INDUSTRIAL AND ENGINEERING CHEMISTRY
290
uniformly advanced by a second operator. The blast flame is so adjusted that the outer brush is tangent to the mandrel and the tip of the inner cone just touches the glass rod. When a spiral has been drawn the Pyrex rod is quickly withdrawn to part the glass. The mandrel is removed by unscrewing clamps A and B, and the spiral is broken away from the ring and slipped off. After replacing the mandrel and rod another spiral can immediately be drawn. One critical adjustment is necessary in the position of the Pyrex rod. The elevation from the horizontal makes little difference, but it is essential that the longitudinal axis of the rod intersect the axis of the mandrel and be about perpendicular to it. Using this method a uniform spiral 35 cm. long can be drawn, removed from the mandrel, and the apparatus reassembled ready for another spiral in about 4 minutes. Several suggestions have been made for breaking spirals into individual single-turn helices (1, 2, 4). The authors found that negligible waste resulted if the spiral were returned to the mandrel, and individual helices broken apart by twist-
VOL. 11, NO. 5
ing the blade of a spatula or other similar blunt instrument between individual turns. Nonuniform spirals are difficult to remove from the winding form and yield considerable waste upon being broken into helices. I n a typical operation 15 cc. of single-turn helices were obtained in 20 minutes from four 28-cm. spirals weighing 2.85 grams. Waste material amounted to 0.1 gram or about 3.5 per cent by weight. Spirals have averaged 5.9 mm. in outer diameter with an individual fiber diameter of 0.6 mm. A few typical examples are shown in Figure 2.
Literature Cited (1) Roper, E. E.,Wright, G. F., Ruhoff, J. R., and Smith, W. R., J. Am. Chem. SOC.,57, 954 (1935). (2) Stewart, W. W.9 IND.ENQ.CHEM.9 Anal. Ed., 8,451 (1936). (3) Wilson, C.D., Parker, G. T., and Laughlin, K. C., J . Am. Chem. Soc., 55, 2795 (1933). (4) Young, W. G., and Jasaitis, Z., Zbid., 58, 377 (1936).
Semiautomatic, Multiple, Electrometric Titration Apparatus MAURICE E. STANSBY, Technological Laboratory, United States Bureau of Fisheries, Seattle, Wash., G. A. FITZGERALD, Birdseye Laboratories, Boston, Mass.
An apparatus is described in which ten electrometric titrations can be performed simultaneously by one operator within nearly as short a period as is required for a single titration. The burets are controlled by solenoids and the progress of the titration is followed by a series of colored lights on a control panel. While the apparatus was designed primarily for use in a fishfreshness titration, it can be used for a wide variety of potentiometric titrations. When applied to the determination of the freshness of fish, the apparatus enables a single operator to conduct freshness tests on a mass scale which would require six to eight operators using the ordinary singletitration method. A practical application foreseen by the authors is the predetermination of the freshness of all fish landed on the Boston Fish Pier to enable sale price to be based upon quality.
T
HE electrometric method for determining the freshness of fish, as proposed by Stansby and Lemon (6),was
studied further by Fitzgerald and Conway (1) to determine the practicability of its use in the commercial grading of fish. These studies showed an excellent correlation between freshness as indicated by electrometric titration and organoleptic tests conducted by expert fish buyers of long experience in judging the quality of fish. It was apparent, however, that if the method was to be applied in industry, certain
AND
modifications would be required to permit the handling of a considerable number of samples simultaneously. I n commercial practice, data on a large number of samples taken from different fishing vessels, and from different sections of the hold of each vessel, must be availabIe within a relatively short period. Accordingly, a multiple-unit apparatus has been constructed which allows an operator to handle up t o 10 samples a t a time. The apparatus is suitable for making a wide variety of potentiometric titrations and hence is described here in some detail.
