MICROCHEMICAL QUALITATIVE ANALYSIS without SULFIDES E. M. GERSTENZANG 1560 East 32nd Street, Brooklyn, New York
Microchemistry has in the last feu, years become of tremendous scientific and industrial importance. Aside from vastly improwing the technic of the experimenter. it has rendered possible, using only a few milligrams of substance, the complete anelysis and identification of such materials as hormones and actinre principles of drugs, obtainable in minute quantities at tremendous expense.
As for an alternative suIf;de-less method of qualitative analysis, the mere idea speaks for itself. Although the use of the microscope is unnecessary with this method the beginner in qualitative analysis should become accustomed to handling minute quantities of substance with facility and ease.
mediately available in the home laboratories of countless numbers of students and amateurs, which was N 1930 BROCKMAN of the University of Georgia virtually impossible heretofore, because of the hydropublished a system of qualitative analysis (1) gen-sulfide nuisance. wherein the use of the sulfides as group reagents For a brief resume of the history and practice of was eliminated. This radical departure from the classical method is of great interest and should prove a microchemistry and microchemical analysis, as well as stimulus to research in analytical chemistry. For a a list of references to the subject, the article of Engelder concise discussion of Brockman's method, the reader is and Schiller should be consulted (5). referred to a review (2) of the system by Browning of THE METHOD Yale. As to the "why and wherefore" of such a system, the preface to Brockman's book is very enlightenThe method to be described might appropriately be ing. In reviewing the book, Browning says, "so far as called "centrifuge analysis" because of the constant the reviewer knows this is the first textbook which has use and importance of the hand centrifuge. When the seriously placed it" (a sulfide-less method) "before the extreme rapidity of centrifuge methods, especially on a hydrogen-sulfide-gassed worker in qualitative analysis." microchemical scale, is compared with the convenHowever, it may be of interest that some years ago tional, nenre-straining filtration methods, the value of I ran across a scheme entitled "Zettnew's Scheme for the centrifuge becomes highly apparent. Qualitative Analysis without the Use of Hydrogen Sulfide or Ammonium Hydrosulfide, Arranged by H. C. APPARATUS Bolton, Ph.D.; for the Students of the School of Mines, Columbia College" (3). The reason that this system (1) Two-tube hand centrifuge.-The most important bas been forgotten is probably to be found in the piece of apparatus. By means of the centrifuge all lengthy, cumbersome operations and imperfect separa- separations of precipitates from mother liquids are tions that it involved. conducted, as well as the washing of precipitates. The Although, as Browning points out in his review, centrifuge virtually eliminates the use of filter paper Brockman's method suffers from the defect that it and funnels. does not include a t least some of the so-called "rarer" ( 2 ) Test-tubes.--Of approximately the following metals, the method herein presented likewise includes dimensions: 1 cc., 5 cm. X 0.6 cm. ; 4 cc., 7.5 cm. X only the "common" metals. The "rarer" elements, 0.9 cm.; 10 cc., 10 cm. X 1.2 cm. These can be bought particularly those that are now of commercial impor- ready-made or in the case of the one and four cubic tance, such as beryllium, titanium, vanadium, and centimeter tubes can be blown from glass tubing. molybdenum, will be included in a paper upon which (3) Test-tube racks.-These can be constructed by work is now being done. Apropos of the so-called drilling holes in solid blocks of wood, or makeshifts "rare" elements and their relationship to qualitative may be made by puncturing- holes in shallow paste~. analysis, mention should be made of the discussion board boxes. (4) by Spoerri of the Polytechnic Institute of Brooklyn. (4) Microbeake7s.-These beakers can be made by sized A factor of no little importance is that the use of a cuttine off the lower oortions of aonronriatelv =. sulfide-less method renders analytical chemistm im- test-tubes and then flattenina the convex surfaces in a HISTORICAL CONSIDERATIONS
I
-
.
