1590
ANALYTICAL CHEMISTRY
ure simultaneously a number of constituents in a single gas sample. Kitagawa’s method for phosphine and hydrogen sulfide in acetylene is a step in this direction. The problems to be solved in attaining this goal are serious, two of the main ones being to avoid interferences and to develop specific sorbents which will retain the desired constituent and pass others. There are numerous gases and vapors for which there are as yet no suitable portable methods of detection and measurement. There would seem to be some possibility of adapting colorimetric reactions in solutions to similar methods on gels. ACKNOWLEDGMENT
The authors express their gratitude to W. P. Yant, E. \V. Gilliland, and P. W. McConnaughey of the Mine Safety Appliances Co., Pittsburgh, Pa., for their advice and suggestions and for the loan of equipment and materials. They are also indebted to the Mine Safety Appliances Co. for the grant of financial support, through the Purdue Research Foundation. LITERATURE CITED
(1) dnglo-Iranian Oil Co., J . Inst. Petroleum, 2 5 , 356 (1939) (2) Belcher, R., Anal. C h i m . A c t a , 1, 417 (1947). ( 3 ) Belcher, R., J . SOC.Chem. Ind., 64, 111 (1945). (4) Carhart, H. W., and Krynitsky, J. A., U. S. Patent 2,531,229 (1950). ( 5 ) Cole, J. W., Salsbury, J. hl., and Yoe, J. H., Anal. Chtm. A c t a , 2 , 115 (1948). ( 6 ) Davis, P. B., V. S. Patents 2,460,065 to 2,460,074 (1949). ( 7 ) Elkins, H. B., “Chemistry of Industrial Toxicology.” New York, John Wilev & Sons. 1950. (8) Farr, W. H.,”Fagen, TT-. E., and Kolanowski, S.C., C . S. Patent 2,553,179 (1951). (9) Grosskopf, K., Angew. C h e m . , 63, 306 (1951). 110) Hall, G L., Annual report, Bureau of Sanitary Engineering, Maryland State Dept. of Health, 1940 (pub. 1941).
Hubbard, B. R., and Silverman, L., Arch. Ind. H y g . Occupational Med., 2, 49 (1950). Ingram. G., Anal. Chim. Acta, 3, 137 (1949). Jacobs, h l . B., “Analytical Chemistry of Industrial Poisons, Hazards and Solvents,” New York, Interscience Publishers, 1949. .Jacobson. E., Granville, W. C., and Foss, C. E., “Color Harmony Manual,” 3rd ed., Chicago, Container Corp. of America, 1948. Kitagawa, T.. Japan. Patent 176.510 (19481. Ihid., 176,805 (1948). Ihid., 177,024 (1948). Ibid.. 178,082 (1949). Kitagawa, T., private communication. Kitagawa, T., Repts. T o k y o Ind. Research Inst. Lab., 44, 1-19 (1949). Klug, C . IT., U.S.Patent 2,549,974 (1951). Littlefield. J . B., Ibid., 2,174,349 (1939). hlellon. $1. G., Rccord Chem. Progress (Kreage-Hooker Sci. L i b . ) , 11, N o . 4, 177 (1950). Mine Safety Appliances Co., Bull. DS-4. I hid., DY-3. Munch, R. H., Ind. Eng. Chem.. 43, KO.9, 99 .I (1951). Sasaki, R., Bull. Agr. Chem. Soc Japan, 4, 38 (1928). Setterlind. A. N., Am. I n d . Hug. Assoc. Quart.. 9, 35 (1945). U.S. Patent 2,487,077 (1949). Shepherd, G. M., Shepherd, M . . ANAL.CHEM.,19, 77 (1947). Taylor, H. D., Knoche, L., and Granville, IT. C., “Descriptive Color Kames Dictionary,” Chicago, Container Corp. of America, 1950. ‘I‘nited States Safety Service Co., advertising literature. Van Arsdell. P. M., Petroleum Engr.. 21C, No. 6, 26: KO.8,30; KO.9, 16; No. 10, 16: KO.12, 17 (1949); 22C, S o . 1, 17; So. 2 . 19 (1950). Zhdanova. N. V.. Slusareva. R. L., and Tesner. P. .I..Zacodskoya Lnh.. 15, 647 (1949). RECEIVED for review December 7, 1951. Accepted July 18, 1952. Presented before the Dirision of Analytical Chemistry a t the l 2 l s t Meeting of the . ~ E R I C I P CHEMICAL SOCIETY, Buffalo, N. Y. Based in part on material rontained in the doctoral thesis of G. D. Patterson, Jr., Purdue University.
