K. Hi c k m a n a n d C. R. Sa n f o r d, Eastman Kodak Co., Rochester, N. Y.
Fi g u r e 1 . Di a g r a m o f Di r e c t Me c h a n i c a l Ti t r a t i o n
The means chosen for securing the performance is illustrated in Figures 1 and 2. The first requisite, a timing unit to control the sequence of events, is provided by bulb A and appendages (2). When the bulb, which is fed with water or the unknown (dilute solution) under approximate control from tap 7i, has filled to level c, the solution passes over siphon C, loading the mercury column, D, which completes
T
H E paper industry has a very real need for a recording titrator, for a device which will determine the total acidity of alum baths, wash waters, etc. The present potentiometric recorders do not entirely meet the need, which is for an indication of reserve acidity and not for the potential of hydrogen ions. Further, it is found th at total acidity and potential are not simply or constantly related to one another under working conditions in a paper mill.The problem has been approached in two ways: directly, by the mechanical manipulation of solution volumes; and indirectly, by the diffusive mixing of parallel liquid streams.
Di r e c t Me c h a n i c a l Ti t r a t o r
A repeating cycle has been secured which comprises the following operations:
(а) A sample of standard volume is withdrawn from the unknown liquid.
(б) The sample is discharged into a reaction vessel together with a suitable quantity of indicator solution.
(c) The mixture is observed by an optical device which id) Controls the addition of the second component, the estimating fluid, in volume sufficient to reach neutrality, and
(e) Activates a pen to record the volume on a chart.
(/) The titrated solution is discharged to waste, the chart moved to a new position, and
(g) The cycle repeats.
Fi g u r e 2 . Vi e w o f Se t- Up o f Ti t r a t o r
a circuit through the electrode, E. The current actuates a magnetic valve, F, which allows the contents of the re
action vessel, G, to pass to waste. Soon after the emptying of G, bulb A should be full enough for its contents to siphon rapidly down tube H, unload mercury column D, and refill the reaction vessel. During the passage of this unit volume of fluid, a constant and repeatable suction impulse (nega
tive pressure X time of flow) is exerted a t each point in the column, notably a t points I and J , from which tubes communicate with constant-level reservoirs of reagents.
Through one tube a chemical color indicator (phenolphthalein, methyl red, etc.) is imbibed. The other tube is used only when pure water is fed to bulb A, and its purpose is to adm it a predetermined quantity of the liquid to be titrated. Thus, two general levels of solution strength can be manipulated,
66 A N A L Y T I C A L E D I T I O N Vol. 5, No. 1 the side arm accommodating
liquids containing from about 2.6 to 80 per cent of reactive material, the bulb being re
served for more dilute solu
tions.
The reaction vessel, G, is in two parts, a large bulb, g, and a smaller one, g', which communicate with one an
other by the centrally fixed lower tube, K , and the ec
c e n t r i c a l l y placed return tube, k. In g', the stirring paddle, rotated by the motor, L, is stopped temporarily through relay I, which is o p e r a t e d in tandem with valve F each time the vessel e m p tie s . The solution is monitored by the 100-w att projection lamp, M , and the
F i g u r e 3. D i a g r a m o f Re- light-sensitive element, A .
c o r d i n g M e c h a n i s m Since it is a change of inten
sity which is being observed during titration, a way m ust be devised to make Ar inoperative when the vessel is empty and is thus in its most transparent condition. In lieu of a mechanical shutter, the larger bulb is allowed to serve as a lens when full, concentrating the light from M on to N which otherwise remains relatively dark.
The cycle of operations is now continued by the electrical train in connection with N . Leaving for the moment the exact nature of the receiving element, we m ay assume th at the action of light is to generate a current sufficiently large to operate a relay. A fraction of a second after G is full, the entrained bubbles rise to the surface, the stirrer starts and cell N provides an e. m. f. just sufficient to operate, through relays, a solenoid valve, 0 , and the pen of the
re-Fi g u r e 4 . Ar r a n g e m e n t o p Op t i c a l. Me c h a n i s m w i t h Ph o t r o n i c Ce i.l
corder. Valve 0 admits the standard titrating liquid from a constant-level supply, Q, through a calibrated valve, R, and a fine tube, S, to the smaller bulb, g', where it is rapidly dispersed into the main body of the solution. The mixing
lag is 1 to 1.5 seconds.
The admission of titrating liquid under standardized con
ditions allows us to suppose th a t time and volume become mutually convertible. Hence, by recording time of addi
tion with constant subtraction of 1.5 seconds, we record volume. The time measurement is accomplished by allow
ing a clock-driven pen to be actuated in series with the ad
mission valve, so th a t the moment the liquid enters the re
action vessel the pen starts traveling over the chart. The admission continues till a color change is reached, when the light, becoming partially obscured by the solution, ceases to provide the minimum actuating current, the titrating liquid
is shut off, and the pen returns to zero. The master flow through B is arranged so th a t the reaction vessel shall be emptied soon after the completion of titration, enabling the events to repeat.
