1091
V O L U M E 25, NO. 7, J U L Y 1 9 5 3 ing apparatus shown in Figure 12. I t consists of a base, K , into which are threaded the four posts, L. Over these posts are slipped matched springs, M , whose total load capacity is about 40 to 50 pounds. On top of these springs is placed the cup holder plate, F, shown in Figure 2, after four holes have been drilled in it so as to slip over the posts.
as in the effect of solids content upon this property. Depending on the latex, dilution may decrease or increase stability, or the stability may pass through a maximum a t a particular concentration. KO explanation is available a t present for the mechanical stability behavior of the various latices. It is quite certain, however, that the test described here does not involve plastometer action. During the running of the test the indicator on the scale remains constant to ca. *O.l pound. If coagulum accumulated under the rotor and plastometer action entered, the load would rise appreciably. As this is not observed, plastometer action cannot be responsible for the results obtained, and an explanation has to he sought in the colloidal character of the latices. ACKNOW LEDGMEKT
Figure 12. Simplified Loading Mechanism for Mechanical Stability Tester
A rule mounted in front of the loading apparatus permits determination of the state of loading of the springs. To obtain the desired loading, the rup and 25 pounds in weights are placed on plate F , and the depression of the springs is observed on the rule. Pressing the rotor against the cup bottom until this reading is reproduced will give then the 25-pound load required for the test operation. COICLUSIOhS
The new test described for the determination of the mechanical stability of rubber latices is rapid, reliable, and reproducible to within 5%. I t is applicable to both natural and synthetic latices. L-sing this test, a study has been made of the effect of solids content on the mechanical stability of a natural latex and eleven synthetic latices of various types. The results show that the various latices differ considerably in mechanical stability as well
The work discussed herein was performed as a part of the research project sponsored by the Reconstruction Finance Corp., Office of Synthetic Rubber, in connection with the government synthetic rubber program. LITERATURE CITED
(1) Crude Rubber Committee, Division of Rubber Chemistry, Rubber Chem. and Technol., 14, 299 (1941). (2) Davey, W.S., and Coker, F. J., Trans. Inst. Rubber Ind., 13, 368 (1938). (3) Dawson, H. G., AXIL. CHEM.,21, 1066-71 (1949). (4) Jordan, W. F., Brass, P. D., and Roe, C. P., IWD.ENG.CHEM., - 4 N I L . ED.,9, 182 (1937). (5) Madge, E. W., Trans. Inst. Rubber Ind., 28, 207 (1952). (6) Madge, E. W., Collier, H. M., and Duckworth. I. H., Ibid., 28, 15 (1952). Rubbe? Chem. and Technol., 12, 893 (1939). (7) Murphy, E. -4., (8) Noble, R. J., “Latex in Industry,” New York, Palmerton Publishing Co., 1936. (9) Novotny, C. K., and Jordan, W. F., IXD.ENG.CHEY.,ANAL.ED. 13, 189 (1941). RECEIVEDfor review December 8, 1952. Accepted March 5 , 1353.
Quantitative Organic Precipitants for Osmium I. HOFFILIN, J. E. SCHWEITZER, D. E. RYANL, AND F. E. BEAMISH C-niversity of Toronto, Toronto, Ont., Canada This research arises from a general investigation of the characteristics of organic precipitants for the platinum metals. The results obtained with osmium were of some significance because organic reagents have not been used successfully for the gravimetric determination of osmium; indeed no approved microgravimetric method for osmium has been recorded. The present report deals with the successful application of a substituted thiazole and
T
HESE investigations were made to develop a microgravimetric procedure whereby osmium in ores could be determined after extraction by fire assay, with lead as a collector. Allan and Beamish ( 1 ) used a hydrolytic procedure for micro quantities of osmium based on the method used by Gilchrist ( 3 ) for macro amounts, but reported a significant error, characteristic of “hydrolytic methods.” True blanks could not be determined owing to retention of osmium by the residue after oxidizing ignitions. Although certain organic reagents for the precipitation of osmium had been discovered by the authors they were not applicable because the precipitates could not be purified by washing, and ignition in air was inadmissible. However, the observation had been made in this laboratory that palladium dimethyl1 Present address, Dalhousie University. Halifax, N. S.. Canada.
