EUeetroUytie generation of
FLUORINE W. C. Schumb, R. C. Young, and IIASSACHUSETTS I S S T I T U T E O F TECHYOLOGY, CAMBRIDGE, MASS.
IN T H E generation of fluorine by electrolSsis of a fused salt bath such as KF.2 HF a t 100' C. with carbon anodes, control of hjdrogen fluoride content v+ ithiii narrow limits is important if polarizatiou troubles are to lie a\oided. A specific gravity method of control w a5 devised, cniplo! ing a narrow >Ionel float of special design, adjustable b? addition of small weights to a stjlusattached to the float. By this means t h e composition of t h e electroly te at the prevailing- cell temperature ma? be rleterniiued qiiic-hl?. The specific gravities of electrol? te mixtures ranging in composition from KF.1.56 HF to KF.1.90 HF, a t 85" to 100" C., were determined by a copper pjcnometer. Measurements of the specific conductivity of fused electrolyte mixtures were made in a speciall) de-
signed cell constructed of Saran, a t 90" t o 100" C. over the range 35 to 1570 hjdrogeii fluoride. The importance of providing for circulation of electrolyte around the cathode during electrolysis was demonstrated by comparative experiments w i t h two cells, in one of which such circulation was permitted and in the other, prevented. iddition of *mall quantities of lithium fluoride to the usual electrolyte was found to be advantageous in lowering the freezing point of t h e bath and t h u s permitting electrol)*is a t lower temperatures with lower hydrogen fluoride content; thi* addition reduces the danger of t h e incidence of polarization but is attended with some uncertainty because of t h e rather small concentration of lithium fluoride which remains permanentlj dissol\ ed in t h e electrol? te.
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T
the capacities of the containers ranging from about 10 to H E experience of various investigators and our own ohper600 pounds of electrolyte. vations indicate that the medium-temperature (about Figure l b shows a typical medium-sized laboratory cell em100' C.) fluorine cell, constructed of steel with carbon as the anode ployed in these studies. The electrolyte charge was about 55 material and with KF.1.8-2.0 H F as the electrolyte, is the most pounds of KF.1.8 HF. The anode was a 3-inch cylindrical nonfavorable combination for the generation of fluorine. The emgraphitized carbon rod supported by a 1/2-inch solid copper rod ployment of nickel anodes in cells operating at room temperature scren-ed tightly into the top of the carbon. A 1.5-inch pipe u p to 100' C. has the advantage of eliminating polarization diffinipple, located centrally in t'he cell cover and iilled with a plug of culties, t o which carbon anodes are a t times subject; but the polytetrafluoroethylene mixed iTith calcium fluoride or of Portdisadvantages of the nickel-anode cell-including the consumpland cement, acted as an insulator for the copper lead and m a tion of nickel, the accompanying formation of considerable support for the anode. The container was made of 8-inch steel sludge, and the rather low current efficiencies obtainable, parpipe, 20 inches tall, integrally welded to a steam jacket made of ticularly at lower temperatures-indicated the desirability of es12-inch pipe. The cell cover, made of '/(-inch boiler plate, wm tablishing the best possible conditions for the proper operation clanipeu to the cell container by means of steel C-clamps, with a of the carbon-anode medium temperature cell. (This opinion heavy asbestos composition gasket (so-called Navy compressed regarding the medium temperature cell is expressed despit'e the s h e e t ) between fact that fluorine the cover and the has been genercontainer. The ated a t tempera25 25 cathode consisted tures ranging from of a thin steel to about -80' I cylinder sus250" C. or higher 20 pended from in20 and from electrosulators in the cell lytes ranging in cover and situated composition from between the dia15 KF.12 or 13 H F 215 phragm skirt and I I to KF.HF, with 0 0 11 the cell wall. No various types of z I A diaphragm screen e l e c t r o d e s and IO IO was employed materials of cell because of the construction .) close streamlining I n some pre5 5of the f l u o r i n e liminary experiliberated a t the ments a number anode, which preof cells were conQ Q vented mixing of structed, some of a the gas with hys t e e l , s o m e of drogen from the copper, others of Figure 1. Small Fluorine Cells, (a)w-ith Cell Wall as Cathode, and (b) with cathode: and the copper-lined steel, Cathode Insulated from Cell Wall
tl"
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244
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1947 12
IO
8 Lo
c
2
0
Figure 2.
Voltage-Amperage Characteristics of Small
Fluorine Cell A. B.