hot flame. They should be of five and ten cubic centimeters capacity. are constructed by (5) Capillary pipets.-These drawing out the ends of sections of glass tubing and fitting them with rubber bulbs. (6) Reagents and reagent bottles.-The reagents are kept in dropper bottles of one fluidounce capacity. Those in use in the author's laboratory, manufactured by the Owens-Illinois Glass Company, andvery cheaply procurable through any wholesale druggist, are made of green glass and are equipped with droppers passing through Bakelite screw-caps, by means of which the bottles are kept hermetically sealed. The volume of a drop delivered by the dropper of these bottles is approximately 0.06 cc. Bottles stoppered by the rubber bulbs of the dmppers are unsatisfactory, for the droppers "jump" out of the bottles when the lower surfaces of the bulbs become moist. Of course, reagents, like concentrated acetic acid, the fumes of which attack rubher, should be preserved in 30-cc. glass-stoppered bottles, from which the necessary reagents are removable by medicine pipets which are kept, when not in use, in appropriately labeled 4-cc. test-tubes which stand in the rack. (7) Absorbent cotton.-In the unusual case wherein a precipitate is removable from the mother liquor, with is of aid' centrifuging, a suCfion A tiny tuft of cotton is tightly twisted about the mouth of the capillary pipet, after which i t is used to draw up the liquid in the normal fashion, Cotton is also used in stoppering the tubes in which group centrifugates are presenred for subsequent examination. (8) Copper lift-wires.-These are thin copper wires about fifteen centimeters long which have been twisted is just large enough into a noose at One end. The to permit a 4-cc. tube to Pass through and to rest upon it hv means of These are used to raise or -. ~, - - the - flanee. to lower the tubes out of or into the metal tubes of the centrifuge. (9) Thin Pyrex rod-for stirring purposes. (10) Platinum w i r e f o r flame tests. (11) White glazed porcelain spot-phte--used in flame tests and for occasional ion tests. ~
0
~
OPERATIONS
removed. The residue is washed by filling the tube half full of hot water (unless otherwise indicated), thoroughly shaking, or stirring with the Pyrex rod, and centrifuging. The centrifugate here obtained is usually rejected. Washing, as customary, should be repeated as often as necessary. (3) Evaporations.-Evaporations are carried out in microbeakers by very carefully heating with the Bunsen burner upon the wire gauze. Great care should he taken to prevent spattering. (4) Alkalinity or acidity test.-The reaction to litmus is determined by dipping the Pyrex rod into the solution and drawing it across the test paper. ( 5 ) Cleaning capillary pipets.-Three beakers, one of which is filled with water, are provided. After a pipet has been used it is cleaned by pouring some water into the second beaker, drawing up some of it into the capillary pipet, and then ejecting the contents into the third or waste beaker; the process is repeated several times. REAGENTS
Unless definitely specified otherwise, all reagents are of the concentrations stated in Treadwell-Hall (6). PROCEDURE
The ,,unknown,, solution consists of the chlorides and nitrates of the common cations. The volume of solution taken for ex. amination should not exceed one cubic centimeter. Place the solution in a 4-cc. tube. add ten drops of dilute HCI (test with litmus), stir with the Pyrex rod, add ten drops of water, stir again, and centrifuge. Remove the centrifugate andpreserveit in a 4-cc. test-tube labeled "A." The residue comprises, after washine with a few droos of cold water: Grouo I-AaCl. . PbC1,. ~ ~ ~ ~ l ~ y
Analysis of Group I T o the residue in t h e 4-cc. tube add 2 cc. cold water, cautiously heat almost t o boiling, and centrifuge. T o the centrifugate add three drous of KCrO, solution. A vellow orecioitate indicates . . the presence of 1 2 . The residue washed free from lead with hot water is treated with eight drops of concentrated aqua ammonk, stirred well, and centrifuged. A blackened residue indicates the presence of mercurous mercury. Place two drops of the centrifugate in a k c . test-tube, acidify with one or two drops of concentrated HNOa. A white precipitate of AaCl indicates the oresence of silver. The c o k t of test-tub; "A" is transferred to a 10-cr. beaker, treated with five drops of 3% HH~OB, and boiled (a). It is now made strongly alkaline with a concentrated solution of K&OI (b). A volume of solution of KOH equal t o that of the solution in the beaker is now added, together with ten drops of saturated Br2 solution (6). The mixture is boiled and stirred very cautiously for one or two minutes, after which i t is centrifuged. The centrifugate is preserved in test-tube "B." The residue is thoroughly washed, and it then comprises: Groups I1 and III-HgO. HBiOa, CuO, Cd(OH)%.PbO,, Ni(0Hh. HsMnOl. CO(OH)~. Fe(OH)r, CaCOs, BaCOa. SrCOa, M~COI.
