T H E J O U R N A L OF 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
646
Vol.
12,
No. 7
considerable attention t o t h e production of soluble phosphates b y means other t h a n the usual method of treating phosphate rock with sulfuric acid. Perhaps t h e most attractive and in many ways t h e most promising of these processes is t h a t in which an intimate mixture of a natural phosphate, silica, and coke is smeltered a t a high temperature, with t h e result t h a t silicates of lime are formed and t h e phosphoric acid volatilized and subsequently collected in some suitable manner. This process is really based on t h e method long in use for the rnanufacture of phosphorus, and in order t o separate completely the phosphoric acid from t h e lime i t is apparently necessary t o have a sufficient quantity of reducing agent present t o produce elementary phosphorus according t o t h e equation Ca3(P0& 3Si02 jC = 3CaSi08 zP 5CO. The phosphorus produced is subsequently burned or oxidized within or outside of t h e furnace b y carbon dioxide or air thus 2PZ so2 = 2Pz06 or P2 5co2 = Pzo6 f 5co It has been generally believed t h a t the temperature and other conditions necessary t o volatilize completely phosphorus and phosphoric acid from natural phosphates could be attained only in the electric furnace,’ and t h e Bureau’s early experiments were therefore conFIG. 11-EFFECT OF AIR ON “I,” FOR STEAM: X = P E R CENT STEAMBY ducted in furnaces of t h e arc type. As the results of VOLUME,h =FILMCOEFFICIENT these investigations have been described in previous Inspection of the curve on Fig. I indicates t h a t articles, only a brief outline of t h e work is given in the i t has the form indicated by t h e exponential equation present paper. h = a&*’, The first experiments were carried on in a rather where a and ,8 are constants t o be determined and crude electric furnace constructed a t t h e Bureau’s x is per cent steam b y volume. I n order t o test t h e experimental laboratories a t Arlington Farm, Va., a n d applicability of this type of equation, i t may be recti- here t h e Cottrell method of electrical precipitation fied as follows. Take t h e logarithm of both sides of was first successfully applied t o t h e collection of t h e volatilized phosphoric acid. Ross, Carothers and t h e equation Mer22 showed t h a t by this means there could be oblog,h = log,a Px. If a plot of t h e d a t a in t h e form of (log& - log,a) tained an acid of such high concentration t h a t t h e versus “ x ” indicates a straight line, t h e equation added cost of manufacturing phosphoric acid by theselected is satisfactory. Since when x = o, h = a, volatilization process would be partly offset by t h e saving in transportation charges in shipping and * . a = IO, and t h e resulting plot is shown on Fig. 11. The proper value for /3 was found by averaging all distributing t h e product. Later a larger and more of t h e points, t h e resulting equation having t h e form complete furnace with auxiliary apparatus was constructed at Hoboken, N. J. log,h = 2.303 0.0566~ I n reporting on this work Carothers3 showed t h a t , or h = 2.303 e 0.0566~ assuming the price of electric power a t $ 2 5 per h.-p. a more convenient form of the equation is yr., phosphoric acid ( P 2 0 6 ) could be produced and recovered at a cost of 3.37 cents per pound exclusive logloh = I 6.0240%. A plot of this equation is represented by the curve on of interest on investment, taxes, and royalties. By using t h e acid t h u s obtained t o treat more phosphate Fig. I. rock, however, a double superphosphate could be THE PRODUCTION OF PHOSPHORIC ACID BY SMELT- produced which brought down t h e price of t h e unit ING PHOSPHATE ROCK IN A FUEL-FED FURNACE of soluble phosphoric acid very appreciably. The By William H.Waggaman and Thomas B. Turley figures indicated t h a t under t h e abnormal conditions BUREAU OR Sorbs, U. S DEPARTMENT OF AGRICULTURE, WASHINGTON, existing a t t h a t time, t h e cost per unit of phosphoric D, C. acid produced by t h e volatilization process compared [PRELIMINARY REPORT] favorably with t h e cost of this ingredient in ordinary Received March 1, 1920 superphosphate obtained b y t h e sulfuric acid method.. Ever since t h e early days of t h e war when t h e high I F. S. Washburn, U. S. Patents 1,044,957 (1912); 1,100,639 (1914). cost and scarcity of acid phosphate seemed t o menace t TEISJOURNAL, 9 (1917), 26. our agricultural interests, t h e Bureau of Soils has given 8 Ibid., 10 (1918), 35. 1 I I = _. h, + + 4.45(510)0’8 h, = 2 5 0 0 Table I gives t h e results of the calculation for all of t h e tests. Fig. I shows values of percentage of steam plotted against film coefficient-h,. T h e data include steam percentages down t o 66 per cent only. The film coefficient for zero per cent, t h a t is, all air, has been the subject of much careful work, t h e values of h being a function of the velocity and varying between I and 20. Since no information was given in Professor Kerr’s experiments as t o t h e rate of removal of t h e air, t h e writer selected a mean value of I O for this point in order t h a t it might be possible t o derive a suitable empirical equation t o fit t h e above calculation. I
510
+
+
+ +
+
.