Description of Apparatus The circuit consists essentially of 10 sample titration halfcells connected individually, one after the other, by means of an automatic switching arrangement through a galvanometer to a reference electrode. The principle employed is that of Treadwell and Weiss (6),whereby the reference half-cells contain a solution having a p H identical with the desired titration end point, a t which the galvanometer deflection will be zero. The automatic switch connects the titration cells into the circuit successively a t 3-second intervals. Thus, a galvanometer reading is obtained for each particular cell once every 30 seconds, and the progress of the titration followed accordingly. The presence of any one cell in the circuit is indicated by one of 10 flashing amber lights on a control panel. The titration burets are manipulated from the control panel and the flow of acid is controlled by solenoid cutoffs. When an end point for any cell is reached, as indicated by a zero deflection of the galvanometer a t the instant the cell is cut into the circuit, the operator can throw a switch which cuts off the corresponding buret. At the same tima a warning red light turns on, indicating that the particular buret has been turned off. A general view of the entire apparatus is given in Figure 1.
MAY 15, 1939
ANALYTICAL EDITION
291
operated burets, and from the electrodes, enter the panel circuit through the 4 radio tube sockets, X. The automatic selector switch, shown at the extreme right of Figure 3, consists of a 2gang, rotary, 10-point switch. One gan makes contact with each point for 1/10 o$ the rotational eriod, and is used for connecting the amger lights, E, into the alternating current circuit. The other gang connects the titrations into the galvanometer circuit. In this case, however, only momentary contact is made, so as to connect the electrodes to the galvanometer for just sufficient time to give a satisfactory deflection. This adjustment is somewhat critical, since continued contact increases polarization of the electrodes, while insufficient contact reduces the sensitivity of the galvanometer, and the best adjustment must be determined on the basis of experience. The switch is rotated by belt drive to a set of cone pulleys on shaft W ,from a Merkel-Korff motor and gear-reduction unit No. S-615, which is mounted on one outside edge of the panel case. The 110-volt, alternating current power for FIGURE 1. GENERAL VIEW OB TITRATION APPARATUS the apparatus is distributed to the rotary switch motor, the control panel alternating current circuit, and titration assembly b means of two double The control panel is shown in Figure 2. The main galvanomelectric outlet sockets, connected in parallef one being mounted on eter, A , at left center of the panel, is located centrally, with each end of the panel case. By using this system a flexible respect to the various lights and switches involved during the arrangement is attained, so that by removing the plugs from the course of the titration. The 10 toggle switches, G, control the solenoid buret cutoffs, sockets and the pulley belts, the Bakelite panel can be removed. The titration assembly, shown in Figure 1, consists of 10 and also operate the red warning lights, F , indicative of comsolenoid-operated burets, a battery of 10 stirring units with suppleted titrations. The flashing amber lights are shown as E. ports for 10 sample cells, the electrode system, a potassium The green lights, D, are controlled by toggle switches C. When chloride connecting system including agar bridges and potassium any of these switches are in the off position (adjacent green chloride trough, and a Bakelite connection panel. lights off) the corresponding titration cells are completely The solenoid burets are constructed somewhat like those disconnected from the circuit, regardless of the position of the described by Shenk and Fenwick (S),but. differ in the following