ~, and
comparison with the measured power input gives the conversion i~etor for current.
Numerical integration of the current c u r v e gives the c u r v e of charge (q) vs. angle. A n
integration constant must be applied such that the curve (over 360 ~ will be symmetrical with
respect to the X-axis. The potential drop a~ross the glass is q/Cr~ where C~ is the capacity
of the glass alone, calculable from the dimensions. Subtracting the instantaneous values of
q/C~ from the corresponding values of e2 we get ca, the potential drop across the air space
alone.

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 CHARACTERISTICS OF T H E OZONATOR DISCHARGE 89

across the air, we subtract the quantity q/Cg (line FG, Fig. 8a) from
the voltage, which gives the quadrangle A'B'D'E' of Fig. 8b.
Since the "discharge periods" correspond to B'D' and E'A', it is
evident that the potential drop across the air is constant during these

Fig. 7. The q - e loop. Y-axis displacement

proportional to charge, X-axis to potential.

F"
/ ID

/I/
/ l -q (

/e
A ~ ] //
c~) c6)
Fig. 8. Geometrical properties of the charge-voltage loop (schematic).

intervals, at a value of -~-eo or --eo, depending on the direction of the

current. The sharpness of the corner at D shows that the discharge
stops abruptly at the maximum of the voltage.
The slope BD gives Cg, the capacity of glass alone, while the slope of
AB gives the capacity of C of the glass-air combination.

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 90 T.C. MANLEY

1 1 1

C Ca C~
where C. -- capacity of air space.
The fact that the observed value of C checks with the calculated
value shows that there is practically no transfer of charges across the air
space during the dark period.
The power dissipated per cycle is given by the area of the paral-
lelogram A B E D ; it may readily be shown geometrically that this is
C,
4C~eo(em - - --eo)
C
Hence the power dissipated per second is
c.
W = 4fCgeo(em - - - - C o ) (1)
C
in watts (f = frequency)*
This equation (1) has proved to be extremely useful.
The maximum exterior charge qm (point D of Fig. 8b) is obviously
qm : Cg(em -- eo) (2)
Effect of Varying Voltage. Increase in voltage causes the oscil-
lograph pattern (Fig. 7) to become longer, but not thicker. This is
what would be expected--the thickness is 2eo, but the height is qm,
which varies according to Eq. (2).
W h e n the voltage was varied, it was found that the power varied
linearly with the peak voltage, in accordance with Eq. (1). Fig. 9 is a
typical run. It is important to note first, that when e , is less than
eoCa/C there will be no discharge; and, second, the power consumption
depends on the peak voltage, not on the r.m.s, voltage.
Fig. 10 shows the variation of qm, the maximum external charge, as
a function of em. l_Ypto em : eoCa/C, the unit acts as a simple condenser,
(qm = emC) ; after that it follows Eq. (2).
Measurements such as those illustrated in Fig. 9 and 10 provide a
second test of the validity of the theory as well as a much more accurate
method of determining eo, the potential drop across the air.
This eo proved to be directly proportional to the spacing d (Fig. 1 and
2) and the air density 8. This latter depends on the pressure, which was
known, and the temperature in the corona space, which was not very
high, and could be estimated with sufficient accuracy from the tempera-
ture of the cooling medium, heat transfer coefficients, and power input.
Naturally, the temperature is higher at larger values of power, W, but
the deviations thus introduced may be corrected by plotting W / 8 2 vs.
era~8. In any case, the extrapolation to W = . 0 gives the value of eo at
t This equation bears a certain resemblance to equations developed for corona f r o m wires by
Peek, 4 R y a n and I-I'enline, a and by I-Iolm.9 The differences arise from the fact that in the
discharge f r o m wires there is no dielectric, and the volume of the discharge space changes
with the voltage.
g H o l m , Wiss. Ver~ffentl. Siemens-Konzern 4, 14 (1925).