+
+
+
+
July,
1920
T H E J O U R N A L OF 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
647
TABLE I-VOLATILIZATIONOF PHOSPHORIC ACIDFROM MIXTURESOF TRICALCIUM PHOSPHATE, SILICA,COKEAND ALUMINA B Y SXELTING IN OPEX AND CLOSEDCRUCIBLESIN A DENTAI. FURNACE BY MEANSOF ILLUMINATING GAS AND AN AIR BLAST Length PzOq PROPORTIONS O F MATERIALS of PnOs in Volati-USED IN CRARGETemperature Time Slag lized Sample Caa(PO4)n Si02 AIzOP Coke -PERCENTAGECOMPOSITIONAtJained Heated Per Per cent Character No. Crucible Grams Grams Grams Grams Si02 CaO AlnOa P2Os C C. Hrs. cent of Total of Slag 12A Closed (Clay) 20.0 16.6 5.2 40.7 25.9 0 . 7 21.9 10.8 Above 1400 0.75 3.24 8 9 . 8 Fluid, grayish black 12 G . . Open (Clay) 20.0 16.6 5.2 40.7 25.9 0 . 7 21.9 10.8 Above 1400 1 7.20 76.2 Viscous gray. White bloom on surface’ 12N1 Open(Graphite)20.0 16.6 6.6 5.2 35.1 22.4 14.3 18.9 9.3 1200 1 4.92 8 0 . 4 Viscous black Open (Graphite) 20.0 16.6 6.6 5.2 35.1 22.4 14.3 ‘18.9 9 . 3 Above1400 2 None 100..0 Fluid black 12Nz 12 0 Open (Clay) 20.0 16.6 . 4 . 8 41.1 26.2 0 . 7 22.1 9 . 9 Above 1400 1 3.36 89.3 Fluid’light gray 12 P Open (Clay) 20.0 16.6 6.6 5.0 40.9 26.1 0 . 7 2 2 . 0 10.3 Above 1400 1 2.22 93.0 Fluid’, light gray; bloom on surface’ Open (Clay) 20.0 16.6 6.6 5.4 40.7 25.8 0.7 21.8 11.0 Above 1400 0.75 4.65 84.9 Fluid light 12 Q blobm on 12 R.. Open (Clay) 20.0 16.6 6.6 5.6 40.5 25.7 0 . 7 21.7 11.4 Above 1400 0.75 2.45 92.2 Fluid, light gray: bloom on surface’ 121 Open (Clay) 20.0 16.6 6.6 5.2 40.7 25.9 0.7 21.9 10.4 1300 1 Trace 100.0 Fluid, light gray; large bloom’ 122 Closed (Clay) 20.0 16.6 6.6 5.2 40.7 25.9 0 . 7 21.9 10.4 1300 1 Trace 100.0 Fluid, all slag 1211 Open (Clay) 20.0 16.6 2.0 5.6 38.7 24.5 5.2 20.7 10.9 1300 1 5.28 81.3 Viscous light gray; bloom on surface1 1212 Closed (Clay) 20.0 16.6 2.0 5.6 38.7 24.5 5.2 20.7 10.9 1300 1 1.91 93.6 Viscous dark; no bloom 1216 Open (Clay) 20.0 20.0 2.0 4.8 43.6 23.2 4 . 9 19.6 8.7 1300 1 4.26 83.7 Viscous gray; large bloom’ 1218 Closed (Clay) 20.0 20.0 2.0 4.8 43.6 23.2 4.9 19.6 8.7 1300 1 3.52 86.6 Viscous gray: no bloom 1217 Open (Clay) 20.0 22.0 2.0 4.8 45.9 22.2 4 . 7 18.8 8.4 1300 1 3.90 84.3 Viscous gray; large bloom1 121s Closed (Clay) 20.0 22.0 2.0 4.8 45.9 22.2 4 . 7 18.8 8.4 1300 1 3.75 8 4 . 8 Viscous gray; no bloom 1 An analysis of the bloom or white crust on t h e surface of slags obtained in open crucibles shows a considerably higher percentage of phosphoric acid than in the original mixture. The proportion of lime t o phosphoric acid coincided very closely with t h a t in calcium pyrophosphate (CazPz07).