Conductance Instrument for Standardization of Volumetric Reagents RALPH H. M ~ L L E R AND ~ ALFRED M.VOGEL* Washington Square College of drts and Sciences, .\‘ew York University, New York 3, Conductance is a sufficiently sensitive function of concentration to be useful in quantitative analysis. Such conductometric analysis has required either calibration curves or analytic functions together with baths giving good temperature regulation. The aim of this investigation was to devise a conductance instrument that w-ould eliminate the need of temperature regulation and give normalities directly with sufficient precision for analytical
ONDUCTASCE is a sufficiently sensitive function of concentration t o beuseful for analytical purposes ( 3 ) . Calibration curves or analytic functions have been used, but because of the 2% temperature coefficient, good temperature regulation has been required. This has severely limited the use of conductance in analytical chemistry. The purpose of this investigation was to devise an instrument sufficiently precise for analytical purposes that would read normality directly, eliminating the 1 Present address, Los Alnrnos Scientific Laboratories. P.O. Box 1663, Los .&lamos, h’. 31. Present address. Adelplii College, Garden Citj-. S . T.
N. Y.
purposes. An instrument is described that has a linear scale reading directly in units of normality. It is automatically temperature compensated b?means of a thermistor network. Results obtained for two electrolytes in the analytically interesting range 0.09 to 0.11 ,?-and from 18” to 33” C. are given. This instrument offers simple, rapid standardization of volumetric reagents, with good precision, using relative1)- small aniounts of solution.
need for costly temperatule regulation by introducing temperature compensation. This temperature compensation can be accomplished conveniently by placing the conductance cell in one arm of a Wheatstone bridge and placing in the second arm another resistance whose resie tance-temperature relation is closely similar t o that of the solution. For this compensating resistance, a network consisting of a thermistor ( I ) in series mith a fixed resistance is used, both being shunted by a second fixed resistance. The thermistor is immersed in the center of the conductance cell, so that its temperature is alnnvs the same ns that of the solution
V O L U M E 24, NO. 10, O C T O B E R 1 9 5 2
1591
It was necessary to have detailed conductance-concentrationtemperature relations for the analytically interesting 0.09 t o 0.11 .\*range arid from 15" to 35" C. A search of the literature yielded no information applicable to the problem and it' therefore was necessary t o determine the conductance-concentrationtemperature variations for some electrolytes, before proceeding with the instrumental problem. Those used so far are potassium 1-hlorideand potassium dichromate. The normality of the dichromate was based on oxidation-reduction use. The conductance tinta acc.umulated are the subject of another paper heing prepared for publication. In the roncentration range 0.09 t o 0.11- \ I and throughout t'he teniper:iture range 16" to 33" C., the relation betv-een normality BIR, :ind resistance can be expressed by the equation A- = d where d and B are empirical const,ants determined by the least squares method. The values calculated from the above relation :igreed, on the average, with the measured values to better than 0.027, for both electrolytes. For the concentration range of interest the temperature coeffic,iwt \vas virtually constant. IVhile there was some drift with (.onrentration, in the worst case this was 0.03% of the average value. The results of the temperature coefficient measurements (*:inhe expressed by the equations
+
- 1) - Y&(R> - 1 ) + TlTZ(R2 s = 7'o[T1Rr(R1 T?R?(Ri- 1) - TiRi(Rz - 1) + To(R2 - Ri)
T,, T 2 ,and Toare the resistances of the thermistor a t temperatures t y , ti, and t: C., the last a reference temperature. R, and R2 are the ratios of the electrolytic solution resistance a t f y and ti to the resistance of the solution a t the Fame reference temperature. The value of the shunting resistor is given by
.in average value of S \vas calculated. From this value a v t of values of P was found and an average P was then taken. For potassium chloride S was 204.60 ohms and P was 1395.3 ohms. For potassium dichromate S was 215.72 ohms and P vias 1425 5 ohms. A fixed resistor of 200 ohms was used in series with a 0- to 100-ohm ten-turn 0.17, linear potentiometer to form the resistance S. For the shunting resistance P , a 1000-ohm fixed resistor, was used in series with a ten-turn 0- to 500-ohm O.lCc linear potentiometer. For the compensating network the worst match betv-een electiolyte and network was good to 1 part in 1500. Potentiometer setting errors up to half a division would lead to values off by less than 1 part in 4000 and have negligible effect on compensation.
RT = Ra(l + 0.00075266e2415.10/ T)/4.0127
-
for pot~esiumchloride and
RT = Ro( 1 foi,
Kl]
LUDS
POLYETHYLENE HANDLE-
+ 0.00066346e24~~.13,'~)~3.i767
potassium dichromate.
