Fpbruary, 1928
ISDL-STRI,lL A S D ELYGINEERING CHE-MISTRY
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An Electrical Solution-Mixing Device’” I(. Hickman and D. Hyndman E - i s r m s KODAK COMPANY, ROCHESTER, ?;. Y.
Electrical titration methods in general use employ At first it m a y seem :I> FTER the perfection of electrodes immersed in the reacting liquids and give t h o u g h there are very fmje!ectrical methods for indications of hydrogen or other ion concentrations. coinnion reactions from which following analytical The indications have been used by various workers to a volatile material may be titrationi,J it was inevitable control automatically the mixing of the two reagents. liberated. This is not so. but t h a t t h e chemical engineer Such electrical controls may be described as operating if it mere it would still be should devise similar apparainternally. The present method uses external gaspossible to add gas-generattus for the automatic mixing eous indicators such as sulfur dioxide or ammonia ing materials as indicator-. of s o l u t i o n s . Valves conwhich it detects by an electric “nose” placed over the trolled by h y d r o g e n e l e c Thus the reaction reacting vessel. The variations in current actuate a trodes are now well known,4 valve, which limits the particular solution in excess and the patent l i t e r a t u r e a t t h a t moment. In this connection a special valve c o n t a i n s references to the has ammonia available for inmechanism has been devised which requires so little pouring together in equiradicator purposeq. If sulfuric energy for actuation t h a t no amplification or relays are lent proportions alrnost every acid and ammonia solutioii. required on the electrical circuit for the nose, even kind of liquid. are run into the mixing pot. I t is apparent that an e l e ~ though thousands of gallons of solution be handled the acid being independently each hour. The device is useful both in acidimetry variable in volume and colitrode placed in a solution for and in oxidation-reduction reactions, particularly with the purpose of exerting concentration while the amrnoni.i complex mixtures, since only the chosen volatile trol 1s really a n electrical subis controlled by the titrating constituent can effect the control. stitute for a chemical indiunit, then ainnionia will lie checked a t the moment :I cator. Indicators are broadly of two types, internal and external. Alethy1 orange used for trace of SHa gas finds its way to the water feeding the CfJllthe ordinary acid-alkali titration is an example of the former; ductivity cell. The iiiore coniniun reaction ferricyanide dropped on a white tile for iron estimations is a n example of the latter. T o the best of our knowledge the inH2S04 2KaOH = Na2S04 2H20 dicators used in electrical titrations, either to record or control, evolves no smell, but ammonia niay be added in minute have necessarily been of the internal type-the electrode has quantities to either solution and, being a weak base, will be been placed in the mixing vessel. The present communication the last to be neutralized, thus providing the necessary indidescribes a n electrical titrating or solution-mixing apparatus cator vapor. which works externally and for that reason ekapes certain An indicator working on the acid side is sulfur dioxide. -4 limitations inherent in the ordinary method. I t has, of trace of sulfite added t’o the alkaline reagent liberates the gas course, other limitations of its own. on becoming acid, and this is exceedinqly efficient in activating the conductiTity cell. “Electric Nose” The method has been found useful in oxidation-reduction I n popular language, we employ a n electrically senqitive reactions. I t may be necessary! for instance, t,o supply “nose” and arrange that a smell is developed or made to cease exactly equivalent’ amounts of ,sulfur dioxide, chlorine, broduring the reaction. More explicitly, one of the reactants or else the product of the reaction must contain a volatile or gaseous material which when dissolved in water will render it conducting. It is then possible to blow air or inert gas through the mixing pot, bubble this through water, pais tlie water into a conductivity cell, and allow the change in conductivity as the water begins or ceases to become saturated to control the reaction. The essentials of an apparatus to perform such a n operation are few. I n Figure 1, pipes A and B, carrying the solutions. discharge intocthe mixing vessel, C, and thence to their destination via D. A stream of air from E conireyq the indicator gas by way of F through the water in G, which then trickles into H . H carries the platinum electrodes. which are in series with a supply of current and a control valve, K , or relays and xalve K which limits the inflon- of tlie gaq-producing solution.
