Qualitative Separations on a Micro Scale Analysis of the Tellurium and Copper Groups of A. A. Noyes and W. C. Bray BERL S. ALSTODT AND A. A. BENEDETTI-PICHLER, New York University, New York, N. Y.
of the tellurium, and the treatment with sulfur dioxide is repeated. No iridium is precipitated under these conditions. Scott (18) and McAlpine and Soule (16) claim that metallic iridium is precipitated by sulfur dioxide from hot solutions, but Fresenius (10) states that sulfur dioxide does not precipitate iridium from solutions of iridic chloride. The latter statement was confirmed by the authors’ experiments. Solutions of various amounts of iridic chloride in 12 molar hydrochloric acid, 2.7 moIar hydrochloric acid, and water were saturated with sulfur dioxide and heated under pressure. In none of the tests was a precipitate observed, although reduction from the iridic to the iridous state seems to take place, as is indicated by the change of color. In experiments dealing with the precipitation of tellurium from solutions containing large quantities of iridium, no indication of a coprecipitation of the latter element was obtained. On the gram scale, the black precipitate of tellurium serves as confirmatory test. I n microprocedures, however, some extraneous material may be introduced in the various treatments and assume the appearance of elementary tellurium. An additional confirmatory test appeared advisable and the slide test described by Short (19) has been adopted for this purpose. Hillebrand and Lundell (IS), listing the behavior of chlorides in the “ether extraction method”, state that 5 per cent of the iridium is extracted as iridic chloride. Experience has shown that the amount extracted cannot be neglected in qualitative analysis. It, therefore, becomes necessary to avoid the use of excessive volumes of ether and to wash the ether extracts for the recovery of iridium. The washing must be saved, and not be discarded as directed by Noyes and Bray. Fortunately, the scheme of these authors removes a large amount of the molybdenum together with the tungsten group and not much ether is required for the extraction of the rest of the molybdenum in the tellurium group. The metals of the copper group are separated from iridium and rhodium by precipitation as hydroxides. Whenever the precipitate is voluminous, double precipitation becomes necessary for the quantitative collection of the two platinum metals in the filtrate. Iridium and rhodium are finally precipitated as dioxides. For this purpose it was considered advisable to use a procedure resulting from a combination of the modified methods of Noyes and Bray (17) and of GilChrist (12). These authors use bromine and sodium carbonate-or bromate and bicarbonate-for the simultaneous
A milligram procedure is presented for the analysis of the tellurium and copper groups of A. A. Noyes and W. C. Bray. The scheme provides for the isolation, estimation, and confirmation of 10 micrograms of any member of the groups in the presence of 500 micrograms of any other member. The essential features of the scheme of Noyes and Bray are retained. Rhodium is precipitated by titanous chloride as metallic rhodium, redissolved, and confirmed by the red coloration obtained with stannous chloride. Molybdenum is identified by the blue coloration of the residue of the ether extract, the red coloration produced by potassium thiocyanate, and the precipitation of the black sulfide. The presence of other elcments of the t w o groups is codrmed by slide tests. Examples show the applicability of the procedure.