R e c o r d i n g M e c h a n i s m . A Telechron clock motor with shaft rotating a t one r. p. m. is mounted, field magnet down
wards on a pivot, as shown in Figure 3. On the shaft is a small roughened wheel which can engage with the rubber facing of a quadrant, the opposite end of which carries the recording pen. The clock rests by gravity in its idle position a little to the left of the vertical, and is brought into contact with the quadrant by a lever and m agnet when the latter is energized during titration. The quadrant is weighted to return the pen to zero when the magnetic pull ceases.
The chart for the records is carried in a clock whose drum rotates once an hour or once a day. The records consist of a series of vertical lines (arcs) of lengths corresponding to the volume of solution addition. If the lines are drawn close together, their upper limits provide a curve of the varia
tions in composition of the unknown liquid.
O p t i c a l M e c h a n i s m . I t is plain th a t a gas-filled photo-cell and com
mercial amplifier can be adapted di
rectly to this service and, therefore, only three alternative devices which have been used successfully in the place of such a cell will be described.
The new cell marketed by the Wes
ton Electrical Instrum ent Corp., the photronic cell, has proved very satisfac
tory for titrations where detection is required of a color change visible to the eye. The diagram in Figure 4 shows the preferred arrangement. The cell is connected in series with a microammeter and a Weston contacting galvanometer, Model 30-H, 300 ohms internal resistance, 250 microamperes per mm. deflection. The controlling spring about the pivot is twisted so th a t the needle is held against th a t contact pillar which is not in use, requiring a comparatively heavy current to effect contact with the live pillar. (If this precau
tion is not taken the galvanometer m ay stick.) An adjust
able resistance, carried in the lamp circuit, is set so th a t contact is just established when the reaction vessel is filled with clean water. The output terminals of the galva
nometer are connected in series with a 6-volt battery and a Weston Mercoid relay, type 630, 6-volt, Series 118. The duty side of this relay operates the circuit for the solenoid titrato r valve and the recording clock magnet.
The detail adjustm ent varies with the nature of the titra
tion. When standard alkali is being run against unknown acid with phenolphthalein as indicator, a green screen (Wrat- ten filter No. 59) is used between the vessel and the photronic cell; 95 to 100 volts across the 110-volt lamp, yielding 175 microamperes for operating the contacting galvanometer.
Development of a pink color during titration reduces the current ultimately to about 80 microamperes, b u t the end point is considered reached a t 165 microamperes, and a t th at point the contacting galvanometer breaks the circuit.
M any solutions which are too discolored to permit titra
tion with the usual indicators transm it freely in the infra
red. The nickel wire bolometer described elsewhere (1) is responsive to long-wave radiation, and can thus be used as a monitor provided a suitable indicator is available.
The development of a colloidal precipitate has been found to be a simple way to absorb the infra-red, and the metals of analytical group 3 have been studied to discover an indi
cator for acid — > alkali titrations. Whereas aluminum and chromium salts are useless and iron salts poor, a mixture of ferric and aluminum chlorides gives a sharp end point.
Fi g u r e 5 . Cr u d e Ga s Bo l o m e t e r
January 15, 1933 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 67 From 1 to 5 cc. of the indicator solution, which consists of
30 per cent ferric chloride and 5 per cent aluminum chloride, are added to the titrated solution (250 cc.) by side tube I in Figure 1. At the approach of neutrality, the solution turns a deep brown and then becomes opalescent, a t which point the bolometer end of balance current decreases sufficiently
Fi g u r e 6 . Im p r o v e d Ga s Bo l o m e t e r
to actuate the relay chain, which comprises the same instru
ments as for the photronic cell.
The photronic cell, which operates directly and without amplification, provides sufficient energy to disturb a galva
nometer needle. The movement of the needle, which repre
sents only a fraction of the energy in the light striking the cell, suggests th a t perhaps the light could perform mechani
cal work without first being converted to electricity. The expansion of a black gas a t the moment of illumination would seem a happy means to this end, but black gas mixtures are difficult of attainm ent and manipulation. A piece of black paper in a closed flask offered promise as a substitute.
Light warmed the paper which warmed the gas in contact, and a movement was observable a t the meniscus (Figure
5). When the liquid in the U-tube contained much po
tassium chloride, ready to complete an a. c. circuit between two copper electrodes, the device would operate the titrat
ing unit in a crude manner.
