ANALYTICAL EDITION
September 15, 1941
B. The role of the propeller w ~ lbe l to generate fast-moving currents of liquid through the mixture. A propeller with a large number of blndcj operatinp xt high speed Giglit conreivahly crUc t h p liquid inru m m ~ ypart, and accomplish a degree of nixing. k : x 1 1 srtmcnt. however. nwdr enoueh nurlsrr t o serve m B mod driver. -The general iu6ffectivenessof the eight-bladed pro&ie; at 6000 and 10,750 r. p. m. was pronounced. The mechanical heat generated by its use was in nearly every instance the greatest (sometimes by 50 to 100 per cent) of the three, yet it appeared to whirl around in a generally ineffective manner. The propeller with four blades gives a siltisfaotow uerformauce. Even a good ~
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Acknowledgment The authors are indebted to I. Amdur for very helpful suggestions in banding the data.
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tical"impo2ance in large-scale a&arat;s. C. Impediments, whether points on the inner surface of the flpsk or nalli to ronsrrict the~flo\r,rrsulr in a reduction in etlrimcg. A very fine wrePii which suhdividrs the liquid into small onniclm ndiistj the rmrtion. but the entrxv rpauirrd to O ~ I W M P stirring apppratw of that'type is very mnch'greater &d the ratio of chemical to mechanical heat is less than in a properly designed flask.
Literature Cited (1) Brunner, E. J., 2.pfiysik. Chem., 47, 56 (1904). (2) Friand, J. A. N.. and Dennett, J. A., J. Cfiem. Sm., 121, 41 (1922). (3) Hershberg, E. B., IND.E m . Cwnr.. h t , . ED.,11, 170 (1939). (4) Huber, F.C.. and Reid, E. E.. IND.Em. CHEM., 18,535 (1926). (5) MUigan, C. H.. and Reid. E. E., Ibid.. 15, 1048 (1923). (6) Morton, A.A., IND.ENU.CHEM.,ANAL.ED.,11, 170 (1939). (7) Morton. A. A,. Olson, A. R., and Blattenherger, J. W., J . Am. Chem. Soc.. 63, 314 (1941). (8) Van Name.R. G., and Edgar, G.. 2.pfiy,sik. Chem.. 73,97 (1910). Connuanrronfrom the Research Laborstory of Orgsnio Chemistry. Mass* ohusetta Institute of Teohnology. No. 248.
Potentiometric Titration Stand Assembly LOUIS LYKKEN
AND
F. B. ROLFSON, Shell Development Company, Emeryville, Calif.
HE u e of electrometric titration methods has slowly bea laboratory practice. Although poten-
T
tiometric titrations have long been used by academic workers for special determinations, this t m e of analysis has found only limited application in many industrial laboratories because the apparatus has had t o be assembled largely from miscellaneous parts at hand. Generally, this resulted in a cumbersome assembly which was inconvenient and unwieldy to use in routine determinations. Also, expeneuce has shown . ... that the use of loosely assen ' ' * ' considerable part of the ope] nance. In designing the assembly described here, every effort was made t o produce a titration stand which could be used for routine as well as special determinations. It was recognized that a satisfactory assembly must he as easy t o use as the ordinary apparatus required for indicator titrations. The buret clamp, stirring motor, 1beaker cover, and electrode s u p port have been semipermanerttly attached to the vertical s u p porting rod. The table sup]iorting the titration beaker has been designed t o be the only eiasily movable part on the stand. The buret may be readily reinoved from ita support and the electrodes may be convenient ly removed and replaced. During two years of contin ued use at Emeryville, five such titration stands have been foiund satisfactory and convenient for routine titrations. They are durable, are easy t o maintain, are simple to operate, i-Lave a neat appearance and, although unitized into compact units, are sufficiently flexible for most electrometric titrations.
motor; the Eastern Engineering Company variable-speed stirrer, Model 1, has proved satisfactory. The motor and rheostat are conveniently mounted on the same support, as shown in Figure 3 Pencil- or stick-type electrodes me used throughout; whenever a salt bridge is used, contact is made with the titration medium
nes,
~~~~~~~~~~~~~~~~m~~~~~~~~~~~~~~~~ nical Laboratories, have been found ideally suited for use in the titration assembly. For convenience, metallic electrodes-i. e., Silver, Platinum, and tungsten-have been mounted, a8 shown in wim.r.?,,nF+, "~""~-~--"" .--. :~ 1-11,~ . . :.-1 ~' . ~~ 1 ~
APParatus A photograph of one farm of the assembly is given in Figure I and some details of constructiorI arc shorn in Figures 2 to 4. 'l'he customary "universal" clamps ~ S V Pbepn renlnwd bv metal connector-blocks containing holes of apnronrike size &d headless Uristo se1scrPwz. so ;tten,pt has%ee< made to use the same rnnnector-block for all p u r p o w. A modified thermometer clamp rcplwes thr custmury huret h older or clamp. A thick piece of uolidied IQkrlitc is used as D1 comhination electrode support, beaker cover, and buret-tip support. The titration vessel, which ,,-Axr- hnolm* nm a is a 250-ml. tall-form electrolyt... I_.I_., i. a..nnnd-l y.l Bakelite to a friction clamp. The glass, propuertype stirrer is supported and operated by a small variablespeed
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YY~rV.U'U
FIGWE1. TITUTIONASSEMBLYPEEPARED FOR NEUTULI*AII"N
rn Ill&%X,"Nb
Beckman Model 0 deatronic voltmeter and Beckman glass and oalome~ electrodes
8654
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 13, No. 9
METAL CAP : 518 IN. (1.59CM.IDIAM. .CEMENT SEAL
w
FILL WITH DE KHOTINSKY CEMENT
BAKELITE DISC 0 I
l
l
5CM. ]
Scale
-
HEAVY METAL WIRE
FIGURE 2.