I
N T H I S study of the tellurium and copper groups, the
scheme of Noyes and Bray (17) has been adopted as in previous investigations (1-5, 7 , 8). Several changes were made, however, to render the procedure more suitable for the handling of small quantities of material. The working technique employed was that developed by Emich as described by Benedetti-Pichler and Spikes (6). Rachele’s pressure cap for microcones (3) was used for heating under pressure. The precipitation of the combined tellurium and copper groups is performed by heating under pressure with hydrogen sulfide. If iridium or molybdenum is suspected, the centrifugate from the hydrogen sulfide precipitate is evaporated to a small volume, made approximately 4 molar in hydrochloric acid, saturated with hydrogen sulfide, and again heated under pressure. This treatment is necessary for a sufficiently complete precipitation of the sulfides of iridium and molybdenum. The analysis of the tellurium group, comprising tellurium, molybdenum, iridium, and rhodium, requires the exercise of special care to assure satisfactory recoveries of the two last-named metals. First, any selenium which might still be present is removed by saturating the strongly acid solution with sulfur dioxide. The solution is then made approximately 2.7 molar in hydrochloric acid for the precipitation 294
ANALYTICAL EDITION
MAY 15.1939
precipitation of the dioxides of the platinum metals. It was found, however, that bromate is not well suited for the pr+ cipitation of iridium while the use of bromine diminishes the delicacy of the precipitation of rhodium. Therefore, the two methods were combined so as first t o precipitate the rhodium by bromate and bicarbonate. iridium is precipitated with the rhodium; the balance of the iridium is then precipitated in the filtrate by adding bromine and sufficient sodium carbonate to maintain a pH of approximately 7.5. men working with large quantities, the separation of black ammonium chloroiridate is sufficient proof of the presence of iridium. An additional confirmatory test appeared desirable for work on a micro scale, and the test described by Cole (9)was adopted. The octahedra and obtained with hexamethylenetetramine are reddish brown and not colorless, as might be inferred from the table of Mitchell (16); however, sometimes the crystals become colorless on standing. This be caused by a process Of reduction as the reddish b ~ octahedra ~ n rapidly undergo the same change when exposed t o sulfur dioxide. The precipitate is also described by Geilmann, and crystals are shown on plate 39 of his atlas (11). For isolation and estimation, rhodium is precipitated as the metal by addition of titanous chloride (go). This procedure appeared more efficient than the precipitation of chloropentammino rhodium chloride, The solution of the metallic rhodium for the subsequent confirmatory test is Performed b y heating under Pressure with hYdrochloric acid and chlorine. T h e treatment with sulfuric and nitric acids on a hot plate, as recommended by Gilchrist (la), is not practical when working in a microcone. The rhodium is confirmed by the addition of stannous chloride and heating (14). The intensity of the red coloration obtained is obviously dependent upon t h e quantity of rhodium. The method of Gilchrist for the separation of rhodium and iridium, Consisting Of precipitation Of metallic rhodium by titanous chloride, removal of the excess reagent with cupferran, and precipitation of iridium dioxide with bromate and bicarbonate, presents various difficulties when applied on a small scale.
some
Isolation of Tellurium and Molybdenum Evaporate filtrateF61 from thallium group to dryness; dissolve residue in hydrochloric acid and treat solution with H ~ S Precipitate P71:
Filtrate F71:
295
PRECIPITATION WITH HYDROGEN SULFIDE. Filtrate F61 from the bromides of the thallium group is treated with 3 cu. mm. of 3 molar ammonium chloride solution and then evaporated to dryness on a stem bath. Tothe residue are added 15 cu. mm. of 2 M hydrochlorio acid and 15 cu. m. of water. The mixture is warmed to hasten solution, and saturated with hydrogen sulfide while warm. After addition Of 70 cu. mm. of water, the mixture is again saturated with hydrogen sulfide, and then heated under pressure for 15 minutes in a bath. After cooling, the mixture is centrifuged, the supernatant solution is saturated with hydrogen sulfide, and then the heating under pressure in the steam bath is continued for 10 minutes. Solution and precipitate are finally separated with the use of a centrifuge. Precipitate p71 is washed with 10 cu. mm. of hot water, and the washing is added to centrifugate 1371, If iridium or molybdenum is expected to be present, centrifugate F71 is evaPC)rakd to approximately 10 CU- mm., treated With 20 ou*mm. of 6 M hydrochloric acid, heated On a steam bath for 10 minutes, saturated with hydrogen sulfide, and heated under pressure in a boiling water bath for one-half hour. After cooling, the solution is saturated again with hydrogen sulfide, and heated for another half hour under Pressure in the steam bath. If any recipitate P71a is obtained, the mixture is cooled and centriaged, the supernatant liquid is removed, and the precipitate is washed with 5 to 10 cu. mm. of hot water. The washings are rejected. Centrifugate F71a contains the cations of the subsequent groups. SOLUTIONOF SULFIDESAND ISOLATION AND ESTIMATION OF TELLURIUM. Precipitate p71 is treated with 2o to 4o cu. mm. of 12 M hydrochloric acid, and the mixture is heated on a steam bath for 5 minutes. Then 4 to 8 cu. mm. of 16 M nitric acid are added, and the mixture is heated a t 70°C. until the precipitate is
