239
V O L U M E 2 6 , N O . 1, J A N U A R Y 1 9 5 4 Satisfactory checks wiLh the theoretical values were obtained for esters of various unsaturated acids using the hydrogen as received, without further purification. .4purification train for the removal of oxygen is described by Prater and Haagen-Smit (6). CATALYSIS
A 0.1-gram quantity of platinic oxide was used successfully with various acrylic, maleic, and fumaric esters. The reaction was usually 99% complete, or more, in 1 hour of agitation, 3 hours being allowed for the determination. For the hydrogenation of maleic anhydride and viscous polyesters a satisfactory rate of reaction was obtained with a more dispersed catalyst, 10% palladium on activated charcoal powder. Both catalysts were made by Baker & Co., Inc. HJ drogenations which are somewhat too slow for practical analytical purposes may be accelerated by heating the reaction flask slightly. A convenient means of applying heat is to wind electrical heating tape around the reaction flask. -4successful
reaction was carried out in this manner a t 80’ C. The flask was cooled to room temperature for volume readings. ACKNOWLEDGMENT
The advice and suggestions of Karl Klager and F. R. Hepner of the Aerojet laboratories are gratefully acknowledged. LITERATURE CITED
(1) Gatterman, L., and Wieland, H., “Laboratory Methods of Organic Chemistry,” p. 376, London, Macmillan Co., 1943. (2) Hyde, J. F., and Soherp, H. W., J . Am. Chem. SOC.,52, 3359 (1930). EKG.CHEM.,ANAL.ED.,13, (3) Johns,I. B., and Seiferle, E. J., IND. 841 (1941). (4) Noller, C. R., and Barusch, 31. R., Ibid., 14, 907 (1942). (5) Prater, A. N., and Haagen-Smit, A. S., Ibid., 12, 705 (1940). (6) Savacool, R. V., and Ullyot, G. E., ANAL.CHEM.,24, 714 (1952). (7) Vandenheuvel, F. A , , Ibid., 24, 847 (1952). (8) Zaugg, H. E., and Lauer, W. AI., Ibid., 20, 1022 (1948). RECEIVED for review M a y 1 5 , 19.53. Accepted September 4, 1953.
Mechanism of High-Frequency Titration SHIZUO FUJIWARA and SHalCHl HAYASHI University of Electro-Communications, 1-5 Shimomeguro, Meguroku, Tokyo, Japan
T H I S papei is a contribution to the study of the theoretical aspects of high-frequency titration. Results have been obtained with apparatus capable of giving the necessary data, to explain the response of a high-frequency analysis apparatus, where the solution vessel is placed in the coil of the tank circuit. In addition to the regions of sensitivity recently given by others, the apparatus and method described reveal an additional region of sensitivity in the range 0.1 to 1.0s (for hydrochloric acid) not previously reported. The apparatus is unique in that it uses a modulated resonance frequency source and an “infinite-impedance” detector followed by an audio-amplifier and a vacuum-tube voltmeter. The solu-
A
tion to be studied is placed in a glass vessel in the coil of a tuned circuit and the voltmeter output is plotted as a function of the dial setting of the resonance frequency source. For each solution so studied there are obtained the frequency of maximum resonance and the magnitude of the output at maximum resonance. The sensitivity characteristics of the instrument are then obtained by plotting the resonance frequency and the maximum output a t resonance as a function of concentration for various electrolytes. Recently several studies ( I , 6, 18) have gone far toward explaining the results of high-frequency titrations on a sound theoretical basis. These studies were all based upon apparatus in which the solutions studied were placed in capacitor-type cells.
B
0
+B Figure 1. c1.
C2.
ci C1n. c,:CS, CI,. c6, cl1. Cn,
c7.
C9, CIS.
460 100
pf. pf.
0.01 pf. 10 pf. 0.1 ut.
6
pf.
0.005 p f .
Schematic Diagram of Apparatus CLOTci6.
ri, r18. rl, r7, rid. rs. r4, r5. re. ra, ri6.
0.05 pf. 100 Kw. 500 Kw. 1 Kw. 250 Kw. 30 Kw. 1 Kw.
r9, rii, riz, ria. rlo, rn. rln.
VI. Vi.
Vs. V.V.