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 C H A R A C T E R I S T I C S O F T H E OZONATOR D I S C H A R G E 91

N~
r~
O9 OS 0~, Or 0,3" OI 0
71YN M.-~./ X...= W ~ W I X IV/,/

taC:h

.~r
bO*~

O.t., o~

0~"/ 00/ o~' 09 o~. o~ o

S'.L .4. V A'I N~ b'~:'lO o"

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 92 T . C . MANLEY

the t e m p e r a t u r e of the cooling m e d i u m . T h e results for eo are g i v e n i n

T a b l e I.

TABLE I
Discharye Potential in the Ozonator Discharge
Pressure, 1.1 to 2.0 arm.; temperature of air in corona space, 5 to 55~ ~
density of air based on $ ~ 1.000 at 0~ 760 ram. ; d ~---air space, in cm.
T y p e of e_Lo
Unit Method* d 8 Bd eo ~d
Plate C 0.184 cm. 1.01 0.185 5.2 kv. 28.0 kv./cm.
-4 0,184 1.01 0.185 5.35 28.9
C 0.184 1.43 0.263 7.75 29.4
A 0.184 1.43 0.263 7.35 27.9
C 0.184 1.86 0.342 9.65 28.2
A 0.184 1.86 0.342 9.85 28.8
A 0.249 1.41 0.352 10.6 30.2
B 0.249 1.41 0.352 10.15 28.9
C 0.249 1.85 0.460 13.55 29.5
A 0.249 1.85 0.460 13.2 28.8
B 0.249 1.85 0.460 12.9 28.1
A 0.260 1.31 0.341 10.0 29.3
A 0.260 1.43 0.372 10.65 28.7
A 0.247 1.31 0.358 9.6 26.8
B 0.307 1.42 0.435 12.8 29.4
A 0.307 1.42 0.435 12.5 28.7
C 0.307 1.42 0.435 12.8 29.4
A 0.307 1.43 0.438 12.6 28.8
B 0.307 1.43 0.438 12.45 28.5
D 0.310 .94 0.282 8.3 28.5
D 0.310 1.01 0.312 8.15 26.2
D 0.310 1.35 0.417 11.9 28.5
D 0.310 1.38 0.428 11.7 27.3
A 0.370 .99 0.365 10.6 29.0
A 0.370 1.42 0.523 14.65 28.0
B 0.370 1.42 0.523 14.80 28.3
Tube A 0.212 1.43 0.303 9.25 30.5
B 0.212 1.43 0.303 8.50 28.1
A 0.215 1.51 0.325 9.55 29.4
B 0.215 1,51 0.325 9.35 28.8
A 0.215 1.315 0.283 7.85 27.8
A 0:215 1.46 0.314 8.85 28.3
A 0.215 1.55 0.333 9.4 28.3
Average 28.6
* Methods: A, power-voltage curve; B, charge-voltage curve; C, from minimum starting
voltage; D, from oscillograms.

DISCUSSION

T h e discharge potential eo p r o v e s to be p r o p o r t i o n a l to the air spac-

ing, d, a n d density, 8, w i t h i n the r a n g e s t u d i e d ; t h e a v e r a g e v a l u e of
eo/3d is 28.6 k v . / c m , with an a v e r a g e d e v i a t i o n of 0.6. T h e result is
c e r t a i n l y accurate within 5 % .
F i g . 11 gives a c o m p a r i s o n of these data with the spark b r e a k d o w n
p o t e n t i a l s , quoted from s t a n d a r d sources, 1~ for parallel plates. I t is
lo Cobine, "Gaseous Conductors," p. 173, Me'raw-Hill (1941) ; Penning, Nederland.
T i j d s e h r . N a t u u r k u n d e 5, 150 (1938).

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 CHARACTERISTICS OF THE OZONATOR DISCHARGE 93

clear that the ozonator discharge occurs at a lower potential. The

path of the discharge current through the air is terminated at one or
both ends by a glass surface (or other insulator) rather than by a
metal electrode. ( W e have found that it makes no difference whether
two layers of glass are used, or only one, so far as the value of eo is
concerned.)
,z
//
/
,P /
}r '~

// /

~t atS O.Z #..~" r ~$" ~@ O,B [.o

4;d er~.
F i g . l l . O z o n a t o r d i s c h a r g e a n d s p a r k d i s c h a r g e (parallel plates). L o g ~d vs. l o g e.