d i ~ ~ ~ ~ ~ ; c i pp71a i t a has t e been obtained, it is treated with to 10 cu. mm. of 12 M hydrochloric acid and heated on the steam bath for 5 minutes. Then 1to 2 cu. mm. of 16 M nitric acid are added and the mixture is warmed at 70" c. until the precipitate is dissolved. The solution is transferred to the solution of P71, and two 10-cu mm. portions of 12 M hydrochloric acid are used to make the trinsfer quantitative. The solution of precipitate P71, or the combined solutions of P71 and P71a, are evaporated to dryness on a steam bath. The residue iS dissolved in 10 to 20 CU. mm. O f 12 M hydrochloric acid and the solution is saturated with sulfur dioxide. Any selenium which remained behind from the distillation of the selenium group will precipitate a t this time, and be removed from the solution. For the precipitation of the tellurium, the solution is then diluted with such a volume of water-35 to 70 cu. mm.-as to make the mixture approximately 2.7 molar in hydrochloric acid. The mixture is then saturated with sulfur dioxide and heated under pressure in a steam bath for 15 minutes. After centrifuging, supernatant liquid F72 is transferred to another microcone while still hot. Precipitate P72 is washed with two 10-cu. mm. portions of hot water and the washings are added to filtrate F72. The volume of the tellurium precipitate is compared with that of a precipitate obtained from a tellurium solution of known content. CONFIRMATORY TESTFOR TELLURIUM. Precipitate P72 is heated with 5 to 10 cu. mm. of aqua regia; the resulting mixture is centrifuged, and the clear solution transferred to a slide and
Combine solutions of P71 and P71a
Precipitate P72: Te Dissolve in aqua re ia and treat with Cs8l
Filtrate F72: Evaporate to dryness. Extract residue with ether
Identify by conversion to
KsMo[CNS)a
I
MOSS
Ir, Rh, Pb, Bi, Cu, and Cd
After cooling, 5 cu. mm. of 6 M hydrochloric acid are added to the residue, and the resulting solution is extracted with three portions of approximately 50 cu. mm. of ethyl ether. The ether extracts are collected in a centrifuge cone and washed once with 5 cu. mm. of 6 M hydrochloric acid. The washing, which may contain kidium, is added to aqueous solution S73. IDENTIFICATION OF MOLYBDENUM. Washed ether extract E73 is eva orated in the centrifuge cone to dryness. The residue is heated \y slowly drawing the point of the cone through a Bunsen flame. The appearance of a blue coloration in the point of the cone indicates the presence of molybdenum. Sometimes, however, this blue coloration fails to appear. I n such instances, the coloration will usually appear if the residue is treated with 2 cu. mm. of 6 M hydrochloric acid, the acid evaporated, and the residue heated again.
INDUSTRIAL AND ENGINEERING CHEMISTRY
296
Whatever the result of the foregoing test, the residue is finally dissolved in 2 cu. mm. of 6 M hydrochloric acid, and then 12 M ammonia is added until the solution becomes ammoniacaa. The mixture is stirred and centrifuged. If a precipitate of ferric hydroxide has been obtained, the supernatant solution is transferred to another cone, the precipitate of ferric hydroxide is washed with 5 cu. mm. of 6 M .ammonia,, and the washing is combined with the clear ammoniacal solutlon, which is heated on a steam bath to remove most of the ammonia. Finally the solution is made just acid by adding small portions of 6 M hydrochloric acid. Now 2 cu. mm. more of the acid, 5 cu. mm. of water, and 5 cu. mm. of 1 M potassium thiocyanate solution are added. I n the presence of molybdenum the solution becomes yellow. The mixture is stirred after adding a kernel of metallic zinc of about 0.1-cu. mm. volume. When the stirring is continued for 1 to 2 minutes, the appearance of a cherry-red coloration confirms the presence of molybdenum. The coloration fades in a few minutes and is not suited for estimation of the quantity of molybdenum. ESTIMATION OF MOLYBDENUM. The solution is separated from the metallic zinc, the metal is washed with 5 cu. mm. of water, and the washing is combined with the solution. The latter is treated with 1 cu. mm. of 12 M hydrochloric acid, saturated with hydrogen sulfide, and heated under pressure in the steam bath for 10 to 20 minutes. The volume of the precipitate of molybdenum sulfide is compared with that of a precipitate obtained from a known quantity of molybdenum.