indicates the applicability of certain substituted thioureas and thiazoles to colorimetric or gravimetric determinations. The use of strychnine sulfate as a gravimetric reagent and a completed procedure for the precipitation of the osmium-thionalide complex are reported. Besides providing the first gravimetric organic precipitants for osmium, the data obtained indicate the direction to be taken in the search for new reagents for the platinum metals.
glyoxime could be ignited in hydrogen to produce the metal (6). It is probable that palladium acts as the catalyst for this reduction. Osmium is known as an active catalyst, and it seemed likely that the metal could be recovered from organic complexes in a similar manner. Allan and Beamish ( 1 ) made preliminary tests on the possible use of thionalide as a precipitating reagent. The authors record below their data on the efficiency of thionalide, 2-phenylbenzothiaeole, and strychnine sulfate, and their successful application of these compounds to the determination of osmium. DETERMINATION OF OSMIUM
By Thionalide. REAGENTS. Ammonium Bromo-osmate. A purified sample of ammonium bromo-osmate was analyzed for
1092
ANALYTICAL CHEMISTRY
osmium content by reduction to constant weight in hydrogen, ignition in air, followed by reduction in hydrogen. No residue remained after oxidation. Three determinations showed the osmium content to be 26,98Yc (theoretical 26.95%). Thionalide (Thioglycolic-p-aminonaphthalide). The thionalide used was prepared by a method developed in this laboratory and recorded by Welcher (8). PROCEDURE. Weighed samples of ammonium bromo-osmate were dissolved in dilute hydrochloric acid (0.5 N ) , and the total volume was made up to 50 ml. with the same acid. An excess of the calculated amount of thionalide was dissolved in 15 ml. of alcohol, and added dropwise to the gently boiling solution over a period of about 30 minutes. A buret with the tip extending into the hole bored in a borosilicate watch glass was found very convenient for thia slow addition. It was found necessary to boil the contents of the beaker for approximately 2 hours to give a well-coagulated precipitate and a clear supernatant liquid. Heating was continued on the steam bath for an hour. Constant volume was maintained by additions of water when necessary. The supernatant liquid was decanted through a porcelain crucible of A2 porosity which had previously been heated in hydrogen to constant weight. A rubber policeman was cut down to a small tip and used to transfer the precipitate to the crucible. The remaining particles were recovered by repeated washings with 0.2 AT hydrochloric acid solution. The crucible was placed in the clear quartz ignition tube, and hydrogen was allowed to flow for 5 minutes before ignition. Organic matter was then slowly burned off with a low flame, and finally ignition was continued about 2 hours with the full heat of a M4ker burner, The crucible and contents were cooled in hydrogen and nitrogen, placed in a constant humidity desiccator (7) for 10 minutes, and weighed after remaining in the balance case for 20 minutes. Ignition in hydrogen was repeated to constant weight, and finally the osmium was volatilized as osmium tetroxide by heating in a muffle furnace under the fume hood for 1 hour at 750" C. The residue was ignited in hydrogen and weighed to constant weight as described above. Spectrograms of the residue revealed iron, silicon, copper, and magnesium, but no osmium. Magnesium was used as a catalyst in the preparation of thionalide. METHODOF TESTING FILTRATES. The filtrate and washings were slowly boiled with 20 ml. of 30% hydrogen peroxide and a few milliliters of concentrated hydrochloric acid solution in an Erlenmeyer flask fitted with a ground glass connection and attached to a bubbler tube containing about 15 ml. of 10yc thiourea in 6 N hydrochloric acid solution. The bubbler tube was connected to an aspirator, and air was drawn through the apparatus to carry the vapors into the thiourea solution. The osmium content was estimated visually by comparing the intensity of the red color with a set of standards. The limit of sensitivity for this test was 12 micrograms. Filtrate losses in all cases were less than 12 micrograms. Results obtained are recorded in Table I.
Table I. Determination of Osmium by Thionalide Weight of
os
(NHdzOsBr6,
Taken,
Mg. 105.70 95.75 50,33
Mg.