(1) Centrifugation.-Precipitates are separated from their mother liquors by centrifugation in place of the classical operation of filtration. Needless to say, single samples should always be counterbalanced by water tubes. Hereafter the clear liquid obtained by centrifuging and corresponding to the filtrate in filtration will he called the centr$ugate. (2) Washing of preci~tates and residues.-InasNotes on the Preci@'talion of Groups II and III much as precipitates usually coalesce into a very compact mass upon centrifugation, the supernatant liquid (a) To reduce MnOl- to Mn*. can be easily removed by means of simple decanta(b) Potassium carbonate is used t o precipitate completely the tion or by means of a capillary pipet, the tip of which alkaline earths, which would be only partly precipitated if potassium hydroxide alone were used. is slightly curved. By tilting the tube and placing the ( c ) Bromine solution is used t o precipitate lead, speed u p curved tip of the pipet against the lower edge of the the conversion of cations to anions, precipitate manganese comcompact precipitate, all the supernatant liquid can be pletely, etc.
+ + + + +
+ +
P h + + 20Br-.--t Ph02 4 2BrCrf++ 40H- +Cr022H20 2Cr0,30Br20H-+2Cr04-MnC' 2 0 H - -+Mn(OH)r ( Mn(OH), OBr- --+ HzMn01+ Br-
+
+ 3Br- + HnO
1 1 Separation of Groups II and 1 The residue is treated with six drops of concentrated hydrochloric acid and four drops of 3% hydrogen peroxide (a), stirred and warmed if necessary. The resulting solution is treated with about 15 mg. of ammonium chloride (b) and then with a sufficient number of drops of concentrated aqua ammonie and four drops of hydrogen peroxide (constantly stirring) t o render the solution distinctly alkaline. Centrifuge and preserve the centrifugate in test-tube "C." The residue is washed thoroughly with cold, very dilute aqua ammonie. (1,p. 20). The residue now constitutes: Group 11-HgNHzCI. Bi(0H). H2MnOs. Fe(0H)r. Ph(OH)*. Nola on the Separation of Group II from Group III (a) I n the presence of H.02 many oxides and hydroxides which are insoluble in certain acids or dissolve with great difficulty, dissolve in these acids readily. Thus, manganese dioxide which is insoluble in acetic acid, readily dissolves if HSO2is added and liberates oxygen, half of which apparently comes from the manganese dioxide and half from the hydrogen peroxide. (b) To keep magnesium in solution.
'
Centrifuge the mixture, discard the centrifugate, and wash the residue. Dissolve the residue in eight drops of dilute HCI and five drops of H%O1and heat t o hoiling. To three drops of the resulting solution add five drops of concentrated HNOr and hoil (a) down t o about one-fourth of a cubic centimeter or almost t o dryness. Add three more drops of concentrated HNOI and about 15 mg. of PhO, and heat t o boiling. Dilute with 1 cc. of water and centrifuge. A pink supematant liquid indicates the presence of manganese. Evaporate the remainder of the solution almost to dryness. t o decompose excess HBO,(b). Dilute with five drops of water and add three droos of SnCI. solution: allow t o stand for five minutes. A white to gray or black precipitate indicates the presence of mercuric mercury. Notes on the Analysis of Group I I B (a)
+ 5Ph02 + 4H+--f
2Mnt+ 2HMnO.
