A QUALITATIVE PROCEDURE for the ANALYSIS of' GROUP I1 J. L. MAYNARD, H. H. BARBER
AND
M. C. SNEED
University of Minnesota, Minneapolis, Minnesota
QUALITATIVE scheme of analysis of Group I1 is presented in three parts. Part I contains a discussion of the separation of Group I1 into Divisions A and B by a special sodium hydrogen sulfide reagent. The solubilities of the sulfides in the reagent are given. Part I1 gives the analysis of Division A. This Division contains the ions of lead, bismuth, copper, cadmium, part of the gold, and the platinum metals. In Part I11 is given the analysis of Division B. The ions of this Division are those of mercury, arsenic, antimony, tin, gold, molybdenum, selenium, and tellurium. Because of its rareness, germanium, the only other element of Group 11, is omitted.
A
dissolve stannous sulfide very readily. The composition of the reagent was changed so that to each liter of a 3 N solution of sodium hydroxide saturated with hydrogen sulfide there was added 4 g. of sulfur and 3.5 g. of sodium hydroxide. The sulfur accomplished the oxidation of stannous sulfide to the stannic form and the more strongly acid nature of the latter resulted in the ready solution of this compound in the reagent. As for the solubility of bismuth sulfide in the reagent, it was found that as an average of nine determinations only 2.5 mg. of the sulfide out of 0.2676 g. was dissolved after boiling for two hours with 100 ml. of the reagent (5). Only about 0.1 mg. of bismuth is dissolved when 0.2 g. of its sulfide is digested for five minutes with 20 ml. of the reagent. PART I The modified sodium hydrogen -sulfide reagent has been used by classes in qualitative analysis at the SEPARATION OF GROUP I1 INTO DIVISIONS A AND B* University of Minnesota since 1919, and the complete procedure as finally adopted is to be found in "Revised Group I1 in qualitative analysis is generally conProcedures for Qualitative Chemical Analysis" (6). sidered to contain those metals whose sulfides are pre- The sulfides of mercury (ic), arsenic, antimony, and cipitated by hydrogen sulfide in acid solution. The stannic tin are completely soluble in the special reagent, ions of the commonly occurring metals found in this while those of lead, copper, cadmium, and bismuth are group are those of mercury (ic), arsenic, antimony, tin, very difficultly soluble. These latter elements conlead, copper, cadmium, and bismuth. Many schemes stitute Division A of the Sneed procedure. of analysis effect a preliminary separation of the sulIn addition to the eight commonly occurring elements fides of this group into two sub-groups by means of whose sulfides are precipitated by hydrogen sulfide in yellow ammonium sulfide. Treatment of the metallic acid solution there are eleven other elements that fall sulfides with this reagent yields soluble complex thio in this group and, if present in solution, would be precompounds of arsenic, antimony, and tin. The sulfides cipitated as sulfides in Group I1 of the qualitative proof the other metals of this group remain undissolved. cedure. The latter elements are gold, selenium, telHowever, the use of any reagent containing ammonium lurium, molybdenum, platinum, palladium, osmium, polysulfide involves the analyst in a number of diruthenium, rhodium, iridium, and germanium. It culties (1). A. A. Noyes (2) separates the sulfides of became of interest to us to incorporate these elements, Group I1 into two divisions by the use of a reagent with exception of the extremely rare germanium, in the containing sodium hydroxide, sulfide and polysulfide. analytical procedure used for the identification of the This reagent has the same disadvantages as yellow eight commonly occurring elements, and to modify or ammonium sulfide because i t contains too much poly- elaborate the scheme to make it all inclusive. sulfide. Furthermore, the reagent dissolves appreciable Since the key reagent of the procedure for Group I1 amounts of bismuth and copper sulfides. is the sodium hydrogen sulfide reagent, it became necesWith a view toward the elimination of some of these sary to establish its behavior with each of the sulfides of difficulties, Sneed (3) introduced a new reagent to take the ten metals it was desired to add to the scheme of the place of yellow ammonium sulfide. The original analysis. Hilger (7) found the sulfides of tellurium and reagent was a solution of sodium hydrogen sulfide, but selenium to be completely soluble in the reagent, while modification was necessary because it dissolved apprecipalladium sulfide remained undissolved. Weber (8) able auantities of bismuth sulfide (.4.) and failed to established the insolubility of iridium sulfide in the * An abstract of a portion of a thesis submitted to the Faculty special reagent and Barber (9) found platinum sulfide of the Graduate School of the University of Minnesota by H. H. Barber in partial fulfilment of the requirements for the degree to be very slightly soluble. Experimental work by Maynard and Sneed shows that the sulfides of osmium, of Doctor of Philosophy, June 1926.