The improvements necessary to make the bolometer inde
pendent of external temperature and pressure changes will be published elsewhere, but a modification suitable for repeti
tive operation warrants description a t this time. In Figure 6 the receiving surface is conveniently a sheet of black gelatin emulsion stripped off a fogged and developed photo
graphic plate. I t is cemented between two pieces of glass
allowing W in c h (0.16-cm.) clearance on either side. The air-tight flat vessel is connected in parallel with a rubber diaphragm controlling a sensitive electrical contact, and a breather consisting of a small U-tube having a constriction situated between two enlargements. One or two drops of a phlegmatic liquid (butyl phthalate 90 per cent, isoamyl alcohol 10 per cent) is placed in the breather. Between the near limb and the receiving chamber a wad of absorbent cot
ton is pushed to slow the movement of gas.
In operation, as soon as light of sufficient intensity im
pinges on the receiving surface the gas expands, moving the diaphragm into electrical contact. Any gas in excess of the minimum required passes out through the bubbler
Fi g u r e 9 . Ci r c u l a r Ch a i n o f Cu p s w i t h Ro t a t i n g So l u t i o n Di v i d e r
until the force is insufficient to discharge the last bubble against the surface tension of the phlegmatic liquid. There persists a slight holding pressure to maintain electrical con
tact. W ien the light is withdrawn or diminished slightly, the bubble recedes, contact is broken, and the breather then admits whatever air is necessary to establish equilibrium in the opposite direction. If the device is operated, say, every 2 minutes, the likelihood of serious change occurring in the room conditions during the interval is remote.
The bolometer will operate from a 100-watt lamp, run a t capacity, for a visual change such as phenolphthalein, turning from white to pink in front of a copper sulfate screen. I t will operate a t greatly reduced wattage with the ferric infra-red indicator.
In d i r e c t Vi s u a l Ti t r a t o r
The gradual mixing of two-solution streams to produce a color change a t some point on a graduated scale offers many attractions. In a preliminary experiment a porous tube (Figure 7) was fed under pressure with acid solution, while alkali and methyl orange were passed in a uniform stream outside. I t was thought that, a t a distance from the entrance representing the quantity of acid necessary for neutralization, the outer solution should change from yellow to pink. Actually, the acid oozes through the earthenware to form a streamline sheath of liquid which refuses to mingle completely with the outer alkali, and the sheath is colored a t its interface for its entire length. Inclusion of a fine glass rod spiral to com
plicate the path scarcely assists matters.
The next development involved passing one liquid through a chain of cups into which the other liquid was dropped from calibrated orifices, as shown in Figure 8. The color change
Fi g u r e 8 . Ci i a i n o f Cu p s w i t h In d i r e c t Vi s u a l Ti t r a t i o n
68 A N A L Y T I C A L E D I T I O N Vol. 5, No. 1 would occur sharply in one cup in a series of twenty, but only
when individual stirring was provided and the jets were kept scrupulously clean. The method was impracticable in this primitive form.
n o i d Un i t
A satisfactory instrument was constructed utilizing a cir
cular chain of cups and a rotating solution divider for the second reagent. In Figure 9 the chain of cups is shown built into the space existing between two concentric Koda- loid cylinders (S). The channel is divided into fifty com
partments which rise from a sloping spiral platform. The liquid is adm itted into the top pocket through a calibrated jet fed from a constant-level vessel, and flows from compart
ment to compartment, over one barrier and under the next, until it has traversed the entire chain, whence it flows to waste.
The second liquid, which should be the more dilute, is sup
plied, also a t constant speed, to a float which rotates in a central pool of water maintained in circulation by a jet buried beneath the surface. The float is fitted with short pendant
paddles which engage in the slip stream w ithout being directly hit by the jet. From the float the liquid is discharged by a distributing pipe into the compartments, and, during any considerable period of time, is supplied to each compart
ment in an equal quantity. The tortuous path taken by the liquid insures mixing, and the point of neutrality is de
cided in one or two compartments, with a consequent error of not more than 2 or 4 per cent. A lamp is hung above the float chamber, and the compartments are numbered on the bottom in reverse writing so th a t the titration can be read in a mirror placed beneath the apparatus.
No t e o n So l e n o i d Va l v e s
The valves mentioned earlier in the paper are constructed cheaply from skeleton solenoids obtained commercially.
Type CR-95031 a. c. 1-inch stroke, 1-pound pull is adapted for the plunger to compress, or release from compression, a piece of soft rubber tubing, which thus forms the simple acid-proof body of the valve. The solenoid is then wound with wire of a size appropriate to the voltage and purpose.
A typical unit is shown in Figure 10.
Li t e r a t u r e Ci t e d
(1) H ickm an, K ., J . Soc. M otion P iclu rc E ngrs., 17, 591 (1931).
(2) H ickm an, K ., Trans. Soc. M otion P ictu re E ngrs., 26, 37 (1926).
(3) H ickm an, K ., and H yndm an, D ., J . F ra n k lin ln st., 20 7 ,2 3 1 (1929).
Re c e i v e d A u g u st 6, 1932. C o m m unication 497 from th e K o d a k R esearch L ab o rato ries.
1 G en eral E lec tric C atalo g N o. 29.