A
+
1 Presented before t h e Division of Industrial and Engineering Chemistry a t t h e 74th Meeting of t h e American Chemical Society, Detroit, Mich., September 5 t o 10, 1927. 2 Communication No 321 from t h e Research Laboratory of t h e E a s t man Kodak Company 8 Clark, “Determination of Hydrogen Ions,” Baltimore, 1922, Kolthoff and F u r m a n , “Potentiometric Titrations,” Xew Pork 1916 Cranc on, U S P a t e n t 1,341,361 (May 1920) Edelman, L S. Patent 1 3 4 1 790 (June 1, 1920)
Figure I-“Electric
+
Nose’’ for Mixing Solutions
mine, hypochlorite, etc., while keeping the main bulk of the mixture decidedly acid or alkaline, a condition making ordinary titration difficult. If it is desired to destroy hypochlorous acid from waste bleach liquors with the most economical expenditure of thiosulfate, the gas titration method can be employed excellently. The air containing a trace of chlo-
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Vol. 20, No. 2
saturated with the indicator vapor to approximately the same extent as the original mixing-tank effluent and passes into the cell, R. The capacity of this cell is so small that its contents are changed sufficiently every few seconds. It is made from 3/16inch Pyrex glass tubing and contains two parallel strips of fine platinum gauze I/* inch wide and ll/z inches long with the ends joined to wire and sealed through the glass walls. Note-Pyrex is reputed t o give bad seals with platinum. This may be true for delicate physical experiments, but the joint has been found water. tight and durable for the present purpose.
The outflow tubes, T, are arranged so that the water trickling into the cell just comes to the top of the electrodes. Figure 3-Device
for Alkali Controlling Flow of
rine saturates the c o n d u c t i v i t y cell water. H e r e t h e chlorine is oxidized t o hypochlorous Figure 2-Device for Adding Extra Alkali acid a t one pole and a t the other reduced to hydrochloric acid and the conductivity of the water rises accordingly. A reaction which is controlled excellently by the vaporelectric scheme is the neutralization of acid effluents in the presence of thiosulfate. Here sulfur dioxide is the indicating gas. I n the complete manufacture of photographic film there are rejected large quantities of sulfuric acid from cottonnitrating, alkaline developers from &-processing, and thiosulfate solutions from exhausted fixing baths. If these three liquids are discharged into a common sewer with the acid in excess, not only is sulfur liberated from the thiosulfate, but an odor of sulfur dioxide finds its way into the air. It has therefore been found convenient to augment the mixing by adding just sufficient extra alkali according to the following plan. Addition of Extra Alkali The extra alkali, the spent acid, and the alkaline hypo solutions are all discharged into a small mixing pot, A (Figure 2), by the pipes B, C, D. The liquids come together with such force that no mechanical stirring is necessary to give good blending. The mixture then flows out into a pipe, F, so large that the stream never fills it but merely falls with much splashing to a variable level, G, determined by the bulk of material being handled. The air in this tube, which of course enters a t E, is therefore saturated with the effluent and bears a proper proportion of the indicator vapor if any be present. The construction of the tubes H and K is such as to eliminate splashes from air leaving by L. This comprises the saturator unit. The detector unit consists of a Venturi water pump, M , discharging to waste by N a n d by-passing a thin stream by way of the needle valve. P. into the sDiral column. Q, up which 'it sucks the vapor-laden air from L. Water passing down Q becomes Fi$ure 4-Solenoid
Control of Alkali Flow
At this stage in the construction many experiments were carried out to devise a simple and robust method of controlling the extra alkali flow with the small current available from the cell. The current might be used (1) directly, (2) to actuate a relay, or (3) after thermionic amplification. Thefirst course hasgenerally been found inadequate, the second is reliable but gives only on and of control and cannot readilv be made to show hour much. Furthermore. relav apparatul contains iron, and iron rusts in the atmosphere i f damp acid-soaked basements. The third alternative was never considered owing to the necessity for skilled maintenance. Recourse was therefore made t o the direct utilization of the current in spite of its apparent inadequacy. With the tap water available the cell had a resistance of about 2000 ohms, falling to one-twentieth of that amount with about 0.1 per cent sulfur dioxide solution in the saturating tube. With such a high resistance it was assumed that there was lithe danger of serious electrical leakage if the cell were connected directly to the 110-volt house mains. This proved correct, for standing on a damp concrete floor in shoes saturated with dilute acid, no shock was felt on touching the water connection or the wet glass work. There was thus available energy with a zero value of 5 watts, increasing up to a maximum of 100 watts. T o obtain sensitivity, however, the apparatus must function when the conductivity merely doubles. The first successful control
n
TOWUIt.