ruthenium, and rhodium are very difficultly soluble in the sodium hydrogen sulfide reagent. The sulfides of the two remaining elements, molybdenum and gold, are known to be completely soluble in solutions of alkali sulfides. In order to separate Group I1 into the two subgroups the sulfides are digested for five minutes with 40 ml. of the sodium hydrogen sulfide reagent. By this treatment the sulfides of arsenic, antimony, selenium, tellurium, gold, and molybdenum are readily dissolved by the reagent. Stannous tin, as previously mentioned, must he oxidized to the stannic state by the polysulfide before solution takes place. Mercuric sulfide is almost insoluhle in the cold reagent but it dissolves upon heating according to the equation:
The solubility of the sulfides of Division A in the reagent was carefully checked by two methods. In all cases 40 ml. of the reagent was used and the time of digestion of the sulfides with the sodium hydrogen sulfide was five minutes. In the first method the sulfides of the platinum metals and those of the base metals were treated separately with the reagent. Only 0.5 mg. of each metal was used for each test. In every instance enough sulfide remained undissolved to give a good test for the metal. In these tests i t was observed that the sulfides of copper, iridium, and bismuth, as well as some of the others, dissolve in appreciable amounts in the cold reagent but precipitate upon digestion. In the second method the sulfides were digested separately as before, but the amount of metal present in each instance was increased tenfold. This time the filtrates from the undissolved sulfides were tested for the corresponding metal. No tests were obtained for lead, cadmium, palladium, ruthenium, rhodium, and iridium. Osmium and platinum gave indications of mere traces. Both copper and bismuth sulfides dissolved in sufficient amounts to give tests for these metals. However, the amount of each of these was small. Bismuth was found by the cinchonine-potassium iodide test while sodium diethyldithiocarhamate was used to test for copper. The ferrocyanide test for copper was inconclusive. Several factors (10) seem to influence the solubility of bismuth sulfide in the reagent. In all tests, even when only 0.5 mg. of bismuth was present, the greatest part of the Bi& remained undissolved. In the account just given regarding the solubility of sulfides, it is seen that the platinum group elements, all of whose sulfides are insoluhle in the special reagent, fall in the same suh-group with copper, cadmium, bismuth, and lead. Any metallic gold formed by reduction with hydrogen sulfide when the Group I1 precipitation is made will also amear with the vrecedine metals. The main portion b'f the gold, togeiher with selenium, tellurium, and molybdenum, belongs in the sub-group with arsenic, antimony, tin, and mercury.
PROCEDURE FOR THE ANALYSIS OF GROUP I1
PrecipPtation of the Su&des.*-The solution should contain not less than 1 or more than 50 mg. of each of the metals. In the experimental work the following compounds were used: HzSe03, NazTeOa, AuCb, (NH&Mo04, SbC4, NazHAsOa, SnC14,HgCh, HzPtCla, PdClz, RuC5, OsOr, IrC13, RhC4, CuC12, CdC12,BiC13, and Pb(NO&. The solution to be tested should have a volume of 60 ml. and must be 6 N with respect to hydrochloric acid. It should be heated to 90' and treated with a fairly rapid stream of H2S for three hours. At the end of this time the volume measures ahont 30 ml. This solution should he diluted to six times its volume and then treated with H,S for fifteen minutes a t a temperature of 90'. The precipitate is removed by filtration and washed with H B water. Evaporate the 6ltrate to a volume of 5-7 ml., add an equal volume of water and then pass in H2Sfor twenty minutes a t a temperature of 90". The solution is now diluted to eighteen times the original volume of from 5 to 7 ml. and H2S is passed in for ten minutes. Filter and then wash the precipitate with HzS water. Reject the filtrate unless other groups are present. Separation of the Su&des by means of the NaHS Reagent.-Combine the precipitates obtained above and digest for five minutes with 40 ml. of the special reagent. Filter, wash the residue with one per cent. NaOH solution and then with a one per cent. solution of NH4N03 saturated' with H&. Remaining undissolved in the special reagent are the sulfides of Cu, Cd, Bi, Pb, Pt, Pd, Rh, Ru, Ir, Os, andsmall amounts of metallic gold. Dissolved in the special reagent are the complex thio salts of Sb, Hg, As, Sn, Se, Te, Ma, and Au. DISCUSSION OF THE PROCEDURE
During the development of this procedure the authors have kept in mind certain requirements necessary to a scheme of analysis that is to be suitable for classroom use. It is believed that students who have had a first course in qualitative analysis in college will have acquired a sufficient knowledge of the chemistry of the commonly occurring elements so that no difficulty will he encountered in the separation and identification of these elements. Additional study will, of course, he necessary before carrying out those parts of the procedure dealing with selenium, tellurium, molyhdenum, gold, and the platinum metals. All of the special reagents required, aside from the substance used in the detection of platinum, are widely used in modem courses in qualitative analysis. The use of dimethylphenylbenzylammonium chloride is original with one of us, and a more detailed study of the efficiency of the reagent is in progress. The reagent is specific for platinum under the conditions set forth in this procedure and will identify the element in a solu*Abstracted from a thesis presented to the Faculty of the Graduate School of the University of Minnesota by J. L. Maynard in partial fulfilment of the requirements for the degree of Doctor of Philosophy, June 1938.