VOL. 11, NO. 5
forms, it is collected with the use of the centrifuge and combined with precipitate P75. If precipitate P75 is voluminous, it is dissolved in approximately 10 to 15 cu. mm. of 12 M hydrochloric acid, and the solution is eva orated to dryness. The residue is treated with 1 cu. mm. of 6 acetic acid, 10 cu. mm. of water, and 3 cu. mm. of 3 M sodium nitrite solution, and the mixture is precipitated with 3 M sodium hydroxide as described above. The centrifugate now obtained is added to filtrate F75, and the precipitate is considered as P75. PRECIPITATION OF DIOXIDES OF IRIDIUM AND RHODIUM. Filtrate F75 is treated with 5 cu. mm. of 12 M hydrochloric acid and evaporated just to dryness. The residue is dissolved by adding 15 cu. mm. of water and heating on a steam bath for 5 minutes. Then 20 cu. mm. of 10 per cent sodium bromate solution are added, and sufficient filtered 1 M sodium bicarbonate solution to render the mixture alkaline. The mixture is then heated on a steam bath for 20 minutes. The separation of a green precipitate indicates the presence of rhodium. The contents of the microcone are centrifuged, and the supernatant clear solution is transferred to another cone. The precipitate is washed with 10 cu. mm. of hot water, and the washing is added to the centrifugate. A minute drop of bromine is added to filtrate F76. The reaction of the mixture is tested by means of nitraeine paper, and the pH is adjusted to approximately 7.5 by the addition of 1 M sodium bicarbonate solution. The mixture is then heated on the steam bath for 20 to 30 minutes. A bluish black precipitate indicates the presence of iridium. Precipitate P76a and the Isolation of Rhodium and Iridium solution are separated, and the latter is rejected. The precipitate is washed with 5 cu. mm. of hot water. Treat solution S73, which contains Ir, Rh, ISOLATION AND ESTIMATION OF IRIDIUM. Precipitates P76 Pb. Bi, Cu. and Cd, with NaNOz and NaOH and P76a, the first mainly consisting of rhodium dioxide and the second mainly of iridium dioxide, are combined as follows: Precipitate P76a is dissolved in a mixture of 6 cu. mm. of 12 M Prwinit,n.t,e ~ 5 % : Fifirate F75 - .-. hydrochloric acid and 2 cu. mm. of 16 M nitric acid. The Ir(N0~)6--- and Rh(N02h--Hydroxides of Pb, Bi, Cu, solution is transferred to precipitate P76, and the mixture is and Cd Add HCl and evaporate to dryness; warmed until P76 has completely dissolved. The cone which dissolve the residue in water and contained P76a is rinsed with two &cu. mm. portions of a mixture heat with NaHCOa and NaBrOa of three volumes of 12 M hydrochloric acid and one volume of 16 M nitric acid, and the washings are added to the solution of the combined precipitates. The solution of the combined precipitates P76 and P76a is Filtrate F76: evaporated to dryness on a steam bath, the residue is treated NaHCOs Brz with 1 to 2 cu. mm. of 6 M hydrochloric acid, and the mixture / \ again evaporated to dryness. The residue is dissolved in apPrecinitate F76a: Filtrate : proximately 1 cu. mm. of 6 M hydrochloric acid and 3 to 5 IrOz Reject cu. mm. of water. The solution is saturated with chlorine and warmed at 50" C. for 5 minutes. Solid ammonium chloride is Combine precipitates P76 and P76a, dissolve then added until the solution appears saturated with this salt. in aqua regia, and treat solution with C12 and A large excess-more than one or two crystals-of solid ammo"821 nium chloride must be avoided. The mixture is heated on the steam bath for 15 minutes, allowed to cool, again saturated with Filtrate F77: chlorine, and allowed to stand for 0.5 hour. Any ammonium Preci itate P77: chloride, which may have separated out, is now dissolved by Tic!& (NH$pcle adding water in cubic millimeter portions, and the black precipitate of ammonium chloroiridate is collected in the point of Precipiiate P78: the cone by means of the centrifuge. Centrifugate F77 is transRh Hexamethylenetetramine ferred to another cone, and the precipitate is washed with 5 Dissolve in HCl and Clz, salt cu. nim. of 3 M ammonium chloride solution. The washing SnClz is added to filtrate F77. The volume of precipitate P77 is I compared with that of ammonium chloroiridate obtained with Red coloration a known amount of iridium. CONFIRMATORY TESTFOR IRIDIUM. Precipitate P77 is disSEPARATION OF COPPERGROUPFROM IRIDIUM AND RHODIUM. solved in 5 to 10 cu. mm. of water, warming if necessary; a drop of the solution is transferred to a microscope slide and treated Solution 573 is