Such a glass surface will naturally be covered with the ions reaching
it in the discharge, or by those left over from previous discharges.
Doubtless this has a marked influence on the discharge mechanism.
LIST OF SYMBOLS USED

Ca Capacity of the air space alone.

Cg Capacity of the glass alone.
C Overall capacity ( 1 / C --" 1~Ca + 1/Cg).
d Air space, cm.
e Instantaneous value of voltage (in general).
e2 Instantaneous value of secondary voltage.
ea Instantaneous value of potential across air space ( ~ Co during
discharge period).
em Maximum value of secondary voltage.
Co Discharge potential across air space, kv./cm.
f Frequency.
i Instantaneous value of current (in general).
i2 Instantaneous value of secondary current.
L Equivalent inductance of the transformer.
q Charge.
qm Maximum external charge.
W Power, watts.
8 Density of air relative to 760 ram., 0~

Resumen clel a r t ~ c u l o : " L a s C a r a c t e r ~ s t i c a s , E l ~ c t r i c a s d e la D e s c a r g a

en un Ozonizador"
La descarga el6ctrica en un aparato para la producci6n de ozono
difiere de otros tipos comunes de descarga en que uno o ambos t6rminos
de la descarga tienen lugar en una superficie aislante de vidrio, y e n que
se ha de emplear corriente alterna.

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 94 T.C. MANLEu

S e u t i l i z a n dos t i p o s c o m e r c i a l e s d e o z o n i z a d o r , el u n o f o r m a d o d e d o s
l f i m i n a s de v i d r i o ( F i g . 1 ) , y el o t r o ( F i g . 2 ) d e u n t u b o de v i d r i o y u n o
d e a c e r o . Si se a p l i c a u n v o l t a i c r e d u c i d o el a p a r a t o , c o m o u n c o n d e n s a -
d o r , n o tlene p f i r d i d a s elfictricas. P e r o al a u m e n t a r el v o l t a i c a p a r e c e e n
las o s c i l d g r a m a s u n a c o r c o v a en la o n d a d e c o r r i e n t e ( q u e c o r r e s p o n d e
a u n a d e s c a r g a e l f i c t r i c a ) , la c u a l se e n s a n c h a y e n a l t e c e , i n d i e a n d o
p 6 r d i d a de e n e r g i a . C u r i o s a m e n t e , la d e s c a r g a p u e d e c o m e n z a r a n t e s d e
l l e g a r el v o l t a i c a cero, d e b i d o a c a r g a s r e s i d u a s del m e d i o ciclo a n t e r i o r .
D u r a n t e la d e s c a r g a el v o l t a i c se m a n t i e n e c o n s t a n t e p e r o la e o r r i e n t e
v a r i a . E s t a d e p e n d e p o r lo t a n t o del r e s t o del c i r e u i t o elfictrico. S e
d e r i v 6 u n a e c u a c i d n p a r a el g a s t o en r a t i o s ( e c n . 1 ) , q u e se h a m o s -
t r a d o m u y fitil.