.... ..
..... .. .... .... ..... .....
0
..
.....
surfs%';
.. .... .. ...... ...... ...... ......
...... ..... ... ..
I n a later investigation, Waggaman and Wagner’ pointed out t h a t by using the “mine-run” phosphates of Florida, which in their natural s t a t e contain impurities which preclude their treatment with sulfuric acid until they have been p u t through an elaborate washing and screening process, a great saving in phosphate could be effected and the cost of t h e soluble phosphoric acid produced therefrom very materially reduced. The high cost of electric power in this country, however, made i t appear very desirable t o test out t h e commercial possibilities of producing phosphoric acid for fertilizer purposes in a fuel-fed furnace, and, since crude oil is t h e cheapest and most accessible fuel for t h e phosphate regions of Florida, i t was decided t o undertake experiments with a view t o producing phosphoric acid by this means. LABORATORY E X P E R I M E N T S
Preliminary work i n t h e laboratory, where various mixtures were heated in a dental furnace by means of gas and an air blast, showed t h a t contrary t o general opinion t h e nearly complete evolution of phosphoric acid from a charge of calcium phosphate, carbon and quartz flour was perfectly feasible provided t h a t reducing conditions were maintained until a fusible slag was produced, and a temperature of approximately 1500’ C . was continued throughout t h e operation. Table I shows in part t h e results obtained by heating such mixtures, with and without the addition of small amounts of aluminum oxide, in both open and closed fire-clay crucibles. An inspection of Table I will show t h a t as a rule considerably better results were obtained where the crucibles were kept covered so t h a t the oxidizing gases were not allowed t o come into contact with the charge. When the crucibles were left open, i t was noticed t h a t a white crust or “bloom” almost invariably formed over t h e slag and no matter how long t h e high temperature was maintained this crust gave no sign of melting. The quantity of this crust in a number of 1
THISJOURNAL,10 (1918), 353.
instances was equal t o t h a t of t h e underlying slag. I t is assumed t h a t the phosphoric acid distilling from the lower part of t h e mass recombined with or was fixed by the lime a t the surface where oxidizing conditions prevailed, forming calcium pyrophosphate according t o t h e following equation: zCa3(PO&
+ PzO~
= 3CazP207
It was found, however, t h a t when t h e fusion of t h e charge was well under way and the carbon or coke thus protected in the mass of molten slag, the covers of t h e crucibles could be removed without t h e formation of this crust and t h a t t h e reaction continued in spite of the oxidizing conditions a t t h e surface of the slag. The addition of small amounts of alumina t o the charge seemed t o aid t h e fusion somewhat, it being a wellknown fact t h a t t h e presence of this substance i n limited amounts lowers the melting point of both acid and basic slags. I n most of these mixtures t h e ratio of silica t o lime was approximately 39 t o 61 per cent, but i t was found later, in dealing with the natural phosphates of Florida, t h a t better results could be obtained by varying these proportions according t o the composition of the mineral used. These laboratory experiments pointed almost conclusively to t h e necessity of maintaining reducing conditions in t h e phosphatic charge until fusion has begun, and i t appeared a t first sight t h a t t h e most practical method of doing so in a mass containing much finely divided material, such as t h e pebble phosphates a n d the mine-run phosphates of Florida, was t o heat t h e mixture in a separate chamber so t h a t t h e oxidizing gases from the burning fuel would not come into cogtact with t h e charge until the latter had been brought t o a state of incipient fusion. LARGER SCALE E X P E R I M E N T S
Accordingly in order t o test this process on a semicommercial scale, a fire-brick furnace of t h e t y p e shown i n Fig. I , described by t h e senior author and
648
T H E JOURhTAL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
others in U. S. Patent 1,282,994,was constructed a t Arlington Farm, Va. This furnace comprised a central or inner chamber (holding about I 50 lbs. of charge) open both a t t h e top and bottom but constricted somewhat a t its lower end t o prevent the charge from working through too rapidly. This chamber was supported on arches of carborundum brick above a hollow hearth intended t o receive t h e molten silicate. The whole was surrounded by an outer chamber into the opposite walls of which were set two oil burners so placed t h a t their flames played upon and around t h e lower part of t h e inner chamber, heating t h e charge by radiation through t h e 4-in. walls. Any fumes which were evolved from t h e smelting of the mass were t o be drawn down through t h e charge chamber and passed together with the gases of combustion onto t h e Cottrell precipitator in order t o collect t h e phosphoric acid. ~
Vol.