first warmed to remove the dissolved ether, and with a kernel of hexamethylenetetramine of approximately 0.1then evaporated just to dryness on the steam bath. The residue1 cu. mm. volume. The separation of reddish brown octahedra is dissolved in 1 cu. mm. of 6 M acetic acid and 10 cu. mm. of and crosses confirms the presence of iridium. water; the soIution is treated with 5 cu. mm. of 3 M sodium ISOLATION AND ESTIMATION OF RHODIUM. Filtrate F77 is nitrite solution and warmed a t 60" to 70" C. for 5 minutes. evaporated to dryness, and the residue is treated with 2 cu. mm. After cooling, and without filtering, 1-cu. mm. portions of 3 M of 18 M sulfuric acid and 40 cu. mm. of water. The mixture sodium hydroxide solution are added with stirring until the is heated on the steam bath for 5 minutes, after which a very mixture is alkaline to litmus paper. If the hydroxide preslight excess of a 15 per cent solution of titanous chloride is cipitate is voluminous the mixture may be diluted with 10 to added, and the heating on the steam bath is continued for 1 to 20 cu. mm. of water during neutralization. After centrifuging, 2 minutes. A precipitate of black metallic rhodium is collected precipitate and solution are separated, and the precipitate is in the point of the cone, and the supernatant solution is removed washed with 5 to 10 cu. mm. of hot water; the washidg is added at once and rejected. Precipitate P78 is washed with 10 cu. mm. to the centrifugate. Filtrate F75 is finally treated with 5 of 0.4 M sulfuric acid, and the volume of the precipitate is comcu. mm. of 1 M sodium bicarbonate solution, and, if a precipitate pared with that of a known quantity of metallic rhodium similarly precipitated. 1 A blue coloration of this residue indicates inoomplete separation of the CONFIRMATORY TEST FOR RHODIUM. Precipitate P78 is molybdenum. It is then necessary t o repeat the extraction with ether 88 treated with 15 to 30 cu. mm. of 12 M hydrochloric acid. The described above. Since modt of the molybdenum is removed with the mixture is saturated with chlorine, and, if necessary, heated tungsten group and the small quantities found in the tellurium group are under pressure on a steam bath until the precipitate is dissolved. readily extracted by ether, molybdenum will rarely be present a t this stage If complete solution is not obtained after heating for several of the analysis.
+
+
/ -\ +
I
+
%
ANALYTICAL EDITION
MAY 15, 1939
minutes, the supernatant solution is removed from the metal and transferred to'another cone. The residue is treated with another portion of 15 to 30 cu. mm. of 12 M hydrochloric acid, and the treatment with chlorine and the heating under pressure are repeated as described above. The resulting solutions of rhodium are combined and freed by centrifuging from any white precipitate which may appear a t this stage whenever too large an excess of titanous chloride is used in the precipitation of the metallic rhodium. The clear solution of rhodium is evaporated to a volume of approximately 5 cu. mm. and then taken up into a capillary. The cone used in the concentration of the rhodium solution is rinsed with 3 to 5 cu. mm. of stannous chloride reagent, which is then also taken up into the capillary. The capillary is sealed at both ends, its contents are mixed, and the capillary is finally placed for 5 minutes in boiling water. The appearance of a yellowish red to deep red coloration in the capillary confirms the presence of rhodium.
297
usually recognized by the blue coloration of the ammoniacal solution, and the estimation of co per is based on the colorimetric evaluation of the intensity ofthe coloration. If a further confirmatory test for copper is desired, one fourth of filtrate F82 is taken up with a capillary tube and treated with 1 cu. mm. of 6 M acetic acid and 1 to 2 cu. mm. of 0.25 M potassium ferrocyanide. The capillary is sealed a t both ends and its contents are mixed by centrifuging and then allowed to stand for 2 to 3 minutes. The reddish brown precipitate of cupric ferrocyanide can then be collected a t one end of the capillary by means of the centrifuge. The clear solution may be removed, and the precipitate washed with 5 cu. mm. of hot water and dissolved in 5 to 10 cu. mm. of 6 M nitric acid. Transference of this solution to a slide, evaporation to dryness, solution of the residue in 2 M nitric acid, and treatment with potassium-mercuric thiocyanate furnish the characteristic crystals of copper-mercuric thiocyanate.