Over-all cell voltage Anode t o electrolyte
C. L).
Anode probe to cathode probe Electrolyte to cathode
spacing of the cnthode and diaphragm TWS sufficiently n.ide t o prevent mixing of much hydrogen rvith the anode ga-. The operation i i i this cell vas at 7.5 t o 8.0 volt., with a n aiiode current density of 60 to 100 amperes per sr1u:ire foot. I n the c o u r v oi rome preliminarj experiments (rarried out in 19-12-43 by E. L. C;anible, -1.J. Stevens, H. II. .hder>on, and H. E. Ramsden), the voltage-amperage characteristics of a snxrll, open, lnborator?--~izecell xere studied hy placing tn.0 auxiliary or prohe carbon electrodes close to t h e anode and cathode, i ~ e spectively: the cell electrodes Ivere Iinrdlel plates of carbon and qteel, each of 0.073 aquare foot in effective area and placed ci inches apart in IiF.1.8 HF electrolyte a t 110" C. The voltage drops from anode to electrolyte, from electrolyte t o cathode, a i d m a d e prohe to cathode prohe, as !\-ell as the over-all cell voltage, are s1ion.n a-: a fuiiction of the amperage (or current density) iii Figure 2 . The vo1t:ige drop from anode t o electrolyte is seen t o he distiiictly greater than that from electrolyte to cathode. and the contribution due to the resi5taiice of tlie electrolyte (curve C ) groivs liiiearly a < the current density increa5es. In a n attempt to diminidi the tendency of carboii anode. til polarize, the expedient of superimposing alternating current on tlie tlircct elrctrolyziiig current wai tried: alternating current tlen-ities up to 100 nniperes per squaw foot, n-ere imposed on direct current denFities up to 330 amperes per square foot, t h e potenti:?l drops from anode to cell and cathode to cell heiiig measured. The cnthotle-to-crll voltage iva.5 unaffected, and, although lome effect ab observed in the reduction of anode-to-cell potentinl. especially at lon-er direct current densities, the over-all resulti were not sufficiently promising t o recommend the adoption cli this procedure in general practice. DETER\IIS.ATION O F ELECTROLlTE CO\IPOSITIOS
-1flo:it device WIG con~tructedof LIonel tubing lveighted at the bottom by a section of solid None1 rod: at the upper end it bore :L derider forlied et).lus to which sniall perforated weights could he attnched to bring the float t o a predetermined equilibrium position. Two sets of these auxiliary weights v e r e required. The pieces of one of the sets Tvere made of such sizes that, ~vhen the temperature of the electrolyte \vas laon-n, the addition of the proper n-eight from the set n-odd adjust the float for the prevailing temperature; then a second weight, selected by trial from the second set and attached to the stylus fork, brought the float to tlie reference position. The percentage stamped upon this second iveiglit indicated directly the hydrogen fluoride coiltent of the h t h . The entire operation could he carried out nithill
2 45
two minutes. The indicated hydrogen fluoride content n'as ,iho\vn t o be sufficiently accurate for the purpose intended by comparing the results obtained by the specific gravity method of electrolyte samples taken a t n i t h those furnished by anal) the same time. The calibration of the float \vas carried out by immersing it in electrolyte samples of known composition contained in a cylindrical 3Ionel pot, about 1 liter in capacity, immersed in a steamjacketed pot containing the electrolyte. The specific gravities of huch mixtures viere determined by means of pycnometers of about SO-1111. capacity constructed entirely of copper (Figure 3). T n o flat-bottomed copper dishes Jvere vieldrd together rim t o rim and formed a closed box. Holes were chilled in the top and bottom edges of the box, diagonally, and narrow copper illlet and outlet tuhes irere ~i-eldedinto these holes. \\'hen the xeighed pycnometer iva- filled by immer on in the l l o n r l container and wllon-ed to come to thermal equ ibrium n i t h tlie coiit:liiier niid contents, it ivas removed and, after cooliiig, clenned extermlly and weiglied. Calibration of the pycnc~nicterW:I> c n r r i d out hy the usual method of weighing xheii fillcd xvith xl-atrr :\t n lmoivn temperature, the volume at, the drsired higher temlwrature being calculated !?it11 the aid of the linol\.n cuhicnl eoefficient of expansion of copper. The specific yr:ix-itirs of electrolyte mixtures determined in this x a y at 85' to 100' C. are 211o1vn in Figure 4 and Tables I and 11. I n the grapli t i l e numhers under the e-Cperimental points e the ratio.: C J f the mole; of h)-dl,open fluoride to moles of pot ium fluoride iii the pnrticulnr w n p l e s taken. Tnble I shov--i:some of the experin1ent:il data upon 11-hich the graph as n vhole K:IS based.