tion containing as little as 3 gamma of the metal per milliliter. Dimethylphenylbenzylammonium chloride is not available from manufacturers of organic chemicals, but it may be easily prepared by the action of benzyl chloride on dimethylaniline. Details are to be found in a following section dealing with the special reagents used in this procedure. Precipitation of the SulfLdes of Group II.-In order to secure complete precipitation of iridium as sulfide, the temperature of the solution must be near the boiling point, and the treatment with hydrogen sulfide must be continued for a period of several hours in 6 N acid solution (11). Dilution to an acid concentration of 1 N produces a favorable condition for the precipitation of the other sulfides in this group with the exception of molybdenum, cadmium, and lead. After precipitation a t this concentration the directions call for evaporation to a volume of from 5 to 7 millimeters. This small volume of solution will usually be colored blue if ruthenium is present in the original solution. The color is said to be due to ruthenium dichloride (12). I t has been found that further treatment with hydrogen sulfide in 3 N acid solution a t 90' will complete the precipitation of ruthenium, while a fmal precipitation in 0.3 N acid results in the separation of the remaining amounts of lead, cadmium, and molybdenum. It is to be noted that throughout this procedure various operations are carried out a t a temperatwe of 90'. The authors have found it most convenient to use an electric hotplate with a resistance in the line so adjusted as to give the desired temperature. Separation of the Sulfides by Means of the NaHS Reagent.-The efficiency of this reagent in the separation of Group I1 into two sub-groups has been discussed in the introductory portion of this article. It is only necessary to point out that a dense iilter paper or filtering crucible must be used to filter out the very finely divided sulfides of Division A. The dark red color of the filtrate containing thio salts of the elements of Division B makes it difficult to detect the presence of suspended solids that will be present unless a sufficiently retentive filter be used. PART I1 THE ANALYSIS OF DIVISION
A*
any basic changes in the procedure finally selected for the analysis of the platinum metals. The decision to use a scheme for the separation of the platinum metals as the basis for the analysis of the entire sub-group necessitated a critical examination of previously used methods. Those investigated were developed by Deville and Debray (13), Claus (14), Gibbs (15), Bunsen (16), Mylius and Dietz (17), Koukline (IS), Wunder and Thiiringer (19), Mylius and Mazzucchelli (20), Friend (21),Weber (22), Noyes and Bray (23), and Gilchrist and Wichers (24). An examination of each of these procedures showed that only the last-named method met the requirements of a scheme suitable for use in a course in qualitative analysis. Designed to give a precise quantitative separation of the six platinum metals, the GilchristWichers procedure also lends itself to use as an excellent qualitative scheme of analysis. In adapting this procedure for use in the qualitative analysis of Group 11, the present authors have deviated from the quantitative method in only one important respect. Gilchrist and Wichers use titanous chloride to separate rhodium from iridium. When a solution containing the chlorides of these elements is treated with the aforementioned reagent, rhodium is reduced to the metallic state (25). Excess titanium is then removed from the iridium solution by precipitation with cupferron. The expense involved in the use of titanous chloride, together with the sensitiveness of the solution toward oxidation on exposure to air (26),makes it unsuitable for general classroom use. Furthermore, the elimination of excess titanium introduces an additional operation that consumes a considerable amount of time. The method finally adopted by the present authors for the identification of rhodium in the presence of iridium is used by Noyes and Bray (27). This procedure is well adapted to qualitative use and involves no special reagents. In addition to the major change noted in the preceding paragraph, a number of minor deviations from the Gilchrist-Wichers procedure have been made. These involve differences only in the quantities of reagents used. Since the quantitative method did not include confirmatory tests for the platinum metals, these tests have been supplied in the present scheme.