Analysis of the Copper Group Dissolve precipitate P75, which may contain h droxides of Pb, Bi, Cu, and Cd, in HdOa and evaporate with H2S01
/\
/
PrecGitate PSI : PbSOc
b
P b r01
I
K?PbCu(NOz)a
\
Filtrate $81 :
+
3"
/\
Precipitate P82: Bi(OH)3
1 si
Cs3BizI.a
Filtrate F82:
NH3 complex ions of Cu and Cd. Divide solution into two portions. Use one fourth for estimation and confirmation of Cu, three fourths for estimation and confirmation of Cd
ISOLATION AND ESTIMATIOX OF LEAD. Precipitate P75 of the hydroxides of the copper group is dissolved in 5 to 10 cu. mm. of 16 M nitric acid. To the clear solution are added 3 cu. mm. of 18 M sulfuric acid, and the mixture is evaporated on the steam bath to a volume of approximately 3 cu. mm. This evaporation, which is carried out to eliminate the nitric acid, is accomplished rapidly by blowing air through the cone. After cooling, the residue is diluted with 10 cu. mm. of water, and the mixture is cooled and then allowed to stand for 3 minutes. The contents of the cone are centrifuged, and the volume of precipitate P81 is compared with that of a lead sulfate precipitate obtained from a known quantity of lead. Centrifugate F81 is transferred to another cone; the precipitate is washed first with 3 to 5 cu. mm. of 2 M sulfuric acid and then with 3 to 5 cu. mm. of cold water. The washings are added to centrifugate F81. CONFIRMATORY TESTFOR LEAD. Precipitate P81 of lead sulfate is either used for a triple nitrite test (S), or is dissolved in 5 to 10 cu. mm. of 3 M ammonium acetate solution, warming if necessary, and precipitated by the addition of 1 cu. mm. of a 1.5 M solution of potassium chromate. The precipitation of the lead chromate may be performed in a capillary, or in a cone with cylindrical tip (8), and the volume of the lead chromate may be used for the estimation of the quantity of lead. It is finally possible to subject the chromate precipitate to the triple nitrite test. ISOLATION, CONFIRMATION, AND ESTIMATION OF BISMUTH. Filtrate F81 from the lead sulfate is made distinctly ammoniacal by the addition of 20 cu. mm. of 6 M ammonia. The mixture is centrifuged, the supernatant solution transferred to another cone, and the precipitate washed with 5 cu. mm. of hot water. The washing is added to centrifugate F82. Precipitate P82 of bismuth hydroxide is treated with 5 to 10 cu. mm. of freshly prepared (6) sodium stannite reagent, and the contents of the cone are mixed and centrifuged. The volume of the black precipitate of metallic bismuth is used for the estimation of the quantity of this metal. The black precipitate is finally washed with two 10-cu. mm. portions of hot water, abd then dissolved in 5 cu. mm. of 16 M nitric acid. A drop of this solution is transferred to a slide, evaporated to dryness, the residue dissolved in 2 M nitric acid, and this solution used for the precipitation of the cesium iodobismuthite or the bismuth cobalticyanide (6). THE DETECTIONAND ESTIMATION OF COPPERAND CADMIUM has been described in former publications (6). The copper is
Limitations of the Scheme The range of applicability of this scheme of analysis may be seen from Table I, which shows the results obtained in the analyses of solutions of various composition. The quantities recovered represent averages derived from the results of several experiments. All the estimations were performed with the use of microcones with cylindrical tip (8). The compositions of solutions X and Y were unknown t o the analyst. The small amount of lead found in the analysis of X was introduced as a n impurity of the copper salt used in the preparation of solution X.