Figure 3.
Copper
Pycnonieter
Table I1 a h o w the d a t a a t rounded concentlaticins of hydrogen fluoride and a t rounded temperatures of 90", 95', and 100" C. In the graph the parallel lines represent the specific gravities of electrolyte of t h e compositions indicated, ranging from KF.1.76 HF t o KF.1.90 H F a t 85 to 100' C. SPECIFIC CONDUCTIWTY O F ELECTROLYTE J I l X T U R E S
-1knonledge of the electrical conductivity of t h e electrolyte w e d in the fluorine cell would be desirable, not only to shed light on the general characteristics of the cell b u t also to allow devising a niechanism for continuously evaluating the hydrogen fluoride
T . ~ B LI.E SPECIFIC GR.IT.ITI-O F ELECTROLYTI: Moles HF. 3Iole IiP
Temp.,
1.761 1.769 1 76s
86.0 91.0 92,s 100 7 91.0
O
C.
Sn.Gr. 1 937 1 930 1 928 1 920 1.023
AInles Ilole
ET/ kF
1,882 1.83 1 86: 1 Si, 1.882
Teriip., O
C.
86.5 93 2 99.0 85 0 Y:1 5
$12,
Gr
1.926 1 917 1 906 1 020 1 006
INDUSTRIAL AND ENGINEERING CHEMISTRY
246
1900
1.910 SPECIFIC
1.920 GRAVITY
1.930
Figure 1. Specific Gravity of Electrolyte
content of t h e electrolyte according t o its conductivity. For this< purpose i t was necessary t o devise and construct a suitable cell in which the specific conductivity of KF-HE' mixtures couid he measured accurately a t about, 100' C. Preliminary tests indicated t h a t hard rubber or Saran n-ould he possible materials of const,ruction for the cell body, and of these Saran proved somewhat better a' regards danger of plastic deformation at higher temperatures. I t is probable that still furtlier improvement in this regard may be possible n i t h other phstic materials, \\-liicli n-ere not available a t the time. Figure 5 s h o w the construction of the cell. T h e sections of tlie cell n-ere made of solid Saran st,ocl;, drilled out to form a tem of tubes and joined together by fine thre:ids cut into tlie endof the sections. T h e horizontal section of the cell had a l,'a-incli hole drilled through it, n-idened a t t h e ends adjacent to the electrodes; the latt,er were 1-inch circular platinum disks held i i i position by the Saran caps threaded t o the ends of tlie tube. Thc three capped T-tubes were screwed into the horizontal tube, one at, the center for filling and one at each end for vents. The disk electrodes \yere welded on the back faces to platinum wires, n-hich passed out through fine openings in the Saran caps and \\-ere cemerited closed with a drop of molten Saran \J-lien tlie cell w:is ready to be immersed in the thermostat, for nieasurenient. The mixtures of KHF, and HF, of vhich t.lie conductivities were to be measured, n-ere made up in closed copper container. with capped inlet and outlet tubes, from which t h e cell could I)? filled and a sample taken for analgsis a t the same time in thimblesized platinum crucibles. The electrical apparatus consisted of 3 conr-e~itionalpotentiometer hookup, with a Leeds 8- S o r t h r u p Type 7631 poteiitiometer and volt box and a General Radio audio-oscilliitor operating a t 1000 cycles per second, used in conjunction with a telephone receiver. T h e thermostat, which viis well lagged, was filled with Minernl S e d oil and \vas regulated in tlie usual
Vol. 39, No. 3
manner with a mercury regulator. Over the range 90" to 100" the control of temperature was good to = t O . O j n C. T h e cell constants were determined using potassium chloride solutions made up t o be 0.1 N a t the particular temperature being investigated. T h e specific conductances of t,hese solutions were taken from International Critical Tables (Volume VI, page 234) : a t 90" C., 0.03071 ohm-'; at 95", 0.03213; a t loo", 0.03356. The cell constant of the Saran cell used in the final measurements was 93.5, approximately constant over t h e range 90" to 100" C. The procedure employed in carrying out t h e conductivity measurements consisted of filIing t h e cell with hot electrolyte rnirture previously prepared in the copper containers. The filler :ind vent tubes were then closed with screw caps, and the cell wi~ pl:iced in the thermostat a t the desired temperature. X h e n tlierninl equilibrium had been attained, readings were made with the potentiometer; a