DISCUSSION
W. W. WINSI~IPll: In what kind of glass were these experiments made?
T. C. MANLEY: The tubular ozonator was made of pyrex glass tubing.
W. W. WINSHIP: Have you any reason to think there would be significant
differences in the behavior with various kinds of glasses?
T. C. MANLEY: As far as I know, the important thing about different glasses
is the difference in dielectric constant. These results were obtained with two dif-
ferent types of glass and two different types of equipment and the results corre-
spond perfectly with each other. If there were any effects due to surface dif-
ferences, such have not been observed.
W. W. WlNS~ItP: There might be a difference in behavior if it was tested with
a wide range of glasses.
T. C. MANLEY: It is possible.
COLIN G. FINE12: Would there be any advantage in using quartz instead of
glass ?
W. C. MANLEY: There are certain advantages in using quartz. It has a very
low dielectric loss and it is resistant to temperature. However, for efficient ozone
generation ozonators must always be so operated that the temperature is kept
down. Outside of that I would say you would simply consider quartz as another
type of glass.
COLIN G. FINK: Looking at your curves, is there any effect due to traces of
nitrous oxide? I assume there was no nitric oxide in your ozone, but just in case
a trace got in, how would it affect the conductivity--would it not increase the
conductivity ?
W. C. MANLEY: I do not know that it would have very much of an effect. We
have found the amount of oxides of nitrogen to be less than 1% of the amount
of ozone formed. Of course, the air going through contains a certain amount of
ozone because of its formation and therefore must have contained still smaller
amounts of oxide of nitrogen. W e have not found that the concentration of ozone,
therefore of oxides of nitrogen, had any great effect upon the curves. Another
thing might be mentioned water vapor, which has a very marked influence on
the amount of ozone formed, seems to have practically no influence on the elec-
trical properties.
GEO. GLOCKLER~a: How can one think of the discharge of an ozonator? Is it
like a point discharge, when millions of point discharges are happening at any
given time ?
11 M a n a g e r , T h e r m a l S v n d i c a t e Ltd,, N e w Y o r k City.
1~ H e a d . D i v i s i o n of E l e c t r o c h e m i s t r y , " C o l u m b i a U n i v e r s i t y , N e w Y o r k City.
13 H e a d , Dept. of Chem. & C h e m . E n g . , S t a t e U n i v e r s i t y of I o w a , I o w a City, I o w a .

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 CHARACTERISTICS OF THE OZONATOR DISCHARGE 95

T. C. MANLEY: T h a t is a very hard question to answer. V e r y frequently the

discharge appears to be perfectly uniform, but not always. The apparatus I showed
you was so arranged that you could not see the discharge, so I cannot say w h a t
it looked like. W e had other equipment in which we could see it, and one t h i n g
very noticeable is that the appearance changes strikingly with the amount of
moisture in the air.
F. A. LID~URY14: W h a t explanation have you for the little "hobs" on the cur-
rent curves, which you might call harmonics? Are they harmonics?
T. C. MANLEV: Yes, but those little ripples are not of much importance. They
are determined by characteristics of the main circuit.
J. S. SMATK01~: Several months ago the A. C. S. News Edition 1~ c a r r i e d a
heated discussion pertaining to nitrous oxides. I was wondering if, perhaps, the
nature of the voltage curve had any effect upon the production of nitrous oxides
in relation to the ozone composition. The discussion in the News Edition would
seem to indicate that the dielectric had something to do with it because the dis-
cuss~on occurred between two companies manufacturing plastics being used as
dielectrics ; apparently, to them, the dielectric was the answer to any query on the
peak voltage effect.
T. C. MA~CLEY: W e have not studied the production of oxides of nitrogen espe-
cially as a function of the operating voltage. Under normal conditions of opera-
tion a fairly high peak voltage is used; we found that the amount of oxides of
nitrogen produced was extremely small. In the article in the News Edition,
reference was made to some conditions under which the oxides of nitrogen m i g h t
reach 70% of the ozone concentration; I am sure those must be very exceptional
conditions because we have never been able to observe them.
VICTOR HA~N~7: I would like to add a few remarks to what Dr. Manley said
about oxides of nitrogen. F o r one thing, I think the two experimenters w e r e not
reporting under exactly comparable conditions. C. E. Thorp, who s t a r t e d the
controversy, was interested in very low concentrations of ozone--a few parts per
million. U n d e r those conditions it is quite possible that the percentage of oxides
of nitrogen relative to the percentage of ozone is much higher than with w h a t we
consider standard conditions, which are concentrations of 1% or higher, in the
ordinary ozonator. W e have done considerable work measuring both oxides of
nitrogen and ozone, and have found that the amount of ozone is usually 90 or
100 times the amount of oxides of nitrogen. W e have seldom run into a case
where the percentage of oxides of nitrogen based on the amount of ozone is m o r e
than 1%. W e have studied several types of dielectrics and found no difference.
In other words, we studied dielectrics of several types of glass and plastics and
there was no significant difference shown for oxides of nitrogen for one type of
dielectric over another.
V. S. DE MARCI-IllS: Can you observe any effects when you have moisture or
when you have dust particles going through the ozonators?
T. C. MANLEY: The moisture situation was shown by one experiment in w h i c h
we accidentally had very moist air going through. The electrical characteristics
were not changed by that. Regarding the dust--you must bear in mind that the
air has first to go through a drying system and various meters, etc., before reach-
ing the ozonator, so that I feel the dust situation is probably standardized. N o
visible dust deposits were found on taking the apparatus apart. Of course, you
could easily imagine rather extreme cases where you might have so much dust
that if built up a thick deposit on the electrodes. This would decrease the spac-
ing and a layer of dust would act as an additional layer of dielectric. Such a
condition might well change the characteristics. Practically, it would soon result
in plugging the air passages up altogether and you would have to take the equip-
ment apart and repair it.
14 Oldbury Electro-Chemlcal Company, Niagara Falls, N. Y.
1~Graduate Student, Dept. of Chem. Fng.. Columbia University, New York City.
taInd. Eng. Chem. 19, 686, 1102, 1473 (1942).
17Director of Research. Ozone ProcesSes Inc., Philadelphia, Pa.
18Institute of Gas Technology, Chicago, Ill.