RT is the resistance of the solution at, 1'" A. and Rois tlie reaist:inre of a solution of the same normality at the reference temperatu1.e 201.16" A. On the average t,he values calculated from these c~quationsdiffered from the measured values by lees than 0.0270 tor both electrolytes. These equations were used to calculate wsistance values at intermediate temperatures u-here the compensation network values were being computed. \Yestern Electric thermistor Type 25A was selected for the c~~mpensationnet\+-ork. The characteristics were determined antl c:m he expressed with the desired precision by the equation Log
(2 +
0.02)
=
-5.55526
+ 1654.795iT'
whwe RT is the thermistor resistance at T o A. and ROthe resist:tni*r at 297.41" A , , a reference temperature. For the partivular thc~riiiistoi~ used Ro\\-as336.10 ohms. APPARATUS
Normality Scale. I n a Wheatstone biidge R = RIRz/R1, \\here RS is the resistance of the arm opposite the unknown. Ka and ( - A S )have the same inverse relation to R, the soluS ) / B . .4 fixed resistance tion resistance, making R3 = A ( - A antl a linear potentiometer representing - A and S,respectively, torm R3 The potentiometer was calibrated with a linear normality vale, the same scale for both electrolytes. For each electrolyte, the value of the fived resistance depends on the difference in the ie\istance between the 0.09 and 0.11 S settings. For the particular potentiometer used the difference between Rs a t 0.09 and 0 11 is 68.29 ohms. This gives 12 = 68.29B/0.02. This value of k together with the values of A for each electrolyte gave 326.8 and 322.0 ohms as the magnitudes of the fixed resistances for potassium chloride and potassium dichromate, respectively. The actual components used were two linear Beckman Helipots in series. The first was a ten-turn 0- to 500-0hm0.17~potentiometer to give the fixed resistance settings. The second was a three-turn 0- to 100-ohm 0.5% potentiometer for the normality scale. Two ten-turn Beckman Duodials were used for resistance settings, t h a t for the normality scale positioned so as to read normality directly. A 0.5c7, linearity would not assure a scale precision of better than 1 part in 1000. Thepotentiometer used, however, showed a linearity of bettei than 0 17% all over the scale. Temperature Compensation. Either arm R1 or Rz may be used for temperature compenration. The value of the sprier: resistance, ,5', is
+
A\-
+
POLYETHYLENE
CELL SPACE n
-
II
U
,.
CELL CUP tI
Figure 1.
1.-
Cell
r.
rib
IHi
The last bridge arm consisted of Y set of four General Radio Co. decade resistors giving values from 0.1 to 1111.1 ohms. This arm accommodated the other variables-cell constant, specific conductivity of each electrolyte, and constant B from the normalitv scale. Empirical settings were used. The resistances and potentiometers used in the bridge were made of manganin wherever possible to minimize the effect of room temperature. For the normality scale potentiometer where nianganin was not used, a change of 10' C. in room temperature affected the calibration of the scale by less than 0.0470,since it was in series with a much larger manganin resistance. Because of the asymmetry of the bridge, a Wagner ground coniposed of two equal 1000-ohm resistors in series \\-ith a 1000-ohm potentiometer was built into the bridge. Small capacitors in the range of 75 to 300pfif. were used in parallel with the Beckman potentiometers to offset some quadrature differences, seemingly due to the inductance of these potentiometers. The Cell. The cell was made of polyethylene. I t was in the form of a dip cell, with internal dimensions of approximately 1 x 3 x 1.5 cm. and fitting into a cup, giving what was as close as possible to a machined fit. The platinized platinum electrodes were sealed into the 1 X 1.5 cm. ends and were slightly smaller in their dimensions. The thermistor, insulated by a thin film of Tygon rack coating compound made by the U. S. Stoneware Co., was sealed into the roof of the cell. The glue used was polyethylene dissolved in toluene. Figure 1 gives the details of the construction. The cell was conveniently plugged into and removed from the bridge by means of a four-pronged connector. The leads from the cell to the connector were shielded. Bridge Balance Indicator. The bridge balance indicator used was a simplified model of the type described by Garman and Kinneq (2). The circuit of thr bridge halance indicator is given
1592
ANALYTICAL CHEMISTRY
in Figure 2. The sensitivity is sufficient for the operation of this instrument, an unbalance of about 200 microvolts being visible. Power Sources. The input from a Terman oscillator to the bridge was passed through a cathode follower stage to assure less than 15% variation in voltage for the largest change in bridge im edance. The input was 1.3 volts a t 1000 cycles. I t was f o u n t t h a t with bridge input var ing between 1.0 and 1.5 volts, thermistor characteristics variezby less than 0.027,. At 2 volts and over, the characteristics were very sensitive to input voltage, owing to the greater power dissipation in the thermistor. The oscillator and bridge balance indicator were operated from a standard type power supply with regulated outputs a t 150 and 300 volts.