automatic switch. The apparatus is designed to permit alternate use of 2 reference respects: In the original Shenk and Fenwick burets the flow of reagent is stopped by turning off the solenoid, whereas in the electrodes. Connection to either electrode is made through present case the clamp is designed to turn on the flow of reagent toggle switch J , and amber light L or green light M indicates which is in the circuit. Toggle switch H connects the alternating current power to the control panel, and also turns on the power to the solenoid b u r e t cutoffs. Thus, all SOCKETS FOR CONNECTING CABLES b u r e t s can be o p e r a t e d simultaneously by switch H , U or individually by the proper switch, G. Toggle switch K , designated as the master switch, disconnects all cells from the @ SOLENOID TOGGLE SWITCHES (9 galvanometer circuit. This is @ RED SOLENOID LIGHTS provided to reduce the total time a cell is in the circuit 2 @ FLAJHING AMBER LIGHTS 9 0 during a t i t r a t i o n , t h u s GREEN ELECTRODE LIGHTS minimizing polarization, @ ELECTRODE TOGGLE SWITCHU The off position is indicated by red light P, and the on position by amber light N . AUTOMATIC The control panel is 0 equipped also with an auxilSWITCH SHAFT i a r y , m a n u a l l y operated, rotary, 10-point switch, U, and an auxiliary galvanometer, B. By depressing push button T, the main galvanometer is disconnected and replaced in the circuit by the auxiliary galvanometer. I n this case, the titration to be connected to the galva5 0 nometer can be selected manAUXILIARY ually by the auxiliary rotary REFERENCE @ OFF-ON @ CALVANOM LTER switch. Both galvanometers MASTER POWER E LECTRDDE are Leeds t Northrup, No. SWITCW SWITCH 2324-D, without mounting cases, RED POSH AMBER The automatic selector AMBER GREEN BUTTON LIGHT LLWT switch is mounted beneath LIGHT LIGHT the panel at W. Cable connections from the solenoidFIGURE 2. DIAGRAM OF CONTROL PANEL
m
A
0
000
000
INDUSTRIAL AND ENGINEERING_CHEMISTRY
292
FIGURE 3. WIRINGOF COXTROL PANEL when the solenoid is turned off. Also the tension in the spring is adjusted so that it is not necessary to reset the clamp manually in order to start the flow of reagent. The battery of 10 electrically driven stirrers is mounted on a wooden platform 130 cm. long. The stirrers consist of Monel metal rods with spiral sha ed paddles made from Monel metal wire and are fastened by iakelite insulating couplings to rods which are rotated by being geared to a horizontal countershaft, driven by a 0.125-horsepower electric motor. The beakers used for the sam le cells are supported beneath the stirrers on wooden shelves wiich in turn are supported by a rod and thumb catch. By releasing the thumb catch, the shelf ,pivots about the rod so as to lower the beaker from the rigid stirrer. Figure 4 shows a close-up view of stirrer, beaker, and solenoid cutoff. CJuinhydrone electrodes for both the sample an reference cells consist of 1 sq. cm. of platinum foil attached to 10-cm. lengths of platinum wire. The reference half-cells are contained in small vials fastened to a small wooden platform. The electrodes in the sample cells are held in place by means of the support, described by Stansby (4). The agar bridges from the 10 sample and 2 reference half-cells dip into a long wooden trough, containing saturated potassium chloride solution, extending the length of the apparatus. Connections from the electrodes and solenoids to the control panel are made a t a Bakelite connection panel. This panel which is 35 cm. long and 12.5 cm. wide, contains small radio-type plug jacks for the solenoids, and radio tube sockets for the electrode connections. Four different types of radio sockets are used, in order to eliminate any possibility of making a wrong connection. The connection panel can be seen in Figures 1 and 4. Contact between the control panel and connection panel is made by means of cables, having corresponding plugs a t each end.
