INDUSTRIAL A N D ENGINEERING CHEMISTRY
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it in favor of this new octane number scale, but rather that everyone should establish the relationship between his own scale and this one which is expressed in terms of octane numbers, in order that all investigators may be enabled to get on a common basis of reference, or that all may begin to talk a common language. It is recognized that, since the method and the conditions of test have a considerable influence upon the results obtained, determinations in terms of octane number may be only approximate for the present. But when both a definite apparatus and a specific method of test shall have been chosen, it is expected that this difficulty will be largely or altogether overcome. Uniform Procedure
As a means of putting the matter of knock-testing on a sounder basis, the Bureau of Standards and the different cooperating laboratories have been investigating the effects of the outstanding variables that influence the measurement of detonation. These include such factors as speed, temperature, compression, spark timing, atmospheric conditions, mixture ratio, and the like. The results of some of this work have already appeared in the literature, and a symposium on it is scheduled for the next meeting of the Society of Automotive Engineers. Accomplishments of Subcommittee
On account of the considerable time necessarily involved in getting the engines and accessory equipment designed, built, and delivered to the respective laboratories, most of the testing work of the subcommittee has been done during the current year. The effectiveness of the experimental work at the Bureau of Standards during the period has been largely increased by the special contribution of $5000 for the support of this work by a number of interested oil companies. This endeavor differs from some of the previous work done under the auspices of the Cooperative Fuel Research Steering
Vol. 22, No. 12
Committee in that, although m usual the experimental work is centered primarily in the endeavor at the Bureau of Standards, it is also being actively participated in at the laboratory of each one of the subcommittee members. Once a tentative apparatus can be approved, it will probably be made generally available a t once without waiting for further developments. It is expected that thereafter the scope of experimentation within the two industries concerned on further phases of the problem will be greatly extended. As giving some indication of the amount of work that has already been done within the Subcommittee on Methods of Measuring Detonation, it may be said that since its organization (and up to September 15, 1930) the group has held twenty-two meetings. With very few exceptions these meetings have been held at the time and place of some other gathering, which has been attended by representatives of both of the two industries interested. Following custom, the meetings of the subcommittee have been opened to anyone who wished to attend, and they have been largely attended. At sixteen of these twenty-two meetings, there was a perfect attendance and a t none were more than two members of the subcommittee absent. Cooperation of British Group
The subcommittee is fortunate in having the cooperation in this endeavor of a similar group in England. The British group is composed of the following key members: A. E. Dunstan, of the Anglo-Persian Oil Company; F. H. Garner, of the Anglo-American Oil Company; and J. Kewley, of the Asiatic Petroleum Company. The importance of this international cooperation is twofold.' There is, first, the help that the British group will give in arriving at a sound method, and, second, the benefit of the comparability and interchangeability of data that will arise from the resulting universality of apparatus and method over a large portion of the world.
Preparation of Metal Powders b y Electrolysis of Fused Salts I I-T horiurn1 F. H. Driggs and W. C. Lilliendahl WBSTINGHOUSB L A M P C O M P A N Y , BLOOMBIBLD, Nb
HE successful application of the electrolytic method to the preparation of uranium (1) suggested the possibility of its use in the production of metallic thorium. The electrolysis of anhydrous thorium chloride in fused potassium and sodium chlorides was attempted by Moissan and Honigschmidt (3) in 1904. Graphite rods were used as electrodes and the salts were fused in a porcelain crucible. A spongy mass was obtained which consisted of a large amount of oxide. No analysis of other impurities such as carbon, silicon (from the crucible), etc., is given. Von Wartenberg (4) used practically the same method, but substituted a carbon crucible for the porcelain one used by Moissan and HonigSchmidt. The metal obtained analyzed 87 to 88 per cent thorium, with the remainder consisting of thorium oxide, iron, carbon, and silicon. The two chief difficulties which the above experimentera encountered were: (1) the introduction of carbon when a carbon cathode was used; (2) the difficulty in working with the unstable thorium salt (ThCl,), which is easily hydrolyzed
T
1 Received
September 23, 1930.
Ja
in air and volatile a t high temperatures. I n the work to be described a more stable thorium salt was used and the carbon cathode eliminated by substituting molybdenum, which does not alloy with thorium at the operating temperature of the bath. Preparation of Potassium Thorium Fluoride
It was first necessary to obtain a thorium salt which would be more suitable than thorium chloride for electrolysis in fused baths. To fulfil this requirement it should be anhydrous, stable in air, easily prepared, and dissolve in fused baths without decomposition. The double salt potassium thorium fluoride (KThFa) seemed to meet this requirement in every respect. This salt was prepared by dissolving 1000 grams of thorium nitrate (48% Thoz) in 5 liters of water, and adding 640 grams of potassium fluoride dissolved in 1000 cc. of water with constant stirring. The precipitate (KThF6) was allowed to settle and was washed by decantation until the wash liquors gave no test for nitrate. It waB then filtered and dried a t
December, 1930
INDUSTRIAL A N D ENGINEERING CHEMISTRY
125" C. for several hours. An analysis of this salt gave the following result: Found KThFs (calcd.)
POTASSICM Per cent 10 22 10.67
THORIUM Per cent
60 5 63 41
WATER Per cent Trace
...
