1 A STUDY IN CONDUCTIVITY MEASUREMENTS BY VIRGIL RICHARD SULLIVAN AND JOHN WILLIAM APPLING THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE IN CHEMISTRY COLLEGE OF LIBERAL ARTS AND SCIENCES UNIVERSITY OF ILLINOIS 1921 Digitized by the Internet Archive in 2015 https://archive.org/details/studyinconductivOOsull TABLE OF CONTENTS. I. General Introduction, p.l. II. Regulation of the Thermostat, p.l. III. Booth circuits and the Calibration of the Kohlrausch Bridge. pp.1-4, Diagram of Bridge and Commutator p.3. IV. Reconstruction of the Water Purifying Quartz Still, pp.4-5. V. Apparatus for Steaming out the Cell and Electrodes, p.5. VI. Determination of the Cell Constant of the Quartz Cell, pp.5-6. VII. Attempts at the Preparation of ultra Pure Conductivity Water. p.6. VIII. Bibliography, p.7. IX. Acknowledgment, p.7. . * ■ I. GENERAL INTRODUCTION. In undertaking this problem, the authors had in mind a contin- uation of some work carried out previously in this laboratory by H.J.Weiland, in which some very careful measurements were made of the conductivity of dilute solutions of potassium chloride, the in- tention in this case being to study dilute solutions of hydrogen chloride. For further information concerning the bridges used, the preparation of conductivity water and the prevention of contamina- tion of it by the air, etc. reference is made to this thesis. II. REGULATION OF THE THERMOSTAT . No conductivity work having been done here for some time, the apparatus as used by We Hand was found to be sadly in need of re- pair or replacement. Attention was first directed to the oil ther- mostat, using the ordinary mercury regulator and electric circuits with the relay. Some trouble was experienced in aa justing the ap- paratus so that the bath would maintain a sufficiently constant temperature over long intervals of time. Instead of using a plati- num wire to make contact with the mercury, a sharp pointed iron rod was finally substituted. The point was carefully blued, and after being used for some time appeared to be unaltered. This eas- ily furnished for several hours at a time a very close temperature regulation ( + 0.005°). After this the thermostat gave no trouble. A cooling coil, stirring apparatus, etc. exactly like that used by Weiland, was used. Special mention should be made at this point of the satisfactory use of a device reported by King (2) to protect the mercury contact in the regulator from oxidation. III. BOOTH CIRCUITS AND THE CALIBRATION OF THE KOHLRAUSCH BRIDGE. The circuits in the sound proof booth and those of the high . 2 frequency generator having been disarranged, some tracing of cir- cuits and re— wiring was found necessary. It was necessary to re- wind the drum of the Kohlrausch bridge, and to re-calibrate it, the data for which is given below: For R~ a resistance box was inserted and direct current was used from two dry cells across the ends of the bridge, R c = 5Q 30 70 20 10 R = 700 700 700 700 700 a = 69S.3 429.8 957.5 289.8 146.0 Si (Calc.) - 9489.5 9458.4 9532.5 9432.8 9366.0 ’• Equation used R _ b 4- E n Average value 9455.8 R a a. R c = 700 210 700 700 700 R = 10 10 35 40 55 a - 849.8 516.5 495.0 428.0 231.0 TP (Calc.) =9664.2 9637.0 9605.0 9582.0 9556.0 Equation used R _ b Average value 9608.8 Rq a _i£- This gives a total length for the bridge of just about 20,064 parts ( i.e., units of length). The following method of evaluating the total length of the bridge wire checked very well with the one just given: The resistance of the wire on the drum was measured, and found to be 12.52 ohms, the length of the wire being arbitrarily taken as 1003 units. The total resistance of the bridge, including extension coils, was 250.36 ohms, hence 250.36 x 1003 - 20,055' parts, being 12.52 apparent length of the bridge wire. For final values, the total length of the bridge was taken as 20,060 parts, divided as follows: ( Continued on Page 4.) 3 page, R is a standard resistance box, R is the cell, En and E are the extension coils to the Kohlrausch bridge (arms represented by a and b) , T is the telephone, G is the ground, N represents the leads to the high frequency generator, a' and b' are the two arms of the constant ratio bridge, and TV is the second lead to the telephone when the constant ratio bridge is in use. . 