INTRODUCTION
OUTLINE OF A PROCEDURE FOR THE ANALYSIS OF DIVISION A OF GROUP I1
Soon after the present research was undertaken i t became obvious that when osmium, ruthenium, rhodium, and iridium were included in the copper subgroup, the ordinary scheme of analysis would have to be abandoned. The satisfactory solution of the problem was found to lie in the choice of a proven method of analysis of the platinum metals as the basis for the procedure developed in this investigation. Distinctive reactions for the detection of the base metals in this sub-group were so chosen as to make unnecessary
Orizinal Solution H2SeOl, Na2TeOr AuCi, (NH,)sMoOl, NanH.4~0~.SbCla, SnCh HgCL, H2PtCb, PdC4, RuCls, OsO*, IrCIs, RhCls, CuClr, BiC4, CdCL and Pb(NO&. Not less than 1 or more than 50 ma. of eachmetal should be present. Adjust volume to 30 ml. and then add an equal volume of HClt to make 6 N. Heat to 90°, pass Hi3 for three hours. Volume now will be about 30 ml. Dilute to six times this volume and pass in H~Sforfifteenminutes at 90'. Filter, wash precipitate with H d water. Evaporate filtrate to volume of 5 to 7 ml., heat to 90' and pass in H 9 for twenty minutes. Dilute to eighteen times the volume of 5 to 7 ml. and treat with HxS for ten minutes. Filter, wash the precipitate
* An abstract of a portion of a thesis presented to the University of Minnesota by J. L. Maynard.
t Unless otherwise specified, the acids mentioned are the con-
centrated acids ordinarily supplied a reagents.
with HzS water. Combine the precipitates. If Groups 111, IV, and V were present they would be fouxd in the filtrate from t h e last sulfide orecioitate.
Solutioa Division B Thio salts of Se, Te, Au, Mo, As, Sb, Sn, Hg. Directionsfor the analysis of this solution are to be found in Part 111 of this article.
Distillate 0s Evaporate 20 ml. to fumes of HdO,. Dilute to three times the volume. Add several crystals of thiourea. Pink or rose color shows presence of 0s.
Dixtillatc Ru Evaporate a t 90°. Add 5 ml. of HCI. Digest a t 90° far iifteen minutes. Add 15 ml. H,O, then excess strongly ammaniacal 2 M Na&Ol. Boil. Violet color is Ru.
Residue Division A Metallic gold and sulfides of Pt, Pd, Ru, Os, I r,Rh, Cu. Cd, Bi, Ph Dissolve in 20 ml. dilute aqua regia (6 HCI-1 HNO4 HaO). Dilute to 100 ml. Add 40 ml. of 1-1 HNOs. transfer to retort and distill for one hour. Catch distillate in 100 ml. 1-1 HCI kept saturated with SO1. Keep end of delivery tube below surface ol acid throughout distillation. Rcsidue Ru, Pb, Bi, Au, Pd, Cu, Cd, Pt, Ir, Rh. Evaporate to drynessat 90'. Destroy HNOI by evaporation to dryness with HCI. Dissolve residue in 20 ml. HzO and 5 ml. HZSO,. Boil to fumes of HaS04. Add 45 ml. H.0, 50 ml. of ten per cent. aqueous NaBrOa. Distill from retort for one hour into 100 ml. 1-1 KC1 kept saturated with SO2.
Residue Pb, Bi. Au. Pd, Cu, Cd, Pt, Ir, Rh Destroy B a s - by addition of successive 5 ml. portions of HCI. Add 5 ml. excess HCI; evaporate a t 90'. Add 2 ml. HCI, then dilute to a volume of 100 ml. Add 0.5 g. of NadO,. Allow to stand for ten minutes. Filter.
Fdtratc Bi, Au, Pd, Cu, Cd, Pt, I r , Rh Bring up to pH 3 by careful addition of solid NaHCOa. Use cresol red as indicator. Let stand for fifteen minutes. Filter.
Precipitate Pb Dissolve the PbSOl in a hot solution NH40Ac-HOAc (7 ml. 2 N NH,OAc and 3 ml. 6 N HOAc). Add solution of KICrO,. Yellow precipitate shows Pb.