35.65
22,52 17.92 18.39 9.34 7.80 8.02
28 52 25 83 13.58 9 62 6 07 4 83 4 96 2 52 2 11
2.16
os
Recovered, Mg. 28 44 2 5 91 13 51 9 59 6 01 4 81 4 94 2 50 2 09 2 14
Absolute Error, hlg. -0 08 1 0 08
-n
-0
07
03 -0 06 - 0 02 -0 02 - 0 02 - 0 02 -0 02
DETERMINATION O F ORGASIC cONSTITVENT-oSl\.fICM RATIO. A4mmonium bromo-osmate was dissolved by heating in 957c alcohol, and the solution was filtered. Jf'eighed amounts of thionalide were dissolved in warm alcohol and added dropwise to the gently boiling bromo-osmate solution. The resulting precipitate was recovered on a small Berlin A2 filtering crucible, washed well with alcohol, dried a t 110' C., and weighed. The osmium content was found by reduction to constant weight in hydrogen, and the residue was determined after oxidizing ignition in air, and subsequent reduction in hydrogen. The weights of osmium recovered from 9.53 mg. and 10.51 mg. of complex were 2.18 mg. and 2.39 mg., respectively. These indicate a ratio of one atomic weight of osmium to three formula weights of thionalide. This was rather unexpected since 1:2 was the ratio in the ruthenium complex (6).
Table 11. Organic Reagents for Osmium Reagents Substituted thiazoles 2- Aminobenaothiazole 2-Aminothiazole 6-Amino-2-mercaptobenzothiazole 2-.lmino-4-(p-diphenyl) thiazole 2-Ethylmercaptobenzoxazole 2-Hydroxyphenylbenzoxazole 2-Rlercaptobenzoxazole 2-MercaDtobenzothiazoIe
Medium, HC1 0.05 N 4N 001 001
D
B
B
C C col C
B
2-Phenylbenz othiazole Substituted thioureas 3-Diphenylthiourea Diphenylthiocarbazide S-di-n-tolvithiourea
B
C
D D D
col
A
A Brucine B p-Kitrobenzene-azo-1-naphthol B a-Sitroso-2-naphthol A 1.10-Phenanthroline Strychnine sulfate A A B C and D refer t o quantities of osmium found in the filtrate. A , nonddtec'table; B , 20 t o 40 micrograms; C, 40 t o 100 micrograms; D , greater than 100 micrograms: col, color.
Qualitative Experiments on Organic Precipitants for Osmium. Arising out of the following general investigation of the structural characteristics of organic reagents necessary for the precipitation of platinum metals, there appeared a number of reagents particularly suitable for the precipitation of osmium.
A solution of osmium was prepared by dis EXPERIMENTAL. solving osmium tetroxide in 6 X hydrochloric acid, freshly saturated with sulfur dioxide. The solution was allowed to stand overnight in a glass-stoppered bottle and then evaporated almost to dryness six times with concentrated hydrochloric acid, to eliminate sulfites, then made up to a volume of 1 liter with 6 N hydrochloric acid. The solution contained approximately 1.5 g r a m of osmium. A 25-mI. aliquot was diluted and acidified to one of the acid conditions shown in Table 11. An alcoholic or aqueous solution of the organic precipitant uqder investigation was added dropwise to the gently boiling solution. Boiling was continued for 2 hours and, if a precipitate had formed, heating was continued on the steam bath for 1 hour. Constant volume was maintained by additions of water when necessary. The reaction mixture was set aside to cool and settle. The precipitate was recovered by filtration on a Berlin crucible of A2 porosity and the filtrate was ksted for osmium as descnbed above. Some fifty organic reagents were tested in this way and of these the reagents listed in Table I1 may prove suitable for quantitative determination of osmium either by gravimetric or colorimetric methods. The reagents and results obtained are lieted in Table 11. By Strychnine Sulfate. Because of the lack of agreement in the literature concerning the suitability of strychnine sulfate as a precipitating reagent for osmium, it was included in this investigation. Ogburn and hliller ( 4 ) reported that osmium was completely precipitated as a canary yellow complex when a saturated aqueous solution of strychnine sulfate was added to a slightly acidified solution of sodium chloro-osmate (Xa20sC16). The authors stated that the compound contained neither chlorine nor sulfate and that it was probably composed of one atom of osmium combined with three strychnine radicals ( C21H~20~N2)30~. The osmium content of this postulated formula is 15.99% but Ogburn and Miller obtained 17.58%. Gilchrist (3) used weighed portions of ammonium chloroosmate and of ammonium bromo-osmate t o test the method of Ogburn and Miller but found that the filtrate invariably contained osmium, He stated that different complexes were formed from the two salts, and reported the approximate osmium contents as 15.8% and 19.1% for the bromo-osmate and chloro-