number of settings were used on the volt hox, and a nuniber of readings were taken for each setting. The re11 was then emptied, disassembled, and cleaned by washing and brushing with warm soapy n-ater, rinsing with distilled watw and alcohol, and drying in vacuo. The platinum di-k electrode:: were also removed, scoured xvith a gentle abrasive, wished, and dried a t 110" C. The cell was then reassembled fil!ed n.itli electrolyte of the same composition as t,hat previously used, and replaced in the b a t h ; when thermal equilibrium was reached, the conductance was again measured. By t,his proccdure reproducible values were obtained, whereas if the cell was simply emptied and refilled a t once, check readings were not obtained. (In some of the preliminary conductivity work difficult,y had been encountered in t h a t a gradual drift in the values obtained on successive fillings with electrolyte was noted, which was not experiencrd when aqueous potassium chloride ivas used in the determination of the cell constant. However, the complete disassembling of the cell each t,ime a filling \vas made, together with scouring of the platinum electrodes and reassembling and ' drying the cell, proved adequate in providing consistent re'cid ings. The cause of the drift referred to is not clear, h u t the authors believe that a film is produced on the surface of the platinumconceivably a coating of fluoride-Jvhich may affect the conductivity readings and t h a t the removal of this film reltores the original values.)
T.4BLE
11. SPECIFIC GRAVITYO F A S D 100"
% HF
Moles H F / Mole KF
44.7 44.5 44.1 43 2 41.9 41 1 40.7 .? 9 4 39 0 37 6 37.4
900
ELECTROLYTE AT
c.
go", 93",
Specific G r a v i t y a t : 950 1000
c.
c.
0.245 0.232 0 226 0.195 0.175 0.163
0 260 0.253 0.243 0.205 0 19'
0 ' i35 0.131 0.110
0.147
0.180 0.167
0.151 0.128 0.122
c.
0.2i7 0.2i3 0,286 0.224 0.210 0.156 0.184 0 165 0 164 0.143 0.143
The conipositioii of the elect,rolyte yLuied from 37 to ASc.( hydrogen fluoride, and the tempernture range \yas 90" t o 100" C. Table 111 is a summary of these data, which are believed t o he fully as accurate as the analytical determination of the hydrogen fluoride content of the electrolyte. Figure 6 sliowa thesr results graphically.
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1947
EFFECT O F E L E C T K O L I T E CIRCULATION ABOUT CATHODE
247
peres (100 amperes per square foot) Tvithout trouble, h u t not more than 30 amperes (75 amperes per sqi1:ir.e foot) could be mrried if the longest cathode (16 inches) v a s used: otherwise, polarization set in. The temperature of the cell n - a s observed to rise more quickly and to undesirably high limitr rvhen vertical circulation about the cathode v-a,5prevented. Ue>t performanet. of the cell with all combinations, a t current densities of 65 nmperes per square foot or over, \vas observed at, 98" * 2 ' C. .\t 103" C. or over, serious voltage rise, resulting iii complete polarization, set in rapidly. The benefit of circulation about the cathode n-as also noted in the following niaiiner: If the cell \vas oper:iting a t 95 ', for example, without esternal heating, and if the steam was then turned on, :in immedi:ite drop in voltage--particulnrly skirtto-cathode voltage-would occur; thi? drop was greater than could be accounted for merelv by the increase in t.emperature of the electrolyte. It appears probable that turning on t h e steam resulted in improved circulation about the cathode. These results indicate that provision for circulation about t,he cathode is desirable in plant cells for p o m o t i n g ti ouhle-free operation and especially lon-er cathode rotentials.
In order t o teat t h e importance of providing for circulation of electrolyte about the steel cathode in the design of fluorine cells, the performance of two cells )vas studied; in one such circulation \vas permitted, whereas in the other circulation \vas prevented. Figure 1 ih01vs t,lie arrangement of the tn.0 cylindrical cells. Figure In is a smaller cell of about 50-pound capacity of electrolyte ( K F . l . 8 5 H F ) i n which the cell wall acted as the cathode.
CATHODE POLARIZATIOK AND BIPOLARITY O F CELL DIAPHRAGII
Figure 5.
