January, 1927
INDUSTRIAL A N D ENGINEERING CHEMISTRY
of the purity of the product, other than the observation that the resulting mercury was brilliantly clean, were made because this still follows the principles already shown by others to produce pure mercury.
107
Acknowledgment The authors wish to express their thanks to the Ferro Enameling Company of Cleveland for their kindness in enameling parts.
Determination of Thoria in Tungsten Filaments’ By Dorothy H. Brophy and Charles Van Brunt GENERAL ELECTRIC Co., SCHSNBCTADY. N. Y.
as important. But unfortunately, the matter does not rest manganese, silicon, phosphorus, and other elements, here. I n collaboration with M. C. Lamar, it was soon disand the lack of complete information as to their genesis, covered (1912) that the unsatisfactory results yielded by character, and analytical behavior necessitate a careful this method were due to the complete volatilization of checking of all proposed methods for the determination of T h o z as chloride in a current of Clz carrying WCI6, the latter the purity of tungsten. This, in turn, calls for synthetic being changed to oxychloride, which also is volatile. This mixtures of known composition, and, in many cases, of a action of the WC16 is analogous to that of Sic14 on many oxides, history similar to that of those met in the field. Owing to except that in the case of SiC14 no oxychloride is formed, but the pressing demands of the industrial situation, the research non-volatile SiOz, or a silicate of the oxide acted upon. The oxychlorides of tungsten appear to have no effect as here reported was not carried very far forward when the need for it first appeared, and, indeed, has not yet been satis- chlorinating agents, and admixture of oxygen or air with the factorily completed. This, perhaps, is largely because evi- Clz effectually prevented the volatilization of the thoria dence rapidly accrued from other sources showed that prac- with the tungsten when the two were not mixed but merely tically all impurities were, or readily could be, eliminated in placed one after the other in the heated tube. Misgivings manufacture, combining, as this did, crystallization, pre- were felt, however, in regard to the application of this cipitation in strong acid solution, and finally, treatment in method to massive or filament tungsten containing thoria. hydrogen and in vacuo a t a temperature high enough to The reaction with tungsten is somewhat violent, and temperature control therefore difficult. Also mechanical losses volatilize nearly all other metals. Kew and more specific problems accompanied the dis- seemed possible. Actually, widely varying results were covery that the deliberate addition of certain refractory obtained on presumably homogeneous material. It was oxides would prevent “offsetting” or destructiye crystalliza- therefore deemed best to burn all samples to oxide in air or tion of the filaments in use. Later, by a process of survival, oxygen before chlorination. Carefully checked on mixtures thoria came to be used exclusively for this purpose. Within of known content, this method gave excellent results, I t s recent years, systematic research has been made on the disadvantage is that it is very tedious, many hours being effect of small additions of many elements. Methods of required for complete volatilization. Pinagel’s work4 had shown that volatilization in pure HC1 determination of small quantities of specific metals, usually singly, sometimes in pairs, in the presence of relatively large gas gave excellent results for the separation and estimation quantities of tungsten, have been devised. Papers on of minute quantities of silica in tungsten trioxide, and trial molybdenum2 and boron3 have already been published. seemed to confirm the idea that thoria, in common with other The present paper deals mainly with thoria, by far the refractory oxides, was unaffected by this treatment, while most important of the additions from a practicd standpoint, the removal of the tungsten was complete in a small fraction and the only one which has so far withstood the test of service of the time required with chlorine. This method then came into very general use among chemists engaged in lamp filain lamps. The most obvious method-solution in nitro-hydrofluoric ment work. Late in 1924, when much filament analysis, demanding a acid and precipitation as hydroxide-was quickly abandoned, because as a rule only very small quantities of material, high degree of accuracy, came into our hands, it fell under sometimes a single lamp filament, are available and because suspicion. It was found that satisfactory “checks” could the precipitate retains tungsten, necessitating retreatment. not always be obtained. I n practice, the heating in the gas Alternative dry methods, involving selective volatilization was usually terminated as soon as the residue in the quartz of the tungsten as chloride, promised manipulative advan- boat appeared white. On trial, however, a further loss ootages in dealing with minute quantities. The reactions in- curred on prolonging the treatment. This was a t first asvolved, however, have required much study, in the light of sumed to be due to residual tungsten, but later it was shown which the procedure has been modified from time to time. that thoria was being chlorinated and volatilized. The The earliest attempts were based on the fact that tung- rate is relatively slow, however, and to this must be ascribed sten metal is volatilized by moderate heating in a current of in part the useful service given in the past by this method. The data upon which this conclusion is based are given Clz, whereas ThOz is not. This, of course, involved the in Table I. assumption that the thorium is present as oxide in the filaThe addition of oxygen to the HC1 in about equal proporment. As the accepted theory of its functioning in the filament involves its presence as oxide, and as the percentage of tion prevented loss (Table 11). All the samples in Table I1 oxide is usually the thing sought, however, this was not regarded are residues actually obtained in analyses of tungsten wire. I n practice, i t is customary to make the first weighing as soon 1 Presented at the Intersectional Meeting of the American Chemical as the residue appears white, but the second weighing not Society at Niagara Falls, N. Y., January 29, 1926. Received July 1, 1926. infrequently shows a decided loss, due, no doubt, to traces 2 Hall, J . Am. Chcm. SOC., 44, 1462 (1922).