V O L U M E 25, N O . 7, J U L Y 1 9 5 3
1093
was dissolved in water and the canary yellow compound was osmate complexes, respectively. Contrary to the findings of precipitated with an aqueous solution of strychnine sulfate and Ogburn and Miller, Gilchrist found considerable amounts of recovered and purified as described under the hexabromo comhalogen, and suggested that the complexes formed might be plex. The osmium content was found to be 1i.3170, These strychnine bromo-osmate (CnlHz202?J*)2.H20sBrB (14.19% osresults confirm the findings of Ogburn and Miller. mium) and strychnine chloro-osmate (C~1H220~N2)z.H20sC1s The canary yellow chloro complex was also precipitated from a n osmium solution prepared as described above. The average (17.71 yo osmium). Since strychnine sulfate gave incomplete of four determinations was 17,5270 osmium with a standard precipitation, and since the precipitates appeared to have indeviation of 0.06%. The chlorine content as determined by constant composition, Gilchrist concluded that precipitation by bomb explosion was 19.257, and by difference the strychnine content was 63.23%. These results indicated the following empirical strychnine sulfate was not a reliable procedure for the deterformula: osmium (1.00), strychnine (2.01), and chlorine (5.90). mination of osmium. The results obtained by the authors and recorded in Table I11 The empirically determined formulas for the hexachloro- and prove that strychnine sulfate can be used for quantitative prehexabromo-osmium complexes lend support to the assumptions cipitation. made by Gilchrist regarding their compositions. Table 111. Determination of Osmium by Strychnine Sulfate Weight o (NHdzOsBr,,,
Weight of OS Taken, 1Mg.
Weight of Os Recovered,
Absolute
Mg
62.45 62.76 54.10 43.65 41 31 39 11 33 60 24 03 23 44 20 45 17 12 15 06
16.85 16.93 14.60 11.77 11.14 10 55 9.06 6 48 6 32 5 52 4 62 4 06
16.82 16.96 14.55 11.72 ii.11 10.60 9.01 6 43 6.30 5.53 4.60 4.07
-0.03 +0.03
hfg.
Error, Mg. -0.05
-n
0.i
-0 03
+O -0 -0 -0
05 05 05 02 +o 01 - 0 02 +o 01
REAGENTS. Strychnine Sulfate, B.P.C., U.S.P. The British Drug Houses, Ltd.; London. Hydrobromic Acid, c.P., 48%. J. T. Baker Chemical Co. This acid is referred to in the text as hvdrobromic acid and was purified by distilling twice, the first an& last portions being discarded. Sulfur Dioxide-Hydrochloric Acid Solution. This solution was made by saturating 6 N hydrochloric acid with sulfur dioxide at room temperature. PRECIPITATION OF OSMIUM BY STRYCHNINESULFATE. Weighed samples of ammonium bromo-osmate were dissolved in about 50 ml. of water, and an aqueous solution containing an excess of the calculated amount of strychnine sulfate was added. The red-brown complex formed immediately, but coagulation was hastened by placing the beaker and contents on the steam bath for several minutes. After a period of cooling and settling, the precipitate was recovered by filtration on a tared crucible of A2 porosity. The last particles were transferred to the crucible by repeated washings with small amounts of dilute hydrochloric acid solution (0.02 AT). The organic matter was carefully burned off in the ignition tube in a n atmosphere of hydrogen as described previously. It was found advantageous to "play" the low flame a t the top and aide of the crucible when burning off organic matter. In this manner a slow, progressive charring was effected. Filtrates and washings were tested in the same manner as described for the thionalide precipitation, and losses in all cases were less than 12 micrograms of osmium. Spectrograms of the residues remaining after volatilization of the osmium revealed iron, silicon, copper, but no osmium. Table I11 shows the results that were obtained. COMPOSITIONS OF THE OSMIUM-STRYCHNINE COMPLEX.Hexabromo Complex. Purified ammonium bromo-osmate was dissolved