Conductivity Cell
The larger cell of 75-pound electrolyte capacity had a cylindrical, inwlated steel cnthode of the same inside diameter :is the cell wall in the ?mnller cell; this cathode was suspended from the cell cover. The latter arrangement permitted circulation of electrolyte around, over, and behind the cathode in a manner which \vas not possible in the smaller cell. Several &tee1cathodes x e r e constructed 8, 12, and 16 inches in length, respectively. T h e 16-inch cathode was tall enough to extend above the surface of the electrolyte and t o prevent any circulation over the top of the cathode, xhereas the shorter cathodes were completely immersed in the bath. t T h e results obtained in comparative tests with these tivo cells indicated that circulation about the cathode was beneficial, in t h a t cooler operation of the cell was maintained, and thereby the use of larger current densities was permitted ivithout resultant polarization difficulties. Thus it was found that, n-ith the 8- and 12-inch cathodes, which permitted vertical circulation of electrolyte ahout, t h e cathode, the cell could be operated at 40 am-
37
I
I
38
39
I
40
PERCENT
Figure 6.
In the course of the experiments described, frequent measurements were made of anode-to-diaphragm skirt arid skirt-tocathode potential drops. It was concluded that cathode polarization appeared concurrently with the development of bipolarity of metal parts interposed between cathode :ind anode, especially the solid diaphragm skirt. The follon-ing data are representative of the behavior of the cell as polari;.ation developed: The 16inch cat,hode ]vas supended in such a ~ v a yas to emerge above the level of the electrolyte and thus prevented vertical circulation of electrolyte around the cathode. 33 miperes (81.7 amperes per square foot) the cell rapidly polarized; the current fell and the voltage rose until, a t a n over-all voltage of 25 volts, explosion occurred Tvithin the cell. These results ivere ob3erved repeatedly. I n a period of several minutes the following mcarurements were recorded: Skirt-to-Cathode Voltage
1 8 14 0 15.0 16.5 17.0 4
.%node-to-Skirt Yoltage 6.0 7.0 7 6 8 0 8.2a
.kinperage 33.0 27.5 15: 1
..
Wayers followed b y explosion
I n the operation of plant-size cells it n - : ~ observed t h a t serious corrosion of the diaphragm skirt on the cathode side may be encountered because of the establishment of bipolarity of the skirt.
I
I
41 42 H F IN E L E C T R O L Y T E
43
Specific ConductiTity of Electrolyte
44
45
248
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 39, No. 3
If the skirt is perforat'ed t o permit :I greater degree of electrolytic -Itroublesome feature attending the eniployment of lithium conductivity, the corrosion may be r( duced t o a considerable defluoride (or aluminum fluoride) in the eltctrolyte is the fact t h a t gree. As long as the interposed diaphragm offers any material the concentration of the added fluoride appears to diminish proamount of solid area t o "shadow" the cathode, the incidence of gressively n-ith time, until finally it reaches such a small value t h a t its beneficial effects disappear. ;ipparently the lithium bipolarity of t h e diaphragm is to be expected; and the greater the current which is passed through the cell under these circumfluoride is carried down into the sludge a t the bottom of the cell, for it vas observed t h a t , if the sludge is stirred u p after disapstances, the more serious this effect. At low current densities the bipolar skirt acts normally; iron pearance of the lithium fluoride from the elect'rolyte, there is is dissolved from t h e anodic area facing the cathode while hydrotemporary improvement in the operation of the cell as regards polarization difficulties. Similarly, when aluminum metal was gen is liberated from the cathodic area facing the anode. This hydrogen is consumed quietly-or, a t most, with a slight crackling c:iii>ed to dissolve iri the electrolyte to form aluminum fluoride, sound-by the fluorine in the anode compartment. Hov-ever, the clear, supernatant liquid \vas practically free of dissolved nluniiiium after standing for some time; this indicated that the when the current density is increased, the anodic areas on the true solubility of aluminum fluoride in this medium must be surface of the diaphragm tend to become passive, with a consequent rise in the skirt-to-cathode potential. The cathodic face quite .m:ill :t?id that the colloidd dispersion first formed is Inter deposited as a sludge o n the bottom of the container. of the skirt retains its act'ive condition, and the anode-to-skirt The esact role played by lithium fluoride in preventing the involtage changes b u t little. When the evolution of hydrogen in t h e anode compartment reac1.e~a sufficent rate, ex; l o ~ i ~ e cidence of polarization is not clear: whether the pheiionierion is essentially dependent