Filtrate Au, Pd, Cu, Cd, Pt, Ir, Rh Add 5 ml. of HC1 and then pass in SOn for fifteen minutes a t 90". Let stand a t 90" for 0.5 hour. Allow the solution to cool and then filter it through a dense filter paper.
Precipdilete Bi Dissolve in 3 ml. 3 N HNOa and then dilute to volume of 18 ml. Drop of solution on filter paper gives orange color with 2 drops of c i n c h m i n t KI reagent if Bi is present.
Fillrats Pd. Cu, Cd, Pt, Ir, Rh Boil until all SO*is expelled. Cool to room temperature and then add 3 ml. of a one
Precipdate Au and traces of Pd Dissolve in dilute aqua regia. Destroy HNO. by evaporation with HCI. Dissolve resi-
per cent. alcoholic solution of dimethylglyoxime. Let stand for 0.5 hour. Yellow predpitate is Pd. Filter.
due in 12 ml. 3 N HCl. Add 2 ml. five per cent. aqueous hydroquinone. Boil five minutes. Precipitate is Au. Filter. To filtrate add 1 ml. one per cent. alc. dimethylglyoxime. Yellow precipitate confirms Pd.
FiItrate Cu, Cd, Pt, Ir, Rh Evaporate until separation of solids causes bumping. Add 3 ml. HNOs and evaporate t o dryness a t 90'. Treat residue with 20 ml. HCI and boil almost to dryness. Repeat this treatment. Evaporate to complete dryness a t 90°. Add 20 ml. HC1. Stir thoroughly and then filter through fritted glass filtering crucible. Wash with hot HCI. Filtratc Cu, Pt, Ir, Rh Evaporate to volume of 10 ml. Add 65 ml. HxO, then saturate with SOn Make barely alkaline with 10 M NaOH and then just acid with HCl. Add 2 ml. of four per cent. aqueous NHCNS saturated with SO2. Allow to stand for one hour. Filter. Filtrate Pt, Ir. Rh Boil down to one-half the volume. Destroy CNS- by addition of HNOa. Evaporate to formation of crystals. Add 15 ml. HCI, digest a t 90" for 5 minutes. Cool, filter off NaCl and wash i t with 5 ml. HCI. Discard the NaCI. Evaporate filtrate to a syrup, dilute t o 100 ml. Boil, add 10 ml. aqueous ten per cent. NaBrOa, then raise pH to 6 with solid NaHCOs. Use brom cresol purple as indicator. Add 5 ml. ten per cent. NaBrOa and boil for five minutes. Add 20 ml. ten per cent. NaHCOs, 5 ml. ten per cent. NaBrOs, boil fifteen minutes. Filter.
Destroy BrOs- with HCI. Boil until solids begin to settle out, then continue to dryness a t 90". Add 20 ml. HCI and bail for three minutes. Filter off solid NaCl Dilute filtrate to 100 ml. Treat 20 ml. of this solution with 5 ml. of ten per cent. aqueous dimethylphenylbenzylarnmonium chloride. Crystalline precipitate shows Pt.
Residue NaCl CdCL Take half the solid. Add just enough H&04 to convert chlorides to sulfates. Bail to dryness. Dissolve residue in H.0 and make ammoniacal. Filter. Pass H2S. Yellow CdS confirms Cd.
+
Dissolve in hot HNOJ. Dilute, flter, then evaporate t o dryness. Dissolve residue in HCI. Dilute. Test separate portions with NH40H and with GFe(CN)s. Blue color and reddish brown precipitate, respectively, prove presence of Cu.
Precipitate Rh and Ir Dissolve in 20 ml. HC1 and 2 or 3 drops of 6 N HNOI. Divide solution into two equal parts. Make one part strongly ammaniacal. Evaporate to dryness. Take up with 10 ml. hot 6 N HCI. Yellow residue is Rh. Evaporate remaining part of solution with 5 ml. HhO.. When fumes of H2S0d are evolved add several drops of HNOI. A blue color confirms Ir
.