+ 14HCl-
8HaO
5Ph++
+ 2H.O + 2Mn0,-
+ 2MnCln + 5C12t
Therefore hydrochloric acid must be eliminated t o prevent it from interfering with the test for manganese. ( b ) Excess Ha02 must he decomposed a s otherwise Sn++ would he oxidized t o SnC+++,thereby preventing it from reducing Hg++ to Hg*++. Analysis of Group III
The contents of test-tube "C" are diluted with ten drops of water, and then treated with eight drops of solution of NeHPO, and five drops of concentrated aqua ammonie, which causes the Separation of Lioup IIA from Group I I B Dissolve the residue in ten drops of concentrated CIgCOOH precipitation of: Group III-Ca8(P04)p, Sra(P0,)~. B~~(POA)I. MgNH,P04. and ten drops of 3% H20z; then add ten drops of solution of The mixture is centrifuged; the centrifugate heing preserved NasHP04 (even if the residue d w s not completely dissolve). in test-tube "E" while the residue is thoroughly washed with Bring the mixture t o a hoil and centrifuge. Preserve the centrifugate in test-tube "D." Wash the residue thoroughly. I t now very dilute aqua ammonie. The residue is now dissolved in fifteen drops of dilute acetic arid and the resulting solution is constitutes: Group 11-FePO., BiP04, PbJ(POJc treated with five drops of solution of potassium chromate. A Analysi~of Group IIA yellow crystalline precipitate of barium chromate indicates the presence of barium. Centrifuge off the precipitate, preserve The well-washed residue is treated with 1 cc. of solution of KOH and heated t o hoiling. Centrifuge the mixture, dilute t o the centrifugate for further tests, and wash the residue. Mix the 3 cc. (a), and t o the clear centrifugate add an excess of 3% residue with three or four drops of water, and transfer to the HrOs. The formation of a yellow precipitate indicates the pres- cavity of a spot-plate. To the mixture on the spot-plate add two drops of concentrated hydrochloric acid. With a platinum ence of lead (b). The residue from the lead separation is thoroughly washed and wire, which has alternately been dipped into concentrated hydrodissolved in ten drops of hot, dilute HCI. To four drops of the chloric acid and then held in a colorless Bunsen flame until it no cold solution add ten drops of freshly prepared potassium stannite longer colors the flame, a "flame test" is run upon the mixture. solution and stir with the Pyrex rod. A jet-black precipitate An apple-green flame coloration indicates the presence of barium. The centrifugate from the barium chromate separation is should he identified as metallic bismuth ( c ) . To the remainder of the solution, diluted with 1 cc. of water, treated with ten drops of dilute sulfuric acid and heated t o add two or three drops of &Fe(CN)a solution. A deep blue hoiling (a). A white crystalline precipitate of strontium sulfate indicates the presence of strontium. Centrifuge, and treat the precipitate indicates the presence of iron. residue with five drops of solution of ammonium sulfate. CentriNotes on the Analysis of Group IIA fuge again and combine the ammonium sulfate centrifugate with (a) The solution must he diluted, as Bi(OH)8 is somewhat .the acid centrifugate obtained in the immediately preceding soluble in concentrated KOH. operation (b). Wash the residue and proceed with a flame test as f o barium. ~ A beautiful crimson flame coloration confirms the presence of strontium. To the solution from the strontium sulfate separation add potassium carbonate solution to alkalinity. Boil the mixture and centrifuge. Discard the centrifugate. Dissolve the residue (c) Upon warming a solution of potassium stannite or upon allowing it t o stand for a long time, the following changes take in five drops of dilute acetic acid. Add five drops of solution of place: ammonium oxalate. A white, crystalline precipitate of calcium oxalate indicates the presence of calcium. This precipitate may in dilute solution, HSnOl- +OHSnO 4 (black); form immediately or after several minutes. Centrifuge the mixin concentrated solution, 2HSn02- -+Sn0,--+ H*O+Sno 4 ture, wash the residue, and apply the flame test. A yellowish red ' (black) flame coloration indicates the presence of calcium. Therefore in testing for bismuth the solution of potassium stanTo the centrifugate from the calcium axalate separation add nite must he made immediately before use by adding an excess of fifteen drops of concentrated aqua ammonie, five drops of amKOH t o a few drops of stannous chloride solution. monium chloride solution, and ten drops of disodium phosphate solution. Rub the sides of the test-tube with the Pyrex rod. Analysis o j Group I I B A white, crystalline precipitate (MgNH4P04) indicates the Make the contents of test-tube "D" alkaline with solution of presence of magnesium. KOH and then add an excess of eight drops. Add five drops of A test for magnesium, even in the presence of Caf+, BaC+, H90z and heat t o hoiling. This causes the precipitation of: Srf+, is ohtained by adding t o the ammoniacal solution of these HgO. Group IIB-H.MnO8. cations, one or two drops of 8-hydroxyqninoline, which causes a
+
yellowish green precipitate of (C9HsNO)&fg t o form even in the presence of very minute quantities of magnesium.