on the colloidal characteristics of the interaction v i t h fluorine results. solid when dispersed t o allow its contact with the electrodes, or I n practice t h e anodes aiid cathodes are generallj- >ituated so \vliethei the added salt improves the netting characteristics of t h a t only t h e perforated portions of the diaphragm (or screen) are the electrolyte and so obviates polarizat.ion of the carbon anodes interposed between them. This arrangcment teiids t o hinder by ari insulating gas film, are matters of conjecture. (The esirtthe e9tahli;hment of a bipolar condition. ence of such a gas film surrounding the anodes was clearly obThis discussion does not include a consideration of the condiserved iii an uncovered laboratory cell in which electrolysis ~va' tions attending polarization of the carbon anode, a phenomenon pi oceediug with small cylindrical carbon au0de.s. .It sufficiently which has received much attention. T h a t these tivo types of high current densities the escape of the fluorine in n narrow polarization are distinct \vas demonstrated by the following exsheath surrounding the carboii \vas visible, and a multitude of periment: With a 6-inch cathode in place of the longer ones aiid minute sparks could be seen traversing the gas envelope hetxveen with the top of the submerged carbon situated an inch belon. the carbon and the surrounding liquid.) Spectroscopic deterthe diaphragm skirt, so t h a t practically no "shadon." was mination of t,he lithium contained as lithium fluoi,itle in the thrown on the cathode, i t was found that cathodic polarization electrolyte was secured on three samples (supplied hy the rewas entirely eliminated u p t o 50 amperes (128 amperes per square search laboratory of The Hnrshan. Chemical Company). One foot). .It this point anodic polarization made its appearance; !vas freshly prepared, t,he second had been in use for a short peanode-to-skirt voltage rose several volts in a feiv minutes, riod in a plant-size carbon-anode cell, aiid the third sample had whereas the skirt-to-cathode drop rose only 0.3 volt. It should been run for a long period in a lnbomtory-size cell. The results be noted, however, that a t the practical operating current of these nnalyses showed clearly that, with continued use, the type of densities-60 t o 70 amperes per square foot-this lithium fluoride content of the electrolyte n-ne progressively reanodic polarization should be a rare occurrence, especially duced to a small fraction of t h a t originally pre-ent. Of an origiif lithium fluoride has been added to the electrolvte. l i d l,Src lithium fluoride incorporated in the electrolyte. less than 0.2", n a s f o m d in the thin3 naniple. ADDITION OF LITMIU\I FLUORIDE OR .kLU\IISU\I FLUORIDE T O ELECTROLYTE
K i t h the idea of reducing the proportion of hydrofluoric acid in the electrolyte and so diminishing the losses by vaporization from the bath, a number of experiments were carried out with the addition of a second metal fluoride to the mixture of KHF2 and HF. Of the alkali fluorides other than t h a t of potassium, most success was obtained Jvith lithium fluoride, which is slightly soluble in the conventional electrolyte a t 100" C. The exact solubility has not yet been ascertained with certainty, b u t it is probable t h a t not much over 1% of lithium fluoride is truly dissolved, and possibly even less than this quantity. T h e effect of this small percentage of lithium fluoride is noticed, however, in a lowering of the freezing point, so t h a t the electrolyte may be employed a t temperatures well below 100" C. iyithout solidificntion. .%lternatively, the addition of lithium fluoride permit. reducing the percentage of hydrogen fluoride in the bath at 100' C., with resulting advantages in the operation of the cell, especially in greater freedom from anodic polarization problems.
ACKYOR LEDGJIEhT
tance of the 1Iadi.mi Square .%rea, Vnited States Rice, under whose auspices this investigation way carried out, as n-ell as that, of the Sational Defense Recearch Conmiittee in some of the earlier work, is gratefully acknon-Iedged. Considerable informative aid Tvas also received from other poiips interested in fluorine re?earch, .such as the Hooker Electrochemical Company, Du Pont de Semonrs 8r Company. Iiic., The Harshax Chemical Company, and Iiellex Corporation, and from Robert D. Folvler of The Johns Hopkins University. before the Symposium o n Flrrorine Chemistry a s g a p e r Dij-ision of Industrial and Engineering Chemistry, 110th Alecting oi .I>IEP.IC.LS CHEIIIC.LLSOCIETY. Chicago, Ill. T h e work described i n !,.?per is covered also i n a comprehensive reuort of work with fluorine tl1:orinated conipounds undertaken i n connection with t h e P i o j e r t . Tliis report is soon t o be published as Yolume I of Div the 1 I a n l i : i r t a n Project Technical Series. I'nEiEsTED
30. thc thi.
and