12,
No. 7
into t h e furnace along with the fuel was then tried; one oil burner was entirely cut off and a concave baffle of carborundum brick built opposite t h e other burner. The charge was placed in a hopper from which it was mechanically fed through a screw conveyor and blown into t h e furnace against t h e baffle in a spray under an air pressure of 30 lbs. t o the square inch. It was found t h a t if t h e charge was fed into t h e furnace very slowly a certain amount of slag low in phosphoric acid formed upon and r a n down the wall of t h e baffle, but t h e vast bulk of t h e material, owing t o its finely divided condition, was carried out of the furnace along with t h e gases of combustion and lost. After several trials with material of various degrees of fineness this method was also abandoned. B R I Q U E T T I N G T H E P H O S P H A T E CHARGE
It was then thought t h a t perhaps t h e nodulizing or briquetting of t h e phosphate charge might present a solution of t h e problem, and experiments were begun on t h e briquetting of mixtures of finely ground pebble phosphate, sand and coke, using various binders such as solutions of magnesium chloride, calcium chloride, calcium, sulfate, sodium chloride, sodium silicate, phosphoric acid, and an acid sludge from t h e refining of petroleum. Short cylindrical briquettes I in. thick and I in. in diameter were made in a mold under a pressure of about I ton, b u t none of t h e binders employed proved satisfactory since t h e briquettes (either air dried or oven dried) shattered when dropped upon a stone table from a height of I t o 3 f t . In t h e Florida hard-rock regions, however, the phosphate deposits in their natural state contain much soft phosphate and clay-like material of considerable plasticity, and it was thought t h a t possibly t h e binding qualities of this mine-run phosphate might prove sufficiently effective without t h e addition of any other ingredient. FIG.I-FURNACE USED IN FIRST EXPERIMENTS
This indirect method of heating the charge proved so inefficient and entailed such a loss of heat t h a t after several trials lasting from 18t o 24 hrs. i t was abandoned as impractical, and no molten slag was obtained, although a certain amount of phosphoric acid was driven off, and a sintered product obtained in the charge chamber. The experiments showed quite clearly that in order t o make the process economically practicable t h e full calorific power of t h e fuel must be utilized, which can be done only by heating t h e charge directly in t h e flame. This conclusion only served t o emphasize t h e problem of how t o maintain t h e reducing conditions necessary for t h e volatilization of t h e phosphoric acid, when t h e maximum efficiency of t h e crude oil flame, or t h a t of any other fuel, can only be obtained under oxidizing conditions. Moreover, t h e phosphates with which t h e experiments were being conducted are of such a character t h a t i t is impossible t o handle t h e m in a plant of t h e blast. furnace type, as a flame cannot be forced through a mass of such finely divided mat eri al. At t h e suggestion of Professor Whitney, chief of this Bureau, the plan of spraying the phosphatic chargs
ANALYSISOF FINELY GROUNDFLORIDA PEBBLE PKOSPKATG, MINE-RUNPKOSPHATE, AND FURNACE CHARGES MADEUP PROM T B E S E PHOSPHATES PERCENTAGE OR VARIOUSSIZED PARTICLES IN SAMPLES
TABLE11-MECHANICAL
Phr -
Gravel and Medium Fine Coarse Sand Sand Diam. Sand Diam. Diam. 0.52-0.5 0.25 25-1.1 Mm. Mm. Mm.