Electrolysis
The initial experiments were carried out in a graphite crucible, 6 cm. in diameter and 15 cm. in depth, inside measurements. The crucible served as the anode and the cathode consisted of a molybdenum strip 0.05 cm. thick and 1.0 cm. wide suspended in the center of the crucible. The completely assembled apparatus was exactly like that described in the preparation of uranium (1). The first bath consisted of equal parts by weight of sodium and calcium chlorides. When the double fluoride (KThFs) was added to this melt and electrolyzed at 775" C., a deposit of metallic thorium formed on the cathode. However, there were two serious objections to the use of this bath. The yields of metal were poor, as calculated from the current efficiency, and the constant addition of the double thorium fluoride during continuous operation gradually increased the calcium fluoride content of the bath. Since this salt is insoluble in water, it became increasingly difficult to separate it from the metal powder during the subsequent washings. The next bath consisted of equal parts by weight of sodium and potassium chlorides. With an operating temperature of 750-775" C. good deposits were obtained upon the cathode and, owing to the absence of calcium fluoride in this bath, the metal powder could be very easily washed free from the adhering salts with water. Since the bath seemed promising from the standpoint of good yields and continuous operation, a series of runs was made upon a somewhat larger scale to determine the efficiency of this method and the quality of the product. A larger crucible capable of holding 1000 grams of the mixed alkali chlorides was employed and the molybdenum cathode measured 2.5 cm. in width with a total area of 50 sq. cm. in the bath, With a current of 45 amperes the current density approximated 90 amperes per square decimeter. Sixty grams of potassium thorium fluoride were added a t the start of the electrolysis, and a t the end of every 20 minutes' operation the cathode with the adhering metal was withdrawn. A fresh cathode was then inserted, 60 additional grams of thorium salt were added, and the electrolysis continued. After eight deposits had been obtained, the thorium metal was washed and purified to determine the percentage yield. Eight runs of 20 minutes each had produced 137 grams of coarse thorium metal, This corresponded to a current efficiency of 58 per cent without taking into account the weight of the extremely fine thorium powder. The difficulty of its subsequent purification did not make it worth while to recover as metal and i t was dissolved in acid and reconverted to potassium thorium fluoride, The current efficiency actually improved after the first two runs and the bath has been operated continuously for twenty runs without any decrease in the current yield. Puri5cation of Metal Powder
The deposit adhering to the molybdenum cathode consisted of thorium metal interspersed with solidified salts. This mass was broken off the cathode and dissolved in water. Since all the salts of the bath (with the exception of a small amount of undecomposed KThF5) were soluble in water, this served to remove practically everything except metal. The metal was then ground for several minutes in an agate mortar and vigorously washed with water to remove the extremely finely divided thorium as well as any carbon particles which may have been occluded in the deposit. The powder was then washed three times with a 1:10 solution of
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nitric acid followed by another washing with water. The last traces of moisture were removed by filtering, washing with alcohol and ether, and then drying in vacuo. Heat Treatment and Chemical Analysis
The purified powder obtained above has been utilized for making x-ray targets, sheet, and wire by pressing, sintering, and degasifying the powder in vacuo by the methods described in earlier publications (9). Electrolytic thorium is extremely soft, well-annealed samples having a hardness as low as D-10 on the Rockwell scale. Bars of this metal may be cold-worked to almost any extent without intermediate annealing. Thorium metal prepared by electrolysis was analyzed for carbon, silicon, and iron, the percentage of other impurities being negligible. CARBON-Carbon was determined by direct combustion using thorium metal powder and lead oxide. The carbon dioxide evolved was absorbed in standard barium hydroxide solution using a special type of Meyer bulb. The unused barium hyaroxide was titrated with standard hydrochloric acid in the presence of the precipitated carbonate. A series of check runs was made using Bureau of Standards steel and the accuracy found to be comparable with those methods involving weighing the carbon dioxide after absorption. SAMPLB Grams
CARBON
Pcr cent 0.025
3.0000 3.0000
0.012
Av.
0.019
*
0.005
Smcox-If thorium metal is treated with acids, either singly or in combination, considerable oxide is formed which does not dissolve even in concentrated acid. This large amount of insoluble oxide makes a direct determination of silica by the usual method difficult, especially if the silicon content of the metal is small. The following method waa used: The metal was dissolved in aqua regia and the solution taken to dryness baking at 130' C. for 2 hours t o dehydrate the silica. The residue was dried a t 110" C. and fused in a platinum crucible with four times its weight of potassium acid sulfate. The melt was extracted with hot water, the thorium oxide forming a double sulfate which dissolved readily. (Addition of 5 cc. of concentrated hydrochloric acid assisted solution of the oxide.) The insoluble silica was recovered by filtration and determined in the usual manner. SAMPLE Grams
Si02 Gram 0.0021
2,1110
SILICON
Pn cent 0.046 * 0.01
IRON-Iron was determined colorimetrically using potassium thiocyanate reagent. The color of the sample w t ~ compared with the color of a standard iron solution, using special Nessler tubes. SAMPLE Grams
4.0370
IRON Per cent 0.005
The principal chemical and physical properties of metallic thorium have already been listed ( 4 ) ,and the metal prepared by the electrolytic method described above compares favorably with the best samples produced by the calcium-calcium chloride reduction of thorium oxide. The electrolysis of fused salts has also been applied to the preparation of a number of other rare refractory metals. It is intended to publish these in the near future. Literature Cited (1) Driggs and Lilliendahl, IND.E N G . CHEM.,22, 516 (1930). (2) Marden and Rentschler, Zbid., 19, 97 (1927). (3) Moissan and Honigschmidt, Ann. chim. p h y s . , [SI, 8,182 (1905) (4) Wartenberg, v., 2. Elekfrochem.,16, 866 (1909).