Table I.
Potassium Chloride
-
Solution
Kormality (Calcd.)
1
0.08860
Measured Values Room Temp. (23' C.) 180 c. 330 c. 0.0886 0.0887 0,0887 0,0884
0.0887
0.0885
0.0887
2K
2
O,OQ506
0.0950 0.0949 0,0950 0.0949
0.0950 0.0951
0.0951 0 0952
3
0.10000
0.1000 0,09993
0.0999 0.1000
0.1001 0.0999
4
0.10476
0.1047 0.1049
0.1045 0.1047
0.1048 0.1049
,4*+1bov J 0.10984 0.1099 0.1096 + lbOV 6
I
a ai
0.11343
0.1100 0.1100 0.1097
0,1099
0.1099 0.1099
0,1138 0 1136
0,1133 0.1129
0.1134 0.1133
Table 11. Potassium Dichromate Solution O K!
Xormality (Calcd. or Given)
Circuit of Bridge Balance Indicator
Instrument Characteristics. The warm-up time for the instrument is 5 minutes. The drift of the bridge balance indicator was 3.5 divisions in the next 15 minutes, but this is not enough to mask bridge balance settings. The drift in the next hour was a matter of 8 divisions. A check on two separate occasions of the effect of power dissipation in the thermistor showed that the change in normality readings was no more than 1 part in 1000 over a period of slightly more than 20 minutes, many times more than the time needed for a set of check readings on a solution. Procedure. Switch on the instrument. Set the potentiometers for the electrolyte to be determined. Rinse the cell with the standard solution and fill it with a sample of the standard. Set the normality scale for the standard value. Connect the cell to the bridge, maintaining a constant pressure on the dip cell in its cup. Balance the bridge alternately with decades and Kagner ground until maximum current is read on the bridge balance meter. This will be the decade setting to be used for subsequent measurements. Should the temperature change by more than 7" C., recalibrate. Remove the cell, rinse, and fill with the unknown solution. Connect the cell to the bridge, maintaining pressure on dip cell. Balance the bridge with alternate adjustment of the Wagner ground and normality scale. At balance read the normality of the solution directly from the scale.
l Y a C.
32-33'
C.
1
0,0900
0 0901 0.0900 0.0902
0 0900
0,0901
0.0901 0.0901
2
0.1000
0.1001 0.0999
0.1000 0.0999
0.1002 0.1001
3
0.1050
0.1051 0.1050
0.1051 0 1049
0.1030
4
0.1100
0.1101 0.1101
0.1100 0.1099
0.1102 0.1100
0.0944 0.0946 0,0945
0.0944
J
Figure 2.
Measured Values 16' or
Room t r n i i i .
0.1102 20
0.0945
0.0946
18
0.0924
0.0923
the temperature compensation test a little more severe, the meter was calibrated at room temperature only and the actual determinations were made a t as much as 10' C. off room temperature. The instrument in its present form is capable of a precision of 1 part in 600 for the temperature range 18' to 33" C. and the concentration range 0.09 t o 0.11 N . K i t h the building of a more permanent glass type of cell, this instrument should be capable of the 1 part in 1000 precision desired for analytical purposes and be applicable to a wide range of volumetric reagents. LITERATURE CITED
RESULTS AND DISCUSSION
The results obtained with the instrument are presented i n Tables I and 11. The solutions used were made by weighing the chemical substance and dissolving in 500 ml. of distilled water at room temperature. Two dichromate solutions were obtained from another department. Check values in the tables were determined on different d q s over a 2-rreek period, and are generally the average of two determinations. In order t o make
(1) Becker, Green, and Pearson, BeZZ System Tech. J., 26, 170 (1947). (2) Garman and Kinney, ISD. ENG. CHEY., ANAL. ED., 7, 319
(1935). (3) Shedlovsky, T., "Techniques of Organic Chemistry," Vol. I, Part 11, 2nd e&, New Tork, Interscience Publishers, 1949.
RECEIVED for review March 14, 1952. Accepted August 16, 1952. Based on a thesis submitted b y Alfred bl. J'ogel in partial fulfillment of the requirements for the degree of doctor of philosophy at New York University, June 1950.