I
u
Tipping Device
W Figure 5-Arrangement for Utilizing Rejected Liquid
February, 1928
INU USTRIAL A .VU EXGINEERIAVG CHEXISTR Y
was ina.de with the aid of a sinall '/jshorsepower Universal motor wired in series with the cell and the 110-volt alternating current supply. The motor was set vertically, with a propeller iastened io its shaft working in a small sump conuected with the alkali tank, the level of which was maintained constant. The 5 watts of energy resulting from the zero conchict.ivity just kept the motor t.urning, any additional current speeding it up and causing alkali to be pumped in varying degrees to the mixing box. The scheme is shown in Figure 3. B r u s h trouble and corrosion of the armature windings led to a s e a r c h for a simpler solution to the problem. A solenoid wound with enough No. 30 cottoncovered copper wire to possess a resistance of about 1000 dims l ~ a s built nith the idea of actuating a drop valve or conical plug in the a l k a l i - s u p p l y pipe. This worked well wit11 direct current, hut the detecting cell became fouled with deposits on the electrodes, a n d bubbles of gas altered t h e r e s i s t a n c e spasmodically. On altern a t i n g c u r r e n t , even with the softest of iron cores, very little attract i v e force N R S d e veloped. It was determined, however, to persevere with the solenoid using alternating current and to devise a virtually frictionless valve. This Figure 6-Assembled U n l t has proved successful and apparatus such as will now he described is being used on a works scale in the Eastman Kodak manufacturing plants for ditkrcut purposes. Let us suppose that t.here is an indefinite supply of a certain liquid flowirig to waste and that we wish to partition off a variable amomit for use. We can allow the whole stream to tumble into a hollow drum (Figure 4) pivoted axially so that it may be rotated in perfect balance through a few degrees. We can allow the stream to escape from the barrel by either or both of two openings having short delivery pipes disposed radially. Because the streams leave radially, they exert no turning moment on the drum, however unequally they issue from the openings. It therefore requires no effort to tip the drum (other than that absorbed by bearing friction) no matter in what proportion the stream happens to be divided. If a lever on t,he drum is connected with the core of a solenoid actuated by the vapor detector, solution will be deflected to or from the mixing- box whenever the water in the cell changes conductivity. Let us suppose further that it is not economical to let the rejected stream in Figure 4 run to waste. We can obviate it very simply as follows: The rejected portion is allowed to fall into a small shallow tank (Figure 5 ) , in which re& a float actuating a valve controlling the i d u x into the tipping drum. From thefloat tankaverysmallstrertmisby-passedtothemixing box. When the partitioning apparatus is started the large
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Nos-Perhapa a twentieth part 01 that which will be needed ln the mixing bur. This small pozticn is t h e only quantity not controllable by the tifintor s s d represent3 the minimum below which the npparettus will not shnt down automatically. I t i s easy to arrange that it is lese than sngthing demanded in practice.
stream entering the tipper mostly goes to waste and therefore quickly raises the float valve in the tank. The supply to the tipper is at once limited so that the amount not goiug to the mixing box is exactly equal to the amount by-passed. Since the control stream and the by-pass stream are both used in neutraliaat.ion, nothing is wasted. When t.he demand on the t i p p e d s o l u t i o n fluctuat,es, the amount. sent to the float taiik also v a r i e s and the stream sent to t.he tipper becomes adjusted to n new value hy the float salve. An actual unit coinnrisinr: the s a t u r a t o r . A, deikctor, II;and tip: Figure 7- Detail of Tipper per, C, mounted in a &tical wooden tray 5 by 2 feet ready for installation hut without pipe connections at D,D'>and D",is shown in Figure 6. A celluloid model of the tipper drum is shown separately in Figure 7. The only moving parts-the core of the solenoid and the fulcrum of the tipper-move in oil. The coil box is filled with transformer oil and the knife edges rest in oil troughs. The tipper and box are of monel metal. The saturator tube is 2 inches in diameter and 30 inches long and accommodates 1000 gallons of alkali a day. I n building larger units we keep the detector and solenoid the same size, scrap the saturator, and supply the detector with a part of the compressed air used to agitate the mixing pot. There is no difficulty in swinging a very much larger tipper. Although a solenoid operating off 80 cycles alternating current exerts only a small pull, it does it in a very interesting mamer. First, it is trembling all the time from the current fluctuations, and this removes most of the remaining friction from the tipper hearings. Then again, it becomes increasingly self-choking as the iron enters the core, so that if at any time there is a short circuit in the detector, the iron is sucked in fully and so little current passes that the coil does not get
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Figure 8-Applicatinn
of Tifratiun