6SN7
6SJ7
50 Kw. 20 Kw. 1 Kw.
6SN7 Tube voltmeter
240
A N A L Y T I C A L CHEMISTRY
The object of this paper is to present the results of an attempt, with apparatus capable of giving the necessary data, to explain the response of a high-frequency analysis apparatus where the solution vessel is placed in the coil of the tank circuit. This study reveals a region of sensitivity in a higher concentration region than any previously reported.
1.5
-z
-'-
x-
YT--
'
'.3
4PPARATUS AND METHOD
In order to analyze the response of high-frequency titration data, a t least two factors must be measured a t the same time. Accordingly, an apparatus has been constructed in order to observe precisely the resonance frequency and a voltage proportional to the resonant voltage of the tank circuit where the solution vessel is placed in the coil. Figure l a shows a block diagram of the complete apparatus and Figure l b s h o w a circuit diagram of the tank circuit, detector, and amplifier. Radio waves of approximately 2.54 or 5.98 Mc. modulated a t 1000 cycles are produced by an Oki No. 102 signal generator. These are fed to the detector circuit ( L z ,Ci. 1/2 6SN7) through the electromagnetic coupling between L, and Lz. Coils L1 and Lf are made of copper tubing 6 mm. in diameter. The coils have, respectively, 6 and 13 turns, and theii diameter is 100 mm. The coils are maintained about 5 em. apart. The &-value of the circuit is maintained very high by the "infinite impedance" detector circuit. After amplification by the 6SJ7 and 6SX7 tubes, the output voltage is measured by a vacuum-tube voltmeter. The solution to be studied is placed in a glass tube 50 mm. in diameter and 250 mm. long, which is placed in coil Lp. The coils, detector circuit, and amplifier are completely shielded. The surface of the solution lies 35 mm. above the shielding box. At 2.54 Mc., when the glass tube is empty, or when it is filled with 250 ml. of distilled water. the &-value of the tuned circuit is 318. The measurement of the &-value of circuit LOand C, containing the solution is carried out as follows. The vessel containing
i, 035'
+
~~
-3
1525(5;f)
io
Figure 3.
I
IO
10'
io1
104
IO*
ioi.
Relation of iMaximum Resonance to Concentration a.
Hydrochloric acid
b. Acetic acid
350 ml of a solution is placed in coil I,?. The tuning condeii>er, C1, is fived to tune L? and C1 to the frequency of the experiment, say 2.54 hIc., and remains fixed throughout the remainder of the experiment. The output voltage is measured by the vacuum-tube voltmeter. The frequency of the signal generator is changed by about 4 kc. (one scale division of the calibrated dial) and the output is measured each time the frequency is changed. The resonance curve is obtained by plotting the signal generator dial reading aa abscissa and the vacuum-tube voltmeter readings as ordinate
1.4-
1.2-
c 3
5 1.0 U
In Figure 2 are plotted curves for several different concentrations of hydrochloric acid. The maximum point of each curve represents the resonance frequency and the magnitude of the maximum resonance for each solution.
~
i f -
EXPERIMENT4L RESULTS
P z 4
0.8
0
M
9
-
:
I 2
.
-
2 0.6
0.4 .
, 0.2
t
I .
,
168
166
110
114
172
116
Figure 2. Resonance Curves of Circuits Containing Solutions of Hydrochloric Acid of Following Concentrations (N) s. 1. 0 (distilled water) -. io-: 6. 2-x 10-1 2. 103.
4.
10-5
10-4
7.
8.