4 - 9454, E r - 9606, on toe arum = 1000. This calibration must be taken only as approximate, and. not final. It answered very well in the preliminary work. For the final measurements the intention was to use the apparatus as a "commutating bridge" and thus obviate the necessity for any very extensive calibration. The following simple scheme was devised for the convenient interchanging of the Kohlrausch bridge and tiie constant ratio bridge ( see the diagram on the preceding page): R- and are connected to the known re- sistance R, T^_ is one lead to the telephone, the other being at- tached to the middle of the drum of the Kohlrausch bridge and to the proper place on the constant ratio bridge, B-^ and are con- nected to the ends of the Kohlrausch bridge, R- and 0^ are con- nected to the ends of the constant ratio bridge, and R^ and Gj_ are connected to the high frequency current. It can be seen that by interchanging of the cup connectors on the commutator, either bridge may be thrown into the circuit separately. IV. RECONSTRUCTION OF THE WATER PURIFYING QUARTZ STILL. The repair of the quartz still for the final purification of the water presented the greatest difficulties, and even at the last was not very satisfactory in use. The two nichrome heating units used in heating the quartz flask were eitiier badly corroded or en- tirely burnt out. They were re-wound and embedded in a mixture of asbestos, silica, and bone ash, which could readily be worked into any desired shape when wet. Considerable care had to be exercised in drying this mixture with the current on, for the wire seemed to "rot" very easily and crumble to pieces. It was dried very slowly. Each unit had a resistance of about 20.5 ohms and they were connec- ted to the 110 volt D.G. line in series with an ammeter and a rheo- . » f 5 stat. Three amperes of current in the bottom unit was sufficient to keep the water hot while air passed thru the still, while with five amperes, the water distilled over, thus rendering the use of the upper heating unit optional. The purifying air train had to be rebuilt, and was modeled directly after the one used by Weiiand. It was found impossible to make the air compressor w ork, so finally recourse was had to the air line in the building. Several Drexel bottles, filled with con- centrated sulfuric acid, glass wool, sodium hydroxide, and two filled with cotton, were inserted in the air line before the train described by Weiiand. It was thought that this extra precaution would eliminate moisture, grease, and other undesirable constitu- ents, but the investigations aid not reach a point giving any de- finite assurance on this subject. V. APPARATUS FOR STEAMING- OUT THE CELL AND ELECTRODES. The apparatus for steaming out the electrodes is described by Weiiand. In order to avoid the use of gas, especially when it was desirable to steam out the apparatus over night, an electric heat- ing unit was built, and mounted in a asbestos wire-gauze. Number 18 ni chrome wire was used, enough to give a resistance of about 28 ohms, and the coil was embedded in a mixture of asbestos, silica, and bone asn, so arranged to hold a three liter round bottom Pyrex flask. Using this form of apparatus, very good results were ob- tained, even when used for considerable time. VI. DETERMINATION OF THE CELL CONSTANT OF THE QUARTZ C^LL. In order that the later work on the preparation of conductiv- ity water might have some significance, tentative determinations of the cell constant of the quartz cell were made, using an approxi— . . ' r 6 raately N/lOOO solution of potassium chloride with cell Number 16, whose cell constant was known* No attempts were made to determine this value with any degree of accuracy, because it was realized the cell would have to be repaired before actual work could be done with it, and this investigation was principally concerned with pre- liminary work, in some measure to prepare for later work. For this reason, it does not seem necessary to give any data upon these approximate measurements. VII. ATTI AT THE PREPARATION OF ULTRA-PURE CONDUCTIVITY WATER. Knowing Approximately the cell constant of the quartz cell, it was thought advisable next to start to prepare the ultra-pure con- ductivity water. The method and general procedure has been that outlined by Wei land. The first run was begun about march 15, 1921 and subsequently repeated several times. No encouraging results can be reported in any of tnese series because of the difficulties ex- perienced in working with the apparatus. The general conductivity still gave no little trouble because of low steam pressure and faulty valves, so that in several cases the purity of the water started with was questionable. Again the rotary air compressor (which was being used at that time) quit working with considerable regularity, and when the stream of purified air could not be forced thru the still, the experiment was useless. In addition, the quartz platinum seal of the quartz cell electrodes had broken loose, and attempts at repairing proved useless, so finally worm had to be suspended. In no case, in so far as it was possible to determine, was conductivity water of a purity (specific conductance) better than 0.25 x 10 reciprocal ohns obtained. It is regretted that the problem had to be abandoned at this . ' 7 indefinite stage, and it is hoped that it can be completed at some future time. VIII. BIBLIOGRAPHY . (1) Thesis, University of Illinois, 1917, H.J.Weiland. (2) Journal of the American Chemical Society, October 1920, p.2058. IX. ACKNOWLEDGMENT . The writers desire to express their thanks to Dr . G-.Dietrichson under whose direction the investigation was carried out. They also wish to thank other members of the department for their interest and cooperation during the past year's worK. I \