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INDUSTRIAL A X D EXGIXEERING CHEMISTRY
perceptibly warmer than when working normally. Serertheless, we run the cell in series with a 60-watt lamp as a protection on the lead which does not pass through the coil. The weight of the iron core and the zero pull of the solenoid are balanced by a counter weight on the tipper. Moreover, we have assumed that the conductivity of the water feeding the Venturi pump and thence the cell is of a constant and negligible order. I n the Great Lakes region of America this is a safe assumption. Where, however, the water supply is not so pure and is variable during the day, it is necessary t o replace the counterbalance weight by another iron core actuated by a solenoid and compensating cell fed with a second stream of water. Only the added conductivity conferred by the indicator vapor will then be recorded. This double scheme is capable of an interesting application. Dilute solutions of two gaseous materials such as ammonia and sulfur dioxide may be mixed, a saturator and detector
5'01. 20, KO.2
being coupled with each cell. I n series with one is an absorption tower carrying alkali, in the other a wash bottle holding sulfuric acid. The one chain allows ammonia only to pass, the other, sulfur dioxide. Thus, perfect balance of the tipper is secured during variation of the load (Figure 8). We are using the scheme successfully for other reactions and have considered it advisable to seek patent protection. It is not possible to give definite figures with regard to performance. If the mixing pot is too small or too large. or the water stream feeding the conductivity cell is out of adjustment, the tipper will oscillate too far in each directiou and cause alternate over- and under-neutralization. With correct adjustment, which is very easy to obtain, the effluent. colored with phenolphthalein for acid-alkali reactions, or permanganate with oxidation-reduction reactions, will fluetuate between colorless and faintly pink. Caugnt in a large tank, the effluent of several hours is as nearly neutral as the product of a laboratory titration.
A Hardness Tester for Rubber' Erle C. Zimmerman and R. W. Brown THEFIRESTOXE TIREA N D RUBBERCOMPANY, A K R O N ,OHIO
ARIOUS forms of instruments have long been in use for measuring the hardness of vulcanized rubber. This use has undoubtedly been more or less extensive, but hardness has been rarely mentioned in the literature on rubber. Some of the earlier instruments were not direct-indicating, could not be operated by hand, and required the preparation of special samples. The first hand-operated instruments were a step in simplification, but were objectionable because of a low degree of accuracy and sensitivity. In attempting to overcome the objectionable features of these instruments, an instrument of improved design was developed u-hich has been i s use for several years and found to answer all the requirements satisfactorily.
V
Development of Penetrometer
Several instruments constructed to measure the hardness of vulcanized rubber are shown in Figure 1. The one a t the extreme left was originally developed for nieaquring plaqtic flow, but was later found adaptable in measuring hardness. The two instruments in the center of the illustration were developed in an attempt t o secure a portable instrument for the practical measurement of hardness. but they are limited somewhat in accuracy. The instrument at the right of the illustration, with its spring cover at extreme right, represents the first attempt by the authors to correct the difficulties experienced with previous instruments. All these instruments operate on the same fundamental principle-i. e., the application of a load upon a point arranged t o penetrate the rubber, the hardness of which is being determined, with an instrument dial indicating the amount of penetration. Obviously, to secure accuracy the applied load must be kept constant and a t a predetermined value. Also, the shape of the penetration point must be accurately maintained. In designing their instrument, the authors chose values of 1, 2, and 3 pounds, or 500, 1000, and 1500 grams, standardized the penetration point as a semi-sphere, 8/61 inch or 1.25 mm. radius, and made provision to measure the pene1 Presented before the Division of Rubber Chemistry at the 74th Meeting of the American Chemical Society, Detroit, Mich., September 5 to 10, 1927.
tration in thousandths of an inch or hundredths of a millimeter with 0.100 inch or 2.50 mm. maximum penetration. These values were selected from a number of different value, tried out and found to cover satisfactorily the range of hardness ordinarily encountered in vulcanized rubber compounds. Developments to date have resulted in instruments whose readings repeat to a high order of accuracy, and are who1 y interchangeable. Means for readily checking the zero reading and for determining the load on the penetration point greatly assisted in securing uniformity between instruments. In the actual construction of such instruments, it has been found necessary to make the spring relatively long so that the change in load between minimum and maximum penetration is negligibly small. This feature constitutes one of the very serious faults with the early instruments. The improvement made in this respect is shown in the in