FIGURE 3.
M O T O R AND
, / BAKELITE
hlETAL
ELECTRODE (left)
RHEOSTAT hfOUNTING (left)
AND M O V A B L E
AND C O M B I K E D
BEAKERS U P P O R T (Tight)
ELECTRODE HOLDER AND BEAKER C O V E R (Tight)
DISC
BRISTO SET SCRE
w
FIGURE 4. ELECTRODE S U P P O R T DISKFOR
0
5CM.
\ " " 4Scale SEMIMICROTITRATIONS
( k j t ) AND
SUPPORT
BLOCK .4ND BERETC L A M P (Tight)
September 15, 1941
ANALYTICAL EDITION
The assembly is made on any 1.25-cm. (0.5-inch) rin stand rod. The various metal parts are made of brass and su%sequently chromium-plated. This platin has proved satisfactory aa a protection against attack by the la%oratory fumes and affords adurable, neat finish. The apparatus may be readily adapted to semimicrotitrations, of 5- to 10-ml. initial volume of solution, by changing the Bakelite electrode support disk and using a special titration cell in place of the tall-form beaker. The Bakelite disk of Figure 3 (right) is replaced by the one shown in Figure 4 (left), in which the holes
655
are brought closer to ether. The modified disk has a small raised portion, 33 mm. in timeter, on the underside. The special titration cell is made from Pyrex glass tubing 34 mm. In inside diameter; it is sealed off flat a t one end and IS cut to give an internal length equal to 11.2 cm. The blades on the glass propeller stirrer are ground down to be 12 to 13 mm. in diameter. The regular Beckman electrodes and stirrer are adjusted so that they almost touch the bottom of the special cell when the latter is in position on the stand. The buret is made with a 15-cm. (6-inch) tip that has a 10- to 15-mm. offset about 12 cm. from the end tip.
Magnetic Stirrer for Use in the Cup Type of Moisture-Transfusion Apparatus HORACE K. BURR A N D ALFRED J. STAMM, Forest Products Laboratory, Madison, Wis.
T
HE cup type of moisture-transfusion apparatus is the
chief means used for determining the passage of moisture under a relative humidity gradient through paper, impregnated paper, film material such as cellophane, and thin sections of wood. Water, an aqueous solution of sulfuric acid, or a saturated salt solution in equilibrium with a specific relative humidity is oured into the bottom of a cup. The membrane material to e! studied is sealed across the top of the cup. The cup is then weighed and the loss or gain in weight with time determined when the cup is exposed to a lower or higher relative humidity than that set up within the cup. This simple technique is subject to one serious source of error, especially for relatively permeable membranesnamely, vapor is not supplied t o the lower surface of the membrane as rapidly as it can pass through the membrane, and moisture is not removed from the upper surface of the membrane as rapidly as it passes through the membrane,
FIGURE 1. INTERNAL STIRRERFOR A CUP-TYPE MOISTURETRANSFVSION APPARATUS
Part of the relative humidity gradient thus occurs through the air on each side of the membrane. This situation can be readily corrected on the outer surface of the membrane, when humidity rooms or chambers are used, by blowing air across the surface with a n electric fan, or rapidly passing air over the surface from a humidification train. The device shown in Figure 1 was designed to correct this same difficulty within the cup. It does not interfere with making a vapor-tight seal of the membrane. It permits easy removal of the cups for weighing and does not increase the weight of the cups sufficiently to decrease the accuracy of weighing. It consists of four horizontally mounted pulleys. Pulleys 1, 2, and 3 serve as the supports for three moisture-transfusion cu s, in this case glass crystallizing dishes, which are slightly smafer in diameter than the pulleys. The cups may be clipped to the pulleys so as to be readily removable. The three pulleys are rotated by a continuous belt, B, by pulley 4. Rings made by bending 18-gage sheet-iron strips 1 cm. wide into circular cylinders 3 cm. in diameter were completely covered with tinfoil on the circular surfaces as well as on the ends to make sealed drums, F. Small tinfoil vanes, V , were sealed horizontally on the top face of the drums. These drums, which served as the stirrers, weighed only 5 grams each. They were floated on the liquid in the crystallizing dishes, after which the membranes were sealed to the top. Three electromagnet coils, M , taken from old electric doorbells, were mounted so that the magnet surface just cleared the side of the crystallizing dish. These electromagnets were operated from the secondary of an ordinary doorbell transformer (18 volts). When the pulleys were operated at a speed of about 60 revolutions per minute, the drums, F, were held in a position near the electromagnets as the pulleys and crystallizing dishes rotated. Because of the friction of the drum stirrers on the side of the crystallizing dishes, they rotate about their own axes. The vane, V , on the drum thus rotates with respect to the base on which the apparatus is mounted and also with respect to the crystallizing dish, causing an efficient stirring of the air. The rotation of the crystallizin dish with respect to the stirring drum, F, also adequately caused a continual formation of a new liquid surface. The apparatus was set u p in various relative humidity rooms for making the measurements. An electric fan was directed across the membrane faces. Good check values were obtained when similar membranes were used on each of the crystallizing dishes with a liquid giving the same relative humidity inside each. When the stirring drum was left out of one of the crystallizing dishes, the rate of loss of moisture from that dish was materially less than from the other dishes. When four thicknesses of noncoated Cellophane No. 600 were used for the membrane and the relative humidity gradient was from 100 to 80 per cent, the presence of the stirrer increased the rate of moisture loss by about 70 per cent. Further increase of the rate of stirring had a negligible effect upon the rate of loss of moisture.