in water and the red-brown complex was precipitated with an aqueous solution of strychnine sulfate. The complex was recovered on a tared Berlin A2 crucible, thoroughly washed with hot water, dried in the oven at 110" C. for 1 hour, and weighed to constant weight. Reductions in hydrogen and ignitions in air were made in the usual manner. The average of six determinations was 13.7770 osmium with a standard deviation of 0.1070. A halogen determination made according to the bomb explosion method of Beamish ( 8 ) showed 36.89y0 bromine. By difference, the strychnine content was 49.34yc,. The empirical formula indicated by these results is osmium (1.00), strychnine (2.03), and bromine (6.38). Hexachloro Complex. Sodium chloro-osmate was prepared by heating osmium sponge with sodium chloride in a stream of chlorine and was then extracted with purified absolute alcohol. The solution was filtered and the solvent was evaporated a t room temperature under reduced pressure. The chloro-osmate
By 2-Phenylbenzothiazole. Since the precipitation of osmium by 2-phenylbenzothiazole was complete, a detailed examination was made with a view to its use as a gravimetric reagent. REAGEKTS.2-Phenylbenzothiazole. The E y t m a n Kodak Co., Rochester, N. Y. Melting point, 114" to 115 Ammonium Chloro-osmate. A purified sample of ammonium chloro-osmate was analyzed for osmium content by reduction to constant weight in hydrogen, ignition in air, followed by reduction in hydrogen. No residues remained after oxidation. Three determinations showed the osmium content to be 43.28% (theoretical 43.32%). PRECIPITATION O F OSMIUM BY 2-PHENYLBENZOTHIAZOLE. Weighed samples of pure ammonium bromo-osmate were dissolved in about 25 ml. of 4 S hydrobromic acid, and an excess of the calculated amount of 2-phenylbenzothiazole, dissolved in 25 ml. of 4 N hydrobromic acid, was added. The dark red compound formed immediately a t room temperature. The mixture was allowed to settle and the precipitate was finally recovered by filtration on a tared crucible of A2 porosity. The last particles were transferred to the crucible by means of a thin glass stirring rod and by repeated washings with small amounts of dilute hydrochloric acid solution (0.2 -V). The organic matter was carefully burned off in the ignition tube in an atmosphere of hydrogen as described previously. On ignition of the preci itate, it had a tendency to li uefy. Any losses of osmium &e to this liquid passing through &e porcelain filter were overcome by placing the crucible on a small porcelain cap. Both the porcelain cap and the crucible were previously heated to constant weight in hydrogen. I n strong hydrobromic acid solutions the bromine evolved during the tests for filtrate losses vitiated the test with thiourea. Table IV shows the results that were obtained. COMPOSITION O F THE OSMIUM-2-PHENYLBENZOTHIAZOLE COMPLEX.Bromo Complex. Purified ammonium bromo-oshydrobromic acid and the dark red mate was dissolved in 4 precipitate was precipitated with less than the calculated amount of 2-phenylbenzothiazole, dissolved in 4 N hydrobromic acid. The complex was recovered on a tared Berlin A2 crucible, thoroughly washed with hot 4 hydrobromic acid, dried in the oven a t 110" C. for 1 hour, and weighed. Reductions in hydrogen and ignitions in air were made in the usual manner. The average of three determinations shows the osmium content to be 16.76% with a deviation of 0.03%. The bromine content determined by bomb explosion was 42.11%, and by difference the 2-phenylbeneothiazole content was 41.13%. The empirical formula for the complex indicated by these results is osmium (1.00), 2phenylbenzothiazole (2.21), and bromine (5.97). Chloro Complex. Puream monium chloro-osmate was dissolved in 4 N hydrochloric acid and the yellow complex was precipitated with 2-phenylbenzothiazole dissolved in 4 dY hydro-
.
Table IV. Determination of Osmium by 2-Phenylbenzothiazole Weight of (NHn)rOsBrs, Mg.
12.87 15 79 28.00 32,78 44.58 04.22 55.25 65.88 68.72 75.45 99.87
os
Taken, 5Ig. 3 47 4 26 7 55 8 84 12 04 14 63 14 90 17 77 18 54 20 36 26 94
os
Recovered, hlg. 3 4 7 8 12 14 14 17 18 20 26
45 20 54 79 03 60 90 73 48 33 95
Absolute Error,
Mg.