DISCUSSION OF THE PROCEDURE
Separation and Idenhjfcalion of Osmium.-The retort used to carry out the distillations by which osmium and ruthenium are separated from the other members of this group offers a very effective substitute for the expensive all-glass still and absorption train used for a quantitative determination (28). The thiourea test for osmium is very satisfactory. A definite pink color is produced with 0.01 mg. of osmium per milliliter of solution. None of the other platinum metals give the color (29). Separation and Identification of Ruthenium.-The bromic acid oxidation of ruthenium salts to the tetroxide permits the quantitative removal of ruthenium from a solution in a single distillation. After the destruction of nitric acid used in the oxidation of osmium, sulfuric acid is added to convert the chlororuthenate to ruthenium sulfate because volatilization of ruthenium tetroxide can be accomolished more raoidlv * , from a solution of this salt (30). In the c o n h a t o r y test for ruthenium it should be noted that enough of the ammoniacal solution of sodium thiosulfate must be added to render the solution tested distinctly alkaline. The violet color appears when most of the excess of ammonia has been boiled out.
Separation and Identification of Bismuth.-Experiments have shown that when solutions of bismuth chloride are treated with sodium bicarbonate until the pH of the solution reaches a value of 3, the filtrate from the precipitated bismuth salt does not yield bismuth sulfide on saturation with hydrogen sulfide. This precipitation of bismuth offers a very good qualitative method for the separation of bismuth from gold, palladium, copper, cadmium, platinum, iridium, and rhodium. Great care must he taken not to allow the neutralization of the solution to proceed to pH 4 since a t this point the precipitation of iridium begins (31). Cresol red is used to fix the proper hydrogen ion concentration. When the pH of the solution is not allowed to exceed 3 the precipitated bismuth salt will be pure white, whereas the presence of a small amount of iridium imparts a distinct brownish color. The c o n h a t o r y test used for bismuth is of the spotreaction type and is very easily carried out. When care is taken to avoid the presence of an excess of acid the cinchonine test for bismuth is sensitive to 1 part of the metal in 350,000 parts of water (32). The Separation and Identification of Gold.-The use of sulfur dioxide for the reduction of gold to the metallic
Filtrate Te, Au, Mo, As, Sb, Sn, Hg Dilute with an equal volume of water. Pass in SQ for fifteen minutes at 90'. Filter. Fillrate Sb, Sn. Hg, As, Mo Evaporate nearly to dryness. Dissolve residue in 15 ml. N HCI. Filter. Boil filtrate to remove SO3. Make nearly neutral with solid NaHCO, and saturate with H a s to precipitate last traces of Mo. Filter. Combine the precipitates and digest with 10 ml. 12 N HCI for several minutes a t 70'. Saturate with H d and then filter.
Filtmtc Sb, Sn Boil to remove H d . Reduce with Al. Filter. Filtrate Sn The filtrate is allowed to run into 0.1 N HgCIz. White or gray precipitate confirms Sn.
Precipitate Sb Dissolve in tartaric acid and H N G . Dilute, then pass HIS. Orange precipitate shows Sb.
Filtrate Mo Acidify with HCI. Add Zn metal and then 5 ml. of N KCNS. Red color is Mo.
Precipddc Te, Au Treat with 15 ml. 1-1 HNOa Filter Solution Te Evaporate to dryness. Dissolve residue in 3 or 4 ml. of N Pass NaOH. Heat to 90'. in SO2,then add HC1 drop by drop. Black precipitate is Te.
Residue Au Dissolve in dilute aqua re&. De~troyHNOs by evaporation t o dryness with HCI. Dissolve residue in 10 ml. H20. To a drop of the solution on filter paper add 1 dropof a 0.05 per cent. tetramethyldiaminodiphenylmethane solution in ten per cent. HOAc. Bright blue color confirm3 Au.
Precipitate Hg, As, Mo Add 25 ml. three per cent. H901. Heat to boiling and add N&OH drop by drop until alkaline to litmus. Filter. Filtrate As, M o Evaporate to volume of 10 ml. Add an equal volume of magnesia mixture. Allow to stand for 0.5 hour and then filter.
Residue Hg Dissolve in HCI and few drops of HNOJ. Destroy HNO.. Add SnCl?. White precipitate becoming gray or black is Hg.
Prccipilofe As Add solution of AgN08. Chocolate color proves presence of As.