HE tendency of tungsten to form complexes with iron,
T
8
Brophy, I b i d . , 41, 1856 (1925).
4
Inaugural Dissertation. Bern, 1904.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
108
Maintain a temperature of 700" C. in the furnace. First heat the sample in oxygen until completely oxidized, usually overnight. The large increase in volume is taken into consideration in choosing the size of the sample. Then add dry HC1 gas to the oxygen in about equal proportion, and volatilize the tungsten trioxide as oxychloride, which usually takes about 2 hours. Then weigh the residue and report. The scale of the operations and the delicacy of the balance permit of a percentage accuracy not inferior to that obtained in the usual way with quantities ten times larger. A variant of this procedure, in which the preliminary oxidation is omitted, has been used, the metallic sample being treated directly with the mixed gases, oxidation and volatilization taking place concomitantly. The writers are not prepared to say that this modification is unreliable, but have felt misgivings about it. At considerably higher temperatures, a t least in hydrochloric acid gas alone, the reaction W 6HC1 = WCla 3Hr occurs readily enough, as is evidenced both by the color of the sublimate and by the presence of free hydrogen in the outflowing gas. The possibilities that it might occur to some extent at 700-800" C. with an insufficient excess of oxygen, as, for instance, in the interior of a pile of metal powder or of filament fragments, with resultant chlorination of some thorium, seemed not so remote as to justify us in giving up the safeguard of the preliminary burning to oxide, requiring, as it does, no attention on the part of the operator. Another modification, in which the vapor of chlorbform is substituted for hydrochloric acid, has been tried with equally good results. For example, a sample of T h o z weighing 0.01290 gram showed a gain of 0.00002 in a 2-hour ignition. Treated by the procedure described, unthoriated filaments ordinarily leave no weighable residue. This justifies the custom of accepting any residue as Thoz, although the chemist prefers to report his results simply as "non-volatile" to indicate that no attempt has been made to establish the exact nature of this residue by analysis. This is unsatisfactory from a scientific standpoint. To meet the situation and also to obtain data as to what the
of WOa. The ignitions recorded are for 1hour each a t 700" C. unless otherwise stated. in HCl G a s a t 700' C.
Table I-ThOz
TIME
WEIGHT Grams Sample 1 0.02228 0.02222 0.02170 0.01948 Sample 2 0.00082 0.00036 0.0002s 0.00004
Hours 0 1 4 6
0 0.5 2 3 Table 11-Weight SAMPLE
1 2 3 4 5 6 a
LOSS
Gram
0.00006 0.00058 0.00280 0.06646 0,00054 0.00078
of Oxide a f t e r Ignition
'2:gR
2 HOURS Gram
3 HOURS Gram
0.00094 0.00036 0.00044 0.00062 0.00070 0 05764
0.00038 0,00036 0.00020 O.OOOja8
0.00038 0.00020 O.OOOg8
0.05764
0 05764
+
No loss after 8 hours.