VOL. 11, NO. 5
The burets are filled with the titration reagent and are held shut by pinchclamps. This is necessary because, as described previously, the solenoid-operated buret clamps are open when the current is off, and closed when the solenoid is energized. The 10, or fewer, samples are placed in position on the sample cell supports, and the electrodes and agar bridges are attached. If the operator is beginning a day's testing, the reference electrodes are also filled with fresh buffer solutions of the desired end points of the titrations. When the samples are in position and the abovementioned connections have been made, the alternating current power is turned on by means of switch H . If not already so, the master switch, K , is turned to the off position and is kept in this position during the titrations, except when actual galvanometer observations are being made, in order to minimize polarization of the electrodes. The solenoid toggle switches, G, are then turned to the on position (all the red lights, F,on). The electrode toggle switches, C , are also turned to the on position, this being indicated by the green lights, D. If less than 10 samples are being tested, the green lights corresponding to electrodes not in use should be turned off. The apparatus may now be considered in readiness for beginn-iig the titration. The automatic switch motor is turned on and the master switch opened while the violence of the galvanometer deflection for each of the samples is observed. In the fish titration and others involving systems fairly well buffered a t the end point, the violence of the galvanometer deflection is roughly indicative of the proximity of the end point; after some experience with the particular system, the operator will be able to estimate from the galvanometer deflection the a p proximate amount of reagent required t o reach the end point in each titration. The pinchclamps on the burets are then released and the flow of acid is started by turning off the alternating current power switch. The quantity of reagent added to each cell should be slightly less than that estimated as necessary to bring the cell giving the weakest initial galvanometer deflection to the end point. The
Operation The apparatus is capable of considerable ASSEMBLY FIGURE 4. CLOSE-UPVIEW OF TITRATION flexibility in manipulation, and since many different Droblems may be expected in the flow of reagent is stopped by turning on the alternating power field of e1ectrometric"titratio~sno one schedule of operaagain, since the solenoid buret clamps close when the solenoid tions can be recommended as most suitable for every problem. is energized, and the galvanometer deflections of the 10 samples Even in the fish titrations, it was found from experience that are again observed by of the automatic switching arcertain situations required modifications in the continuity of rangement. If none of the titrations is yet near the end point, the above procedure is repeated until one or more are practically operating procedure. The following procedure, therefore, at, or have reached an end point, as indicated by a very feeble or may be considered as meeting the average situation when zero galvanometer deflection. The process is then continued by determining simultaneously the freshness of a number of Samcontrolling the flow of acid to each cell bv means of the corples of fish. responding toggle switch, G , until all titrations have reached
MAY 15, 1939
ANAL
an end point. This is accomplished by alternately adding reagent to the respective cells and observing the cycle of galvanometer deflections, Often the last two or three titrations to reach an end point can be observed more conveniently on the auxiliary galvanometer. The connections are made by means of the manual switch, thus eliminating the necessity of waiting for a complete rotation of the automatic switch before each galvanometer reading. When all cells have reached the end point, the burets are read, the second reference electrode is switched into the circuit by means of toggle switch J, and the entire procedure is repeated. Adjacent sample cells-for example, 4 and S o f t e n require considerably different quantities of reagent to reach an end point. If the first cell should be far removed from the end point and the second one close, the oscillation of the galvanometer needle resulting from the violent deflection caused by cell 4 may be greater than the normal deflection that would be caused by cell 5. This situation can usually be anticipated and is taken care of by disconnecting the cell far removed from the end point, by shutting off the corresponding electrode switch, C, as will be indicated by the corresponding green light, D. When this is done, cell 4 will cause no galvanometer deflection when contact is made by the automatic switch, and the observation for cell 5 can be made without hindrance. If several cells are involved, the same procedure can be used, in which case the switches, C, corresponding to the cells most distant from the end points are turned off just before the automatic switch would have connected them to the galvanometer. I n case a very complicated situation arises, one cell may be observed on the auxiliary galvanometer, some cells disconnected as described above, and others observed on the main galvanometer. By means of this flexibility in manipulation, the operator can make the necessary galvanometer observations without any great difficulty, regardless of the order in which the end points are reached. I n using the apparatus for other titrations, it might often be more practical t o have the reagent added dropwise continuously from the burets, shutting off each titration when the end point was reached. Such a procedure is probably what would be expected normally, on the basis of the description of the apparatus, especially where the approximate amount of reagent cannot be anticipated. However, in the case of the fish titrations, where definite minimum titration values are always encountered, experience has shown that the procedure which has been described requires much less time for completing a series.