Very Fine Sand Diam. 1-0.05 Mm.
Silt Diam. 0.050.005 Mm.
0.0050.000
0.0
20.4
24.8
36.0
18.8
0.2
3022
14.6
21.0
34.0
6.4
36.6
20.2
27.6
6.2
0.6
35.0
18.9
19.5
25.5
MATERIALS ANALYZED 1-Florida pebble phosphate (Gnely ground) ...... . . . . 0 . 0 2-Mine-run phosphate from -hard rockregions 0.0 3-Sam~le 1 mixed with h e l y ground silicaandcoke . . . . 3 . 2 4-Sample 2 mixed with Gnely ground silica and coke .... 0 . 4
......
Clay Diam.
Mm.
I n order t o compare t h e fineness of t h e washed and ground pebble phosphate with t h a t of t h e mine-run phosphate, samples of each were ground in a ball mill and then submitted t o t h e mechanical analysis employed in this Bureau in connection with t h e classification of soil types. Samples of these two phosphates mixed with t h e proper proportions of finely ground sand and coke t o produce a charge suitable for furnace treatment were also analy.zed in t h e same way. For results of these mechanical analyses see Table 11.
T H E J O U R N A L OF 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
.July, 1920
This table will show t h a t t h e percentage of clay particles present (upon which t h e plasticity of t h e material largely depends) was nearly twice as great in t h e mine-run phosphate as in t h e sample of pebble phosphate, even after t h e two materials had been ground for several hours in a ball mill and passed through a 60-mesh sieve. Experiments were then undertaken in briquetting samples of t h e original mixture except t h a t t h e finely ground pebble phosphate was replaced in part and finally wholly b y t h e mine-run phosphate. These charges in each case were mixed with I O per cent of water and made into short cylindrical briquettes (I in. in diameter) under a pressure of one ton. T h e results of these tests’ are given in Table 111. TABLE 111-SHATTER TESTS O N BRIQUETTES Ratio between the Two Height a t Which the Phosphates in Charge, Per‘Cent Briquette Shattered, Feet Pebble Mine-Run Air Dried Oven Dried Phosphate Phosphate Briquette Briquette 3 100.0 0.0 90.0
10.0
75.0 50.0 25.0
25.0 50.0 75.0 100.0
0.0
3 4 6
7 10
I t is evident t h a t a charge containing from 2 0 t o 2 5 per cent of finely divided material classed as clay can be formed into very satisfactory briquettes, b u t i t was decided t h a t t h e size of those used in t h e first tests was somewhat small for furnace treatment, so a larger mold was made and a round briquette 2 in. i n diameter used in t h e next furnace experiment. The tediousness of preparing a sufficient number for a protracted run, coupled with a desire t o test thoroughly t h e efficiency of t h e natural binder, prompted t h e writers t o make arrangements with t h e Lehigh Coal and Navigation Co., of Lansford, Pa., t o use their coal briquetting machinery on this phosphate mixture. This company kindly consented t o t u r n over their briquetting plant for t h e experiment, and accordingly a half ton of t h e mixture was crushed t o pass a IOmesh screen, thoroughly mixed with I O per cent of water and shipped t o Lansford in air-tight barrels. Without any further treatment i t was charged into a screw conveyor and fed directly t o t h e hopper above a press of t h e Belgian Roll type. Very satisfactory briquettes in t h e shape of eggets ( 2 . 2 5 x 2 ’ x 1.5) were produced which on drying withstood a drop of 6 f t . upon a cement floor without shattering.2 DIRECT H E A T I N G OF B R I Q U E T T E D CHARGE
T h e furnace was then so modified t h a t a portion of t h e flames and hot gases of combustion from t h e oil burners would play up through t h e central shaft a n d t h u s heat t h e charge of briquettes directly. The burners were lighted a t 8 A . M. and r u n steadily until 6 P. M., when a reading with an optical pyrometer was made which showed a temperature of over 1300’ C. o n t h e hearth. A few lumps of coke were then dumped into t h e shaft followed by 3 2 lbs. of briquettes. Within I O min. fumes of phosphoric acid began t o be evolved, These early briquetting experiments were made by Mr. I,. A. Steinkoenig, who has since resigned from the Department of Agriculture 2 The writers wish also t o express their appreciation of the courtesy extended by the General Briquetting Co., of New York City This company not only made a number of experiments in briquetting the phosphate charge but also briquetted a ton of material used in later experiments.