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 96 DISCUSSION

REVIEWER: This is an excellent report upon an investigation which is an im-

portant contribution to our knowledge of the phenomena occurring in a brush
discharge ozonator.
I wish Mr. Manley would supplement this work by employing high frequencies.
There are several important fields for ozone which are awaiting less expensive
ozone production. In my opinion the most promising improvement is the use of
frequencies of the order of 10,000 cycles.
I have found that the yield of ozone from an ozonator is very closely propor-
tional to the current. W h e n the temperature rises, both the current and the pro-
duction of ozone increase. Von Ladenberg found that at moderate frequencies the
increase in ozone production was relatively small. A t high frequencies such as
employed by Siemens & Halske (10,000 cycles), upon my last visit to Siemenstadt
in 1939, both the temperature and the yield per kw-hr, were greatly incre~tsed,
the temperature becoming so high that insulated water-cooling of electrodes be-
came necessary. A t these high frequencies the characteristics might be quite
different from those reported in this paper.
I am particularly interested in the " d a r k periods" which the author has dis-
covered when there is no discharge. W e do not know how much of the ozone
from an ozonator is contributed by the re-formation into ozone of the oxygen ions
c a r r y i n g the current, and how much is produced by ultraviolet radiation below
2,000 X particularly at 1,850 ~. It would be very interesting if it would be pos-
sible to measure the radiation with a platinum photocell and compare it with the
ozone produced. ( T h e ozone concentration is, of course, dependent upon both
the ozone produced and the amount decomposed. 10)
T. C. MANLEY (Communicated) : I agree that work at high frequencies would
be very interesting; perhaps when it again becomes possible to obtain electrical
equipment, we may do something of the kind.
Probably the best work on high frequency characteristics was that done by
S t a r k e 3 ~ His results show that the power input at constant voltage is propor-
tional to the frequency; the ozone production of a given tube is also proportional
to the frequency, provided the flow of air or oxygen is adjusted to give the same
concentration. U n d e r these conditions he found that the e~ciency ( g . / k w - h r . )
was independent of the frequency.
H i g h temperature in the corona space must be regarded as a distinctly unde-
sirable by-product of high frequency operations; we have found that a 40 ~ C rise
in the corona temperature reduces the efficiency by 25% to 50% (depending on
other conditions).
While nothing final can be offered regarding the mechanism of formation of
ozone, I do not think it involves ionized oxygen ;. even a rough calculation shows
that the number of ozone molecules formed exceeds the number of oxygen ions
formed in a ratio of 10,000:I, or greater.
In the matter of current and current yield, the charge t r a n s f e r r e d across the air
C,
space in one half-cycle is Cg(em - - - - e o ) , hence the average current (not the
C
C,
r.m.s.) is 4fC,(e,, - - eo), or W/eo, which should be used for calculating
C
current densities, current yields, etc. ; it is the writer's opinion that power efficiency
( g . / k w - h r . ) is of more significance than current efficiency, which apparently is
proportional to eo, i.e., to the spacing and air density.
xgA. W. Ewell, J. Applied Phys. 13, 759-767 (1943).
m Z. Elektrochem. 29, 358-364 (1923).

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