-0 -0 -0 -0 -0 -0 0 -0 -0 -0
+o
02 06 01 05
01 03 0 04 06 03 01
ANALYTICAL CHEMISTRY
1094 Table V. Receiving Solution SOz-HC1 S0z-HC1 HBr HBr HBr
Weight of (NHhOsBrs. l f g. 42.23 28.54 24 63 29.29 26.63
Taken, Mg. 11.39 7.70 6,64 7.90 7.19
HBr
16.25
4.38
16.62 45.58
4.49 12.29
HBr HBr
Osmium Distillations
Os
Organic Precipitant Thionalide Thionalide Thionalide Thionalide Strychnine sulfate Strychnine sulfate Strychnine sulfate 2-Phenylbenzothiazole
Precipitant. Mg.
Osmium Volatilized, Mg.
105 96 80 80 90
11.41 7.64 6.62 7.88 7.20
60
4.46
60 80
4.50 12.28
chloric acid. The complex was recovered and purified as described under the hexabromo complex, except that hot 4 W hydrochloric acid was used as wash solution. On reduction of the complexes in hydrogen, the average of two determinations showed the osmium content to be 22.18% with a deviation of 0.0170. The chlorine content, determined by bomb explosion, was found to be 24.91%, and by difference the 2-phenylbenzothiazole content was 52.92yob. The empirical formula indicated by these results is osmium (1.00), 2-phenylbenzothiazole (2.15), and chlorine (6.04). DETERMIVATION OF OSMIUM AFTER DISTILLATION
Sitric acid is used to dissolve lead buttons containing platinum metals. I t is also used sometimes to separate osmium from ruthenium by selective distillation. Since it is an interfering reagent for the precipitation of osmium, it was desirable to find whether these organic reagents could be used for the determination of osmium after nitric acid distillation. Two receiving media, hydrobromic acid and sulfur dioxide-hydrochloric acid solution, were used in the investigation. Apparatus. A detailed description and diagram of the apparatus used is given by Allan and Beamish ( 1 ) . It was found that the trap was unnecessary and it was used as an additional receiver, Distillation into Sulfur Dioxide-Hydrochloric Acid Solution. The four receivers were filled with 200, 150, 15, and 10 ml. of sulfur dioxide-hydrochloric acid solution, respectively, and about 10 ml. were placed in each of the flushing tubes. Forty milliliters of 1:1 nitric acid were added to the reservoir above the distilling flask, and ice baths were placed under the first two receivers. Weighed samples of ammonium bromo-osmate were dissolved in water and transferred to the distilling flask. Air was drawn slowly through the system, and the nitric acid was allowed to flow into the distilling flask. Heat was applied until the solution was boiling gently, and distillation was continued for about 45 minutes. The flame was removed, and air was drawn through the system for an additional 10 minutes before the contents of the receivers were rinsed into a large Erlenmeyer flask. The flushing solutions, followed by water rinses, were allowed to flow through the delivery tube into the Erlenmeyer flask, and it was then covered and set aside overnight (I ). The efficiency of the distillation was checked by testing for residual osmium in the distillation flask as described previously for filtrate tests. The content of the Erlenmeyer flask was transferred to a liter beaker, evaporated slowly to a small volume on the hot plate, washed into a small beaker with about 10 ml. of concentrated h drochloric acid, and again evaporated to a small volume. Tzree further additions of acid, followed by evaporation to a small volume, assured the destruction of sulfites. The concentrated solution was transferred to a 250-ml. beaker, and water rinses were added until the total volume was about 50 ml. Because filtration of osmium solution introduces considerable difficulty, and because true blanks could be easily obtained, it was decided to omit filtering the concentrated solution. Osmium was now precipitated by the organic reagents. Distillation into Hydrobromic Acid. The distillation process into hydrobromic acid was similar except that 70, 35, 10, and 10 ml. of acid were laced in the receiving flasks. An aging period was not requireg with hydrobromic acid. The receiving solutions were slowly evaporated to a small volume. The concentrated solution was taken up with about 50 ml. of water, and osmium was precipitated by the organic reagents. Procedure. PRECIPITATION BY THIONALIDE. The procedure as described above u7as followed for both the sulfur dioxidehydrochloric acid and hydrobromic acid distillates.