2
x
10-1
10-2
According to Figure 2, the resonance frequency changes only slightly with concentration, but the magnitude of maximum resonance changes rather markedly. In Figure 3 the maximum resonance voltage and the resonance frequency are plotted as a function of the concentration of the solution for hydrochloric acid and for acetic acid. These data are for 5.98 Mc. For the purpose of discussion, these curves may be divided into three regions, X , Y , and 2, separated by one minimum point, Pl, and one maximum point, P2, shown in Figure 3. Similar curves were obtained for hydrochloric acid, sodium chloride, and sodium hydroxide at 2.54 Mc., except that the minimum, P,, is less pronounced (Figure 4). In region X , the resonant maximum increases a8 the concentration of the solution decreases, and finally attains the value of distilled water. In region Y , the resonant maximum increases with increase of concentration to the mas4mum at P2. As the concentration becomes still greater, the value of the resonant maximum decreases rapidly. -1s it
V O L U M E 2 6 , NO. 1, J A N U A R Y 1 9 5 4
241
T [I
Curve c is in the region 1 where the end point is a rnaimu?. sensitivity is good, and since the slope of the curve of Figurp 9 is negative in this region. the resonant value a t the end point is a minimum. Curve d is in sensitivity region 2. This region of rather good scmsitivity for this apparatus occuri in a relatively high concentration of electrolyte. Because of the logarit,htnic concentration plot of Figure 3, this sensitivity is not 50 great as might a t first be thought, but this region of sensitivity has not been mentioned in any previous publications.
1.5
1
10
Figure 4.
lo-' 10 10 3 10 CONCENTRATION
G
I
The authors are indebted to thc Research Fiiiitf o f the ]':ducation M i n i - I r y for financial support. Thanks are also riuc' to professor Kenjiro Kimura at Tokyo University for valuable suggestions.
I
REFERENCE5
Relation of Jlaxiniuin Resoriaiic.e C O I I C ~ ratinn III Exwrinirnt r.#rriwl out
to
c9
2.54 \ l e .
st
ACKNOR LEDGMENT
T
10 ' 10-1
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i ,
.
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.
.
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,
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t
W-. J., ; \ l a l ~ ~ l stadt, N. V., Petitjean, D. L., and Anderson. W. K., ANAL. CIIPX., 24, 1240 (1952). (2) Rlaedel, W. J., et nl.,
(1) Blaedel,
I
~
I
I
lo-.
10
a
10
I
DISTILLED WATER
Ibid., 24, 198 (1952). (3) Fujiwara, S., and Hay-
HCI CONCENTRATION
Figure 5 .
Relatioil of (:oncentratioti Maxim 11m Resnnanre
IC,
Solid line a.
b.
2nd. 4 ml.
d l
;
ashi, s., Report of T7niElectro-Comm u n i c a t i o n s , No. 1 , versity
- . "-;'
-
119 (1950). (4) Thad., 30. 2, 322 (1960). (5) Ibid., No. 3, 91 (1951). I C JC 50 3 C (6) Hall, J., A N a L . CHFM., 24, 1236, 1244 (1952). Figiire 6. Titration I., Report o f Radiation Lahwiltory, 6, 131 (1952). (20) West, P. W., Burkhalter. T. S.,anti Broussard. Leo. k s . ~ ~ . CHEM., 22, 469 l,Injo!. ~
14
-
nlay be assumed that changes i n rf~sonancrfrequent.>. :ire tluiprincipally to changes in inductanw or capacitance of t tic, tuned circuit,, and changes in the value of maximum resoilatice arc' riucx to changes in resistive loading. it may he concluded from the data shown in Figure 3 that rwistive changes are significant a t both higher and lower coticwitriitions t h m are ca.paritivc, or i l l ductive changes. Experiments were carried out i n tvhich 2, 1. :jnd ti nil. of I S sodium chloride were added to thr a a t e r in thr glass vessel befow addition of the hydrochloric avid was begun. Thrw data ai'cx shown in Figure 5 , and indicttiti. the eliminat,ion of the varin.tiollr: in the X and Y branches of the curve, but the vttriation in tlic region Z is ret,ained. -4s regions 9 and Y are t>hemost. sensitive regions for titration, it is not desir:tble to add ions or wits not participating in the reaction. As has been shown previously ( I , 6 , IS), there :ire yrrttt diffwcnces bet,ween the acid-b:w titr:r.tion curves of solutions having different c,oncentrat,ions. Figurc 6 shoFs t,he results of titrations with the apparatus described here at several different concentrations of acid a n d haw. Tn Figurc 6. cun'r a ii; in the part of sensitivity region X where littlr (4Ii:i:ige of rrson:int voltage or frequency should be espec~tctl. Curve h is in the part of region X where the seiisitivity is good. anti since the slope of the curve of Figure 3 is positixro i n this region the resonant value a t
RECEIVEDf o r reyiew- OctohPr 15, 1962.
.lecr),tt,~I
21. I!lJR.