state is a satisfactory analytical procedure as is shown by its use in the quantitative determination of gold in dental gold alloys (33). Attention must be directed to the fact that when the total amount of palladium in the original solution is as low as 1 milligram, nearly all of the metal will be precipitated with gold and must be tested for a t this point. Gold is quantitatively separated from palladium by reduction to the metal through the use of hydroquinone (34). Palladium is identified in the filtrate in the usual way by precipitation with dimethylglyoxime. Removal of any excess of hydroquinone is unnecessary. The Separation of Cadmium.-In the early stages of the development of this procedure cadmium persistently escaped detection. At several points in the procedure relatively large amounts of sodium chloride were filtered off and discarded. By a process of elimination it was concluded that any cadmium compound present must have been precipitated with sodium chloride. This was found to be the case, for, when the precipitated sodium chloride was converted to sulfate, cadmium was found to be present. Conversion to the sulfate was resorted to in order to insure the destruction of any complex anion containing cadmium. Only relatively high concentrations of cadmium give a precipitate with hydrogen sulfide in concentrated solutions of sodium chloride. The SeHration of Copper.-Precipitation of copper as cuprous thiocyanate as a means of separating this element from the platinum metals is used in a precise quantitative scheme developed for the analysis of dental gold alloys (35). It will be noted that a 10 molar solution of sodium hydroxide is used to neutralize the solution in which copper is to be precipitated by ammonium thiocyanate. Use of this extremely concentrated solution of sodium hydroxide serves to keep down the final volume of the solution from which copper is to be precipitated. Separation of Platinum from Rhodium and Iridium.The present procedure follows very closely the method devised by Gilchrist and Wichers (36). Practice will be needed by the student in fixing pH values with bromcresol purple and cresol red, but the accuracy required here is not as important as in the precipitation of bismuth. The Detection of Rhodium.-In the procedure used by A. A. Noyes (37), ammonium chlororhodite is converted into chloro-pentammino-rhodium chloride. The latter is insoluble in 6 normal hydrochloric acid. Iridium in quantities up to 2.5 mg. per milliliter remains in solution. SPECIAL REAGENTS
Cinchonine-Potassium Iodide.Stir 1g. of cinchonine with the least amount of nitric acid necessary to form a viscous mass. Dissolve the latter in 100 ml. of water and then add 2 g. of potassium iodide. Allow the solution to stand for forty-eight hours and then filter off any precipitate that may have formed. The reagent keeps indefinitely.
Dimethyl~henylbenzylammoniumChloride (38).-Mix equimolecular amounts of benzyl chloride and dimethylaniline and allow the mixture to stand at ordinary temperatures until a crystalline mass is formed. Wash the solid with ether to remove unchanged benzyl chloride and dimethylaniline and recrystallize the residue from ninety-five per cent. ethanol to obtain colorless crystals melting a t 110'. The insoluble compound formed with tetravalent platinum is presumably [(CHs)a(GHs)(CsHsCH2)IzPtCls. Sodium Hydrogen SulMe Reagent.--Saturate a 3 N solution of sodium hydroxide with hydrogen sulfide. In a liter of this solution dissolve 4 g. of sulfur and 3.5 g. of sodium hydroxide. Let stand for twenty-four hours and then filter. PART I11 THE ANALYSIS OF DIVISION
B*
Directions were given in Part I for the separation of the sulfides into Divisions A and B by the use of a special sodium hydrogen sulfide reagent. The latter dissolves the sulfides of selenium, tellurium, gold, antimony, tin, arsenic, mercury,. and molybdenum. OUTLINE OX' A PROCEDURE FOR THE ANALYSIS OF DIVISION B O F GROUP n
Solution.-Thio salts of Se, Te, Au, Mo, As, Sb, Sn, Hg. Acidify with 6 N HCI. Saturate with H a . Filter. Boil precipitate with dilute aqua regia. Dilute with equal volume of water, then filter from S and paper pulp. Evaporate filtrate to dryness with HCl. Pass SOe for five minutes. Filter. DISCUSSION OF THE PROCEDURE
The Isolation of Selenium.-In 12 N hydrochloric acid a t ordinary temperatures selenium is precipitated by sulfur dioxide with no contamination by tellurium (39) or gold. Separation and Identification of Gold and Tellurium.Both of these elements are completely precipitated by sulfur dioxide from 6 N hydrochloric acid a t a temperature of 90'". ~ e l l u r h mis readily soluble in 1-1 nitric acid while gold remains undissolved. The latter is readily identified by the oxidizing action of auric ion on tetramethyldiaminodiphenylmethane. This test is specific for gold, since a t this point in the procedure none of the ions of the other elements in the sub-group give a color reaction with the reagent. Separation of Antimony and Tin from Arsenic, Mercury, and Molybdenum.-The solubility of the sulfides of antimony and tin in 12 N hydrochloric acid has long been used to separate these elements from arsenic and mercury. It was found that molybdic acid was also insoluble in the acid, and could thus be separated from antimony and tin.
-
*Abstracted from theses presented to the University of Minnesota by H. H. Barber and J. L. Maynard.