TABLEI. ANALYSES OF SOLUTIONS OF KNOWNCOMPOSITION Number of
Solution .4nalyses
Composition Found Micrograms
A
B
2 2
C D
12 5
E
3
F
3
G
2
H
4
I
5
J
5
K
1
L
2
X
1
Y
1
100 Te, 140 Mo, 120 Pb
Actual Composition Micrograms 10 of each 10 of each 20 of each 20 of eaoh 10 of each 10 of each 10 of each 20 of each 10 of each 50 of each 10 of each 100 of each 10 of each 150 of each 10 of each 200 of each 10 of each 500 of each 150 of each 10 of each 100 IC, 200 Rh, 1 Pb, 200 Cu 100 Te, 200 Mo, 200 Pb
The various limiting proportions have not been determined in the exact sense. However, no difficulties were experienced in detecting 10 micrograms of any element in the presence of 500 micrograms of any other element of the copper and tellurium groups.
Acknowledgment The authors are indebted to the authorities of the Brooklyn College of Pharmacy for permission to use their laboratory facilities.
Literature Cited (1) Benedetti-Pichler, A. A., and Bryant, J. T.,IND. ENQ.CHEM., Anal. Ed., 10,107 (1938). (2) Benedetti-Pichler, A. A , , Crowell, W. R., and Donahoe, C., 11, 117 (1939). (3) Benedetti-Pichler, A. A., and Rachele, J. R., Ibid., 9, 589
rw.,
(1937). (4) Benedetti-Pichler, A. A., and Rachele, J. R., Mikrochemie, 19,
Douglaston, N. Y . , Microchemical SerGice, 1935.
VOL. 11, NO. 5
INDUSTRIAL AND ENGINEERING CHEMISTRY
298
(15) McAlpine, R. X.,and Soule, B. A., “Qualitative Chemical Analysis”, p. 287, New York, D. Van Nostrand Cb., 1933. (16) Mitchell, C. A., “Recent Advances in Analytical Chemistry, Vol. 11, Inorganic Chemistry”, p. 334, Philadelphia, P. Blakiston’s Son & Co., 1931. (17) Noyes, A. A., and Bray, W. C., “Qualitative Analysis for the Rare Elements”, New York, Macmillan Co., 1927.’ (18) Scott, W. W.,”Standard Methods of Chemical Analysis”, 4th ed., p. 388, New York, D.Van Nostrand Co., 1929. (19) Short, M. N., U. S. Geol. Survey, Bull. 825, 165 (1931). (20) Wada, I., and Nakazona, T., Sei. Papers Inst. Phys. Chem. Research (Tokyo), 1, 139 (1923).
(7) Benedetti-Pichler, A. A., and Spikes, W. F., Mikrochemie, 19, 239 (1936). (8) Benedetti-Pichler, A. A., and Spikes, W. F., Ibid., Molisch Festschrift, 3 (1936). (9) Cole, H. I., Philippin,; J . Sci., 22, 631 (1923). (10) Fresenius, W. T., Introduction to Qualitative Chemical Analysis”, p. 37, New York, John Wiley & Sons, 1921. (11) Geilmann, W.,“Bilder our qualitativen Mikroanalyse anorganischer Stoffe”, p. 39, Leipzig, Leopold Voss, 1934. (12) Gilchrist, R., Bur. Standards, J . Research, 9, 547 (1932). (13) Rillebrand, W. F.,and Lundell, G. E. F., “Applied Inorganic Analysis”, p. 107, New York, John Wiley & Sons, 1929. (14) Iwanow, W.N., Chent. Zentr., 4, 135 (1923).
Pregl Sulfur Combustion of Metallic Compounds JOSEPH F. ALICINO, Fordham University, New Yorlr, N. Y.
HE only limitation to the excellent Pregl catalytic cornfor sulfur is its lack of applicability to bustion which contain a (I). As these Occur fiequently, an attempt was made to modify the method to include them. a few preliminary experiments showed that the residue from this type of substance contained a considerable amount of metallic sulfate, attempts were made to prevent its formation or to decompose it when formed. The substitution of a porcelain boat to avoid the catalytic effect of platinum did not prevent its formation, and the addition of various substances, such as potassium dichromate, chromium trioxide, sodium peroxide, and cupric nitrate, to the sample did not leave the residue sulfate-free. As it seemed probable that the formation of sulfate could not be avoided under the conditions of the determination, it was decided that the solution of the problem depended on treatment of the combustion products to obtain the theoretical yield of barium sulfate. While only a comparatively few compounds were readily available, their metals belonged to four of the five qualitative groups and possessed widely different chemical behavior.