649
and this continued for over an hour. ilt 7.45 P. M. a few more lumps of coke were added followed by 3 2 lbs. of briquettes. Copious fumes were evolved about 1 5 min. later which gradually grew less dense until a t 8 . j o P. br. (one hour later) another charge of 34 lbs. was added. This was followed by a fourth charge of 33 lbs. at 9.03 P. M. The heat was continued until 12:oo midnight when t h e optical pyrometer gave a reading of 1470’ C. on t h e hearth. The burners were then shut off and an attempt made t o t a p t h e furnace, without success, due t o t h e viscous nature of t h e slag produced. After t h e furnace had cooled down, t h e slag was dug out and its phosphoric acid content determined. An average sample of t h e slag showed 1 1 . 5 2 per cent P206 while t h a t which was more glassy and better fused contained only 3.53 per cent of PZO~. It was found t h a t some of t h e briquettes which had not been fused were covered with a thin white glaze. This glaze evidently protects t h e carbon in t h e mass from t h e oxidizing gases until fusion takes place, for upon breaking t h e briquettes t h e coke was found unaltered, although they had been in t h e furnace several hours.
FIQ.2-EFFECT
OF THE DIRECTOIL FLAME UPON PHOSPHATIC BRIQUETTBS JUST BEFORE FUSION TAEGS PLACE. NOTETHE UNALTERED C O K E CONTAINED WITHIN THE MASS
The effect of this direct heating on t h e briquettes before they are actually fused can be seen in Fig. 2 . On t h e right are t h e briquettes as they appear before being charged t o t h e furnace, and a t t h e left of t h e picture are shown those which have been exposed t o a high temperature for several hours b u t not sufficiently high t o cause t h e m t o melt. I n t h e center are shown some of these latter briquettes broken open. It will be noted t h a t there is a sharp line of demarkation between t h e thin glaze of t h e oxidized exterior of t h e briquettes and t h e interior containing t h e unaltered coke. It was unfortunate t h a t t h e furnace used was of such a type as t o be ill adapted t o t h e change from t h e indirect t o t h e direct method of heating t h e charge. This fact accounts in part for t h e long time required in attaining a smelting temperature. With a view t o overcoming this difficulty, firebrick “annexes” were built on each end of t h e furnace and t h e burners t h u s placed further from t h e charge chamber so t h a t t h e
6.50
T € I E JOI'K,V.IL
OF I N D U S T R I A L A N D ENGINEERING CIIEMISTRl'
oil would ha\-e a better chance for combustion. T h e iron plat,es holding the burners were replaced by cast iron water jackets t o avoid the danger of injuring t h e burners, and a coil of pipe imbedded i n a coke fire was also placed between the blower or fan and tlie furnace so t h a t the air required for the combostion of the oil could be preheated hefore it was delivered t o t h e burners. The first test ( S o . 2 , Table I V ) made with these changes in the furn:icc was unsnccessful due t o the cracking of the cast iron witcr jacket around one of the burners which made i t nccessarr t o close d o w n after a feu- hours' run. But the second run ( S o . 3 , Table I\') was very encouraging, sinc.e phosphoric acid was copiously evolved but the temperature attained was not quite high enough. The third test ( N o . 4, Table IT') was more successful while it lasted, hut during the last hour of the experiment thc charze chamber collapsed and the burners had t o be shut off before the last of the charge was fully smelted.
Yol.
12,
No. 1
connected with a Cottrell precipitator for the collection of the volatilized phosphoric acid. This furnace (shown in Fig. 3) holding 700 lbs. of charge was completed early in January 1920, but adserse weather conditions and certain necessary changes in the ecjuipment have delayed its running. Only one short test has been made so far, and the breaking of the belt t.o one of t h e motors made it necessary t o cut off the burners before the experiment was completed. The results obtained in this short run, hoi vinced the workers t h a t the form of the furnace is well adapted ior the purpose and the principle used apparently sound. It is expected t h a t interesting and valuable d a t a will he obtained within t h e next few months which will show the commercial practicability of this process. I