The reaction ThCla
+
0 2
& ThOz
+ 2C12
is apparently complete from left to right with a very moderate concentration of oxygen. This is evidenced also by the failure of T h o s to volatilize in chlorine gas. The rate of volatilization of the WOa is somewhat reduced by the oxygen addition, but is still much more rapid than in chlorine alone. The procedure in filament analysis is as follows: Break the filament into short pieces and introduce it into a clear quartz tube about 30 mm. long and 5 to 6 mm. in outside diameter. Slightly choke the ends of the tube by fusion to aid in retaining the sample. The empty tubes weigh about 0.5 gram. Take their weight before and after filling upon an assay balance sensitive to 0.01 mg. Place the filled tube in a small quartz boat and introduce into a larger tube of clear quartz, which, in turn, is inserted into a special electric heater so constructed that the sample can be inspected a t any time by simply raising a cover.
GASUSED
TIME WEIGHT OF OXIDE
Hours
Gram
Tantalic oxide
...
HCI HCl
+ Oa
C1
CHClr
+ 02
HC1 HC1
+ On
CI CHClr
+ 0:
HCI
HC1
O
+ On
0.05004 2 0.03920 1 0.03612 ... 0.00560 1 0.00546 3 0,00442 ... 0.01546 7 0.01532 5 0.01530 7 0.01520 6 0.01518 0.05658 2 0.08602 Titanium oxide ... 0.00856 3 0.00230 0.00706 1 0.00698 2 0.00674 1 0.00660 ... 0.00544 4 0.00502 6 0.00486 .1. . 0.00432 0.00412 1 0.00408 2 0.00400 Zirconium oxide ... 0.01588 1 0.01472 1 0.01334 1 0.01288 1 0.01198 0.01406 1 0.01400 2 0.01400
Had sublimed in the tube.
... ...
...
DECREASE 7"Total
GAS USED
...
CI
22.0 28.0
...
2.5 3.4
CHCl3
...
+ Oz
HC1
1.7 1.8
HC1
... , . .
+ Oz
CHCls
+ Oz
...
0.4 0.4
Zirconium oxide (Concluded) ... 0.00592 1 0.00672 1 0.00564 1 0.00554 1 0.00538 ... 0.00694 2a 0.00488 Ceric oxide ... 0.00476 1
..
1 1
... 2
2 2 Aluminum oxide
1
...
HCI
HCl
2
+ Oz
1 2
... 1
2
...
7.3 16.5 19.0 24.7
WEIGHT OF OXIDE Gram
1
...
5.1 6.0 7.9
TIME Hours
1
1,; 4.5 6.5
...
+
1 1
73.0
10.7
Vol. 19,!No.!l
1
1
1
c1 CHClr
,.
4
+ 02
6
... 2
0.00920 0.00808 0.00670 0.00506 0,00878 0.00940 0 00920 0 00916 0.01430 0.01504 0.01600 0.01496
0.00990 0.00968 0.00928 0.00844 0.00712 0.00724 0.00712 0.00690 0.00678 0.01172 0.01160 0.01160 0.02263 0.01320
DECREASE 5%Total
...
3.4 4.7 6.4 9.1
,..
29.5
.. . . ... ... , . .
...
2.2 6.2 14.6
...
1.7 0.0 3.1 4.8
...
1.0 1.0
...
42.0
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1927
109
volatilization has not been ascertained, however. I n the former case the method should be available for separation. As it stands it does not give quantitative results. Considered as criteria of the application of the various procedures to the quantitative estimation of the oxides these results in all but HC1 would often be satisfactory for small percentages. But in such cases the percentage losses would be likely t o be very much greater than here shown, for instance, sample 1 in Table I, which was from stock thoria, and sample 2, which was a residue from a separation from a relatively large quantity of tungsten with which the thoria had been incorporated in manufacture. I n such cases the residues are usually in the form of pseudomorphs, or rather phantoms, of the original wire greatly enlarged by the swelling accompanying oxidation, and therefore present an enormous surface to the action of the gas. As a large excess of the gas is always present,. it is reasonable to suppose that surface is the controlling factor in the speed of volatilization. I n thoria determinations, all of the oxides and the silica in any of the gases cause serious contamination of the thoria Table IV residue, for volatilization is never even approximately comLoss NOTOVER' GAS USBD plete. This means that the method for the determination of 2 per cent 10 per cent thoria in tungsten first described cannot safely be applied HC1 None None HC1 + 0% TiOz, ZrOr, Ah03 Taros to filaments of unknown composition without further operaClr Taros, AlzOs ZrOz CHC13 f Or TarOs Ti02 tions upon the residue. Although simple enough when plenty of material is a t hand, it cannot be used for residues of the The ceria results are inconclusive. Reduction was evi- size frequently met in actual practice. Owing to the high dent with HC1. The gain in weight in all the gases points degree of insolubility of nearly all of the oxides considered, to the formation of chloride. Whether this is incomplete even qualitative application of microchemical methods to without accompanying volatilization, or complete with some such residues is difficult.