Separation and Analysis o j Group V The contents of test-tube "B" are evaporated to about 2 cc. and acidified with dilute hydrochloric acid. Heat but do not Notes on the Analysis of Group III boil (to expel any bromine remaining from Group I1 treatment). (a) In the presence of comparatively large quantities of Add about 10 mg. of sodium chloride (to keep aluminum hyC a t + , some calcium sulfate may be precipitated. Although droxide out of colloidal solution), and then to the warm solution calcium sulfate is less soluble in hot water than in cold water. in add a slight excess of dilute aqua ammoniae which precipitates: the prerr.nce of excess acid, it lurrns the rohthle Ca(llSO,),. Group V-HSbOa, Sn(OH)., AI(OI&. ( 6 ) This is done to renmrc all traces of calcium due t o thc Centrifuge off the precipitate, preserve the centrifugate in test fact that a soluble complex salt, (SII.)?Cn(SO,),, is f.>rrr.cd tube "G." and wash the residue with a mixture of five drops of dilute aqua ammo~s?,fifteen drops of dilute sodiumchloride Analysis of Group I V solution, and five drops of 3% hydrogen peroxide (a). Finally, The contents of test-tube "E" after evaporation t o about 1cc. wash the residue with several cubic centimeters of boiling water is treated with 1cc. of potassium hydroxide solution and 2 cc. of containing a little sodium chloride. Dissolve the residue in water. The mixture is again evaporated t o 2 cc. and is treated several drops of hot dilute hydrochloric acid. To one or two once mare with 1 cc. of potassium hydroxide solution and with drops of solution add three drops of ammonium carbonate soluten drops of saturated bromine solution (a). This will cause the tion, three drops of concentrated aqua ammoniae, ten drops of precipitation of: Group IV-CuO, Ni(OH)a, CO(OH)~, Cd(OH)%. water, and, finally, two drops of 0.10% aluminon solution. A Centrifuge off the precipitate, discard the centrifugate, wash bright red precipitate indicates the presence of alumimm. the residue, and dissolve i t in ten drops of hot, dilute hydrochloric To one-half of the remaining solution add a fragment of bright acid. Dilute the resulting solution t o about 1.5 cc. and add in lead foil and five drops of concentrated hydrochloric acid. the order named about 1cc. of freshly prepared solution of sodium Warm slightly and set aside for a few minutes. A jet-black coatsulfite and 1cc. of solution of potassium thiocyanate (b). Heat ing of metallic antimony, upon the surface of the foil, which disthe mixture almost t o boiling. A white precipitate of cupraus solves upon the addition of a few drops of bromine water t o the thiocyanate indicates the presence of copper. Centrifuge the acid solution, proves the presence of antimony. mixture and wash the residue thoroughly. Treat the residue The remainder of the solution is evaporated to ahaut one-third with three drops each of 3% hydrogen peroxide and concen- its volume, treated with five drops of concentrated hydrochloric trated aqua ammonie (c). A deep blue color confirms the pres- acid and a few milligrams of reduced iron and warmed. When ence of copper. reaction subsides the mixture is centrifuged and to the clear This may be further confirmed by acidifying the blue solution centrifugate, three or four drops of mercuric chloride solution with dilute hvdrochloric acid, diluting to about 3 cc. with water. are added. A white t o gray precipitate of mercurous chloride or and adding a few drops of potassium ferrocyanide solution, mercury proves the presence of tin. whereupon a reddish brown precipitate of cupric ferrocyanide will be formed. Notes on the Anelyris of Group V The centrifugate from the cnprous thiocyanate separation is (a) This mixture is used t o oxidize any traces of Cr(OH)a, made ammaniacal with a few drops of concentrated aqua amwhich might be present and which would impart a green tint t o monk. To five drops of the resulting solution diluted with the group, to Cr04--. water t o about 1 cc. add three drops of solution of dimethylglyoxime. A ruby-red precipitate of nickel-dimethylglyoxime Analysis o j Group VI reveals the presence of nickel. T o a fresh portion of five drops of the solution add five drops To a small portion of the contents of test-tube "G" add two of concentrated acetic acid and two dropsof