Absolute Error +0.02 -0.08 -0.02 -0.02
P R E C l P I T h T l O N BY STRYCHNINE SULFATE. It was found that the precipitation of osmium by strychnine sulfate was not complete in acid media. The failure by Gilchrist (3) to obtain quantitative precipitation can perhaps be traced to this difficulty. Gravimetric recovery of osmium from the acidic distillates was obtained by the following procedure.
-0.01
An excess of the calculated amount of strychnine sulfate was dissolved in water and added to + O 01 the osmium solution obtained by distillation. Some -0.01 precipitation t’ook place immediately. Sodium bicarbonate solution, lo%, was t,hen added slowly from a buret through a bored watch glass while the content8 of the beaker were swirled. The approach of neutrality was indicated by a decrease in the amount of effervescence, at which time the bicarbonate solution was added dropwise, and the p H of the solution was tested externally with Hydrion indicator paper using a stirring rod drawn to a long narrow point. The beaker was set aside without the application of heat to allow the contents to settle. The precipitate was recovered, and osmium was determined as described previously. Excessive bromine evolved during tests for filtrate losses on hydrobromic acid solutions was found to destroy the thiourea in the bubbler tube. This difficulty was not experienced when the hydrobromic acid receiving solution was evaporated to a volume of 5 ml. In several such cases fairly large residues were obtained, but no osmium was revealed by spectrogram. PRECIPITATION BY 2-PHESYLBESZOTHI.4ZOLE. The osnliunl from the bromo-osmate salt was distilled quantitatively using (1 :1) nitric acid as the ovidizing reagent, and the procedure ae described previously was followed. Table V contains a summary of the results that mere obtained. 4-0.08
DISCUSSION
The methods of determination of osmium by strychnine sulfate and 2-phenylbenzothiazole present greater ease of operation and require less time than the thionalide method. However, the thionalide complex coagulates particularly well and less care need be taken with its ignition as compared with the ignition of the complexes formed with the other precipitants. The precipitation by strychnine sulfate has the disadvantage of being made in neutral or slightly acid media, in which case certain other metals may be simultaneously precipitated as the hydrated oxide. The procedure using 2-phenylbenzothiazole is made in a strongly acid medium and hence overcomes this difficulty. It is interesting to note that when osmium is precipitated by 2-phenylbenzothiazole from a weakly acidic solution, a black complex forms. This complex is being examined. Precipitations of osmium conipleves by strychnine sulfate and 2-phenylbenzothiazole from ammonium chloro-osmate solutions and from sulfur dioxide-hydrochloric acid distillates were incomplete and osmium could be detected in the filtrates. The error was of the order of 0.1 to 0.2 mg. and may be due to the greater solubility of the chloro complexes. This is being investigated further. It has not yet been found possible to purify the complexer formed, hence direct weighing is not feasible. ACKNOWLEDGMENT
The authors wish to express their appreciation to the Canadian Department of Agriculture for financial support and leave of absence given to I. Hoffman. LITERATURE CITED Allan, W. J., and Beamish, F. E . , . ~ N A LCHEM., . 24, 1608 (1952). Beamish, F. E., IND. ENG.CHEM.,ANAL.ED.,6, 352 (1934). Gilchrist, R., J . Research Natl. Bur. Standards, 6, 421-48 (1931). Ogburn, S. C . , and Miller, I. F.,J . Am. Chem. SOC.,52, 42-8 (1930). (5) Rogers, pi. J , Beamish, F. E . , and Russell, D. S., IND. ENQ. CHEM.,ANAL.E D . , 12, 561-3 (1940). (6) Teeter, K. G . , unpublished research report. (7) Thiers, R., and Beamish, F. E . , ~ ~ N A CHEM., L . 1 9 , 4 3 4 (1947). (8) Welcher, F. J . , “Organic -4nalytical Reagents,” New York, D. Van Nostrand Co., 1948. RECEIVED for review January 3, 1953. -4ccepted A p r l l 9 , 1953
(1) (2) (3) (4)