SUMMARY
A procedure has been prepared for the qualitative separation and identification of the metals found in Group 11. Germanium alone has been omitted because of its extreme rareness. The metals included
in the scheme are selenium, tellurium, gold, antimony, tin, arsenic, mercury, molybdenum, osmium, rutbenium, rhodium, iridium, platinum, palladium, copper, bismuth, and lead. The procedure has been designed to handle not less than one or more than fifty milligrams of each element.
LITERATURE CITED
(1 SNEED,J. A m . Chcm. Soc.. 40, 188 (1918). (21 NOYES,A. A., "Qualitative chemical analysis," 9th Ed., The Macmillan Co., New York City, 1926, p. 71. (3) SNEED,LOG. tit., p. 187. (4) KNOX,J. Chem. Soc., 95, 1763 (1909). (5) BARBER,H. H., "Separation of the copper arsenic group." Them submitted t o the Graduate Faculty of the University of Minnesota, 1926, p. 32. ( 6 ) SNEED,M: C., AND G. B. HEISIG,"Revised procedures for qualitatwe analysis," Burgess Publishing Co., Mimeapolis, Minnesota. 1937, 74 pp. (7) HILGER, SISTER MARIE. "The detection of pallasium, tellurium, and selenium." Thesis submitted t o the Graduate Faculty of the University of Minnesota, 1923, 16 PP. (8) WEBER,L. J., "The detection of osmium, ruthenium, rhodium, and iridium." Thesis submitted t o the Graduate Faculty of the University of Minnesota, 1924, p. 11. (9) BARBER, op. cit., p. 35. (10) KNOX,lot. cit. (11) HILLEBRAND. W. F., AND G. E. F. LWDELL, "Applied inorganic analysis," John Wiley and Sons, New York City, 1929, p. 276. JR., m OGBURN, J. A m . Chem. Soc., 46, (12) HOWE,HOWE, 335 (1924). (13) DEVILLEAND DEBRAY.C h m . N m , 1, 85 (1860). (14) CLAUS,Chem. News, 7, 115 (1863). (15) GIBES,ibid., 3, 130, 148 (1861); ibid., 9, 121 (1864). (16) BUNSEN,Ann., 146, 18 (1868). (17) MYLIUSAND DIETZ,Ber., 31, 3187 (1898). 3. SOC.Chem. Ind.,31, 1036 (1912). 18) KOUKLINE, 2. anal. Chem., 52, 740 (1913). 19) WUNDERAND THORINGER,
s MAZZAUCCHELLI, Qid., 89, 1 (1914). (20) M n ~ u AND (21) FRIEND, J. N., "Textbook of inorganic chemistry," Charles Griffin & Co., Ltd., London, 1922, Voli IX, Part I, p. 342. (22) WEBER,op. cit. (23) NOYES,A. A., AND W. C. BRAY,"Qualitative analysis for the rare elements," The Macmillan Co., New York City. 1927, 536 pp. (24) GILCBIST AND WICHERS,J. A m . Chem. Soc., 57, 256&73 (1935). (25) Ref. 24. 2566. (26) K o ~ ~ ~ oI.a M., a , AND N. H. FURBUN, "Volumetric analyse, John Wi!ey and Sons, New York City, 1929, Vol. 11. "Practical pnnciples," p. 502. (27) Ref. 11, p. 143. (28) GILCHEISTAND WICHERS, loc. cit., p. 2566. (29) SINGLETON, Ind. Chemist, 3, 121 (1927). (30) G ~ ~ c a n rAND s r WICHERS,loc. cit., p. 2568. (31) GILCHRIST AND WICHERS,Paper No. 178 of the Scientific Program of the Ninth International Congress of Pure and Applied Chemistry, Madrid, 1934. Tomo VI, "Quim~ca Analitica," p. 37. (32) FEIGL AND NEUBER,2. am1. Chem., 62, 372 (1923; cf. LEGER,ibid., 28, 347 (1889). (33) SWANGER, W. H., "Analysis of dental gold alloys," Scientific Papers of the Bur. of Standards, No. 532, 1926. (34) BEAMISR, RUSSELL AND SEATH, Ind. Eng. Chcm., Anal. Ed., 9, 174 (1937). (35) SWANGER, loc. cit. (36) CJ. Ref. 24. (37) CJ. Ref. 23, p. 143. (38) M I C ~ EAND R GRADMANN, Ber., 10, 2078 (1877). (39) CJ. Ref. 11, p. 261.