T
This treatment ensures the quantitative transfer of sulfate ion with the minimum amount of solvent. In the case of the barium compound, the transfer of the residue to the crucible was accomplished by overturning the boat and spraying vigorously from the wash bottle t o remove the last traces of residue. Other barium compounds, if present, are dissolved by the acid, leaving only the insoIubIe sulfate. Insoluble residues of other metals must be extracted by boiling gently with 0.1 N hydrochloric acid and treating the extract with barium &loride in the usual manner, Chromium residues contain no sulfate (Table I), and subsequent treatment of the residue is unnecessary. TABLE11. YIELDOF BARIVMSVLFATE (Separate treatment of residue omitted) BaSO4 Sulfur Sample Found Calcd. Found Calcd. Me. Mg. Mg. % % Lithium cystinate 5.324 9.81 9.85 25.32 25.40 Compound
Barium co per cystinate cystinate So$iumj3-na hthoquinone suyfonrtte
Me. Lithium cystinate. C~HioO4N~,BLi, Bariumoystinate CsHioOiNzSiBa) Reinecke salt, C~HIONISIC~ Co per cystinate, &HIoO~N&CU Sodium8-naphthoquinonesulfonate, CioHsOsSNa
.
6.695 5.545 6.087 6.872 4.356 4.542 5.503 4.552 6.705 7.333
Sulfur .7
Found
Cdcd.
25.40
%
Mg.
Me.
Mg.
%
6.02 4.99 3.17 3.61
48.75 48.87 42.27 42.47
1:58 1.31 3.14 3.44
18:65 18.71 52.21 52.36
6.33 5.22 4.33 4.89 12.12 12.62 6.89 5.69 2.86 3.13
12.35 10.21 7.50 5.50 12.12 12.62 8.47 7.00 6.00 6.57
12.38 10.25 7.55 8.52 12.09 12.60 8.50 7.03 6.01 6.57
26.34 25.29 16.92 16.98 38.22 38.16 21.14 21.12 12.29 12.31
Mu.
..
...
7.49 7.25 6.19
21,15 16.98 12.29
21.21 17.04 12.31
Discussion
TABLE I. YIELDOF BARIUMSVLFATE
Compound
7.22 8,47 6.17
I
* (Reaidue and contents of spiral treated separately) YBaSOdFrom Total Bas04 Sample From residue spiral Found Calcd.
5.500 5.840 6.904
%
and treated with barium
17.04 38.11 21.21 12.31
The residue and the contents of the spiral were treated separately, as shown in Table I, to show the yields of barium sulfate. Table I1 shows the results when the separate treatment of the residue is omitted. The acid-soluble residues are placed in the weighed and dissolved by means of the acid washings of the spiral contents. The total sulfate is collected
-
in the
fashion. When insoluble residues other than barium are formed, the hydrochloric acid extract can be added to the partly evaporated contents of the spiral previously placed in the weighed crucible. I n this manner accurate results can be obtained.
Acknowledgment Experimental The substances were run according to pregys method (8, 31, (4). The contents of the spiral were treated in the usual manner and the weights of barium sulfate recorded. The residues left in the boat were weighed, but, owin t o the variable amounts of sulfur and metal present in the Sam&, did not conform to the weight demanded by the pure sulfate. This indicated that the oxide or carbonate was formed in addition to the sulfate, and the weights were therefore disregarded as of no significance. The acid-soluble residues, which included all but the barium derivative, were transferred t o another weighed crucible and dissolved in 7 to 10 ml. of 0.1 N hydrochloric acid, and the boat was rinsed with hydrochloric acid (1 t o 200) from a wash bottle. as modified by Saschek
The author is indebted to G. Toennies of the Lankenau Hospital, Philadelphia, for the lithium and barium salts used in this work.
Literature Cited (1) Niederl and Niederl, “Organic Quantitative Microanalysis”, pp. 141-53, New York, John Wiley & Sons, 1938. (2) Pregl, F., “Die quantitative organische Mikroanalyse”, 3rd ed., pp. 131-65, Berlin, JuIius Springer, 1930. (3) Roth, H., and Daw, E. B., “Quantitative Organic Microanalysis of Fritz Pregl”, pp. 116-28, Philadelphia, P. Blakiston’s Son BC Co., 1937. (4) Saschek, W., IND. ENQ.CHEM.,Anal. Ed., 9, 491 (1937).