Applications While the apparatus was designed especially for use with fish, there is no reason why it cannot be used for numerous other titrations. It is, of course, of chief value where a large number of similar titrations are being run frequently, and can best be adapted to titrations which are fairly well buffered a t the end point. Some possible applications are to the determination of total acidity of various food products, free fatty acid determinations in oils, and many titrations where a color standard is used in titrating t o a definite PT value (Kolthoff and Furman, 2). Other electrode systems than the quinhydrone can be used if a fairly stable e. m. f. is rapidly attained. By using the 2 reference electrodes, two different types of titrations can be run simultaneously. It is also possible to make the apparatus completely automatic, so that the burets are shut off a t the end point without manual switch manipulation. This can be done by substituting a controlling potentiometer of suitable sensitivity for the central galvanometer. The output of this potentiometer would have to be connected through the rotary automatic switch to the solenoids on the burets. However, such
ON
293
an arrangement would greatly complicate the apparatus and add considerably to the cost. The total expenditure for parts for constructing the apparatus as described, including the automatic buret shutoffs but not the burets, stirrers, beaker supports, or electrodes, is about $175. A considerable portion of the equipment, such as the jeweled pilot lights, the step-down transformer for the lights, the toggle switches, etc., are standard radio parts, obtainable a t most radio supply stores.
Literature Cited (1) Fitzgerald, G . A., and Conway, W. S., Am. J . Pub. Health, 27, 1094 (1937). (2) Kolthoff, I. M., and Furman, N. H., “Volumetric Analysis”, Vol. 11, Chapters 4 and 5, New York, John Wiley & Sons, 1929. (3) Shenk, W. E., and Fenwick, F., IND.ENQ. CEEM.,Anal. Ed., 7, 194 (1935). (4) Stansby, M. E., Zbid., 10, 529 (1938). (5) Stansby, M. E., and Lemon, J. M., Ibid., 5, 208 (1933). (6) Treadwell, W. D., and Weiss, L., Helv. Chim. Acta, 2, 680 (1918). PUBLISHED with the permission of the Commissioner, U. S. Bureau of
Fisheries.
CORRESPONDENCE Standardization of 2,6-Dichlorophenolindophenol for Ascorbic Acid Titration SIR: Two papers appeared simultaneously in the ANALYTICAL (1, 3) purporting to disclose a new method for the standEDITION ardization of the redox indicator 2,6-dichlorophenolindophenol. An editor’s note draws attention t o the coincidence that Menaker and Guerrant publish their “improved method” virtually at the same time as the “new method” of Buck and Ritchie, and states that “priority for the published disclosure must be given to Buck and Ritchie.” Actually, this method (wherein the indophenol is caused to oxidize potassium iodide to free iodine which is then titrated with thiosulfate) was published several years ago (4) and appears to have been put forward by Dick (2) who was an associate of Tillmans. It is evident, therefore, that this method-which we have found to be thoroughly reliable-should be credited to Dick and not to the authors of either of the recent papers (1,s). For a comparison of details, the directions given in the earlier publication (4) may be worth noting: “To 10 ml. of dye solution add 3 ml. of fresh 10 per cent potassium iodide solution and 2 ml. of 32 per cent sulfuric acid, mixing carefully until the blue color has changed completely through red to yellow; add 60 ml. of water and titrate with 0.01 N thiosulfate.” It will be seen from this that Dick’s method is practically identical with those referred to above.
Literature Cited (1) Buck, R. E., and Ritchie, W. S., IND. ENQ. CHEM., Anal. Ed,, 10, 26 (1938). (2) Dick, H., dissertation, Frankfurt, 1932. (3) Menaker, M. H., and Guerrant. N. B., IND. ENQ.CHEM.,Anal. Ed., 10, 25 (1938). (4) Winterstein and Funk, in “Handbuch der Pflanzenanalyse”, ed. by G. Klein, Vol. 4, p. 1083, Vienna, Julius Springer, 1933. DOMINION LABORATORY DEPARTMENT OB SCIENTIFIC AND INDUSTRIAL RESEARCH WELLINQTON, NEWZEALAND
0. .. H. KEYS ~~-