method would indicate if certain refractory oxides other than T h o , were present in filaments of unknown composition, Ta205,Ti02, ZrOz, CeOz, and A1203,were studied to determine their behavior on heating in Clz, HCl, HC1 02, and CHCI, 02.The apparatus and procedure used for thoria were employed. As Pinagel's4 work has fully covered the behavior of silica in the presence of \NO3, it was not considered necessary t o repeat it. The fact that silica is wholly stable is important mainly because it may be an accidental impurity in filament tungsten. Unfortunately, the "fuming off" process with HF cannot be applied for its removal from other oxides in the case a t hand, because of the inconstancy in weight of platinum when heated in mixtures evolving even traces of CL. Transfer of the residues, owing to their minuteness and physical character, is impracticable. The behavior of the oxides studied is given in Table 111. If the total time of heating is not more than 3 hours, the loss shown in Table IV results.
+
+
Conversion of Fibroin,' Chitin, Casein, and Similar Substances into the Ropy-'Plastic State and Colloidal Solution' By P. P. von Weimarn E(oGYoSHIKENSHO,
S EARLY as 1912 the writer3 established the fact that aqueous solutions of any readily soluble salt capable of strong hydration possess the ability to convert cellulose into the plastic state and to produce the colloidal dispersion of cellulose. The concentration of the solut'ion, the temperature a t which the dispersion of cellulose proceeds, and the time necessary to complete the dispersion vary with the salt taken, its solubility, and its degree of hydration. If by the ability of salts to produce dispersion (designated by the symbol D ) we underst'and the magnitudes directly dependent on the average rates of dispersion of the same kind of cellulose (other conditions being equal), then the following series of inequalities4 lvould be both theoretically and experimentally established for certain lithium and calcium salts :
A
DLicss
>
DLiI
D c ~ ( c N s )>~ Dcalz
> >
DL~B~
D c ~ B ~ ~
Japanese Patent Application; patentee, Imperi'il Industrial Research Institute of Osaka; inventor, €'. P . von Weimarn; date of invention, December, 1926. Patent application cause of several months' delay in publication of results obtained by writer. 2 Received July 27, 1926. 8 R u s s i a n Chem. SOL, 44, 772 (1912); Kolloid-Z., 11, 41 (1912); English translation in Repls. I m p . I n d . Research Inst. Osaka, J a p a n , 4, No. 7, 17 (1923). 4 von Weimarn, J . Ckem. Educotiun, 3, 378 (1926). 1
D A I N l , OSAK.4,
JAPAS
These six salts are examples of salts with high dispersion abilities. I n 1913 the author5 announced that in theory aqueous salt solutions are able of dispersing not only cellulose, but also other dispersoids capable of hydrolysis into solubIe products. I n other words, such organic colloids as fibroin (the chief constituent of natural silk), chitin (containing nitrogenous polysaccharose-i. e., the nearest analog t o cellulose, the chief constituent of the shells of cuttlefish (sepia), crayfish, crabs, lobsters, beetles, etc.), and similar colloids, are also convertible by means of concentrated aqueous salt solutions into the ropy-plastic state and into colloidal solutions, Fibroin
This theory was not proved experimentally by the author until the middle of December, 1925, with fibroin, and, in collaboration with Utzino,6 a t the beginning of 1926 (February-March) with chitin, casein, fibrin, and keratin. Fibroin (silk wadding being used for experimentation) proved to possess a considerably higher colloidal dispersa5 Ann. SI. Petnsburg Mining Inst., 4, 151 (1913); German translation, Kolloid-Z., 29, 198 (1921) ; English translation, Refits. I m p . I n d . Research Inst. Osaka, J a p a n , 4, No.7, 23 (1923). I n the laboratory of physical chemistry, Imperial University of Kioto, S. Utzino is now submitting to a special study the hydrolytic action of concentrated aqueous solutions of neutral salts upon the substances mentioned above.
.