a-nitroso-@-naphthol. drops of solution of potassium ferrocyanide. A white precipiA purple-red precipitate indicates the presence of cobalt. tate of zinc ferrocyanide indicates the presence of zinc. To the remaindei of the solution add 1 cc. concentrated acetic A second small portion is acidified with dilute sulfuric acid, acid and ten drops of sodium pyrophosphate solution (10 g./cooled, and t o it two or three drops of 3% hydrogen peroxide are 100 cc.). Boil (d). A white precipitate of cadmium pyrophos- added. A violet coloration which becomes much lighter a t the phate indicates the presence of cadmium. Centrifuge the mix- end of about one minute or very rapidly upon warming indicates ture, discard the cenhifugate, wash the residue, and dissolve it in the presence of chromium (a). several drops of dilute nitric acid. Dilute the resulting solution The balance of the solution is made strongly acid with concent o about 2 cc. and add several drops of potassium fenicyanide trated hydrochloric acid and a fragment of bright copper foil is solution. A yellowish precipitate of cadmium fedcyanide con- added. The mixture is warmed (not boiled) and set aside for fifteen minutes. A steel-gray coating of metallic arsenic upon 6rms the presence of cadmium. the surface of the foil, soluble in solution of potassium hypoNotes on the Amlysis of Group I V bromite, proves the presence of arsenic. Of course, if preferred, (a) The evaporations with potassium hydroxide are carried the very sensitive Marsh or Gntzeit tests may be used. out t o decompose and volatilize ammonium compounds which would interfere with precipitation of the group. The bromine Notes on the AnaZysis of Group VI solution destroys all remaining ammonium compounds in addi(a) The reactions involved are: tion t o preventing some copper from remaining in solution. [Cn(OH)* is slightly amphoteric and dissolves in hot concenHnCrrOi 7Hs02 +2HaCrOa f 5H20 trated potassium hydroxide.] 2HCrOs 3HL3O,+ Cr2(SO4)~ f 6Hx0 -k 502 t ( b ) Upon long standing in solution sodium sulfite is oxidized The sensitivity of the test is considerably increased if the acidified t o sodium sulfate. chromate solution is shaken with a little ether before and after The reactions involved are: the introduction of the hydrogen peroxide. The ether layer Cu++ SO, 2Hn0 +Cu+ SO4-4HC assumes an intense blue color. Cu+ CNS- -+CuCNS 1 (white) ~
~~~
+
+
+ +
+
+
+
(c) Hydrogen peroxide reacts with the precipitate, converting copper t o the cupric condition which then reacts with the aqua ammanie comer-ammonia com~lex. ~ ~ - t o~form ~ the ~ characteristic ( d ) Sodium pyrophosphate is made by heating disodium phosphate in a crucible t o dull redness. ~
~
~~
..
2NadiPO1 -+ Na4Pn0,
+ HsO t
Analysis of Group VII-The
Alkdies
Tests fdr the alkalies arc made upon portions of the original sample. Abuut 0.5 cc. of the original solution is placed in a 4-cc. test-tube and treated with an excess of solution of potassium hydroxide. The solution is carefully heated t o about 90' while a strip of moist red litmus paper is held about a centimeter over
.
the mouth of the tuhe. A change of color in the litmus from red to blue indicates the presence of ammonium ion. The presence of ammonium ion is con6med by holding the end of a glass rod which has been dipped into concentrated hydrochloric acid over the mouth of the tuhe. Dense white fumes of ammonium chloride are formed if ammonium compounds are present. Centrifuge the mixture used in the ammonium test, and discard the residue. Acidify the centrifugate with dilute hydrochloric acid and run a "flame test" upon the resulting solution. A yellow flame coloration lasting a t least onequarter of a minute proves the presence of sodium. To a new 0.5-cc. portion of the original solution add an excess of sodium hydroxide. After centrifuging, test the centrifugate by the flame test. View the flame through a piece of cobalt glass. A violet-colored flame shows the presence of potassium. OUTLINE OF GROUP SEPARATION
Treatment with hydrochloric acid precipitates: Group I-AgCl, PhClp,Hg,Clz. The centrifugate is preserved in test-tube "A," The contents of test-tube "A" are treated with solutions of potassium carbonate, potassium hydroxide, and hromine, which precipitates: Groups 11 and i l l - - H g O , HHiO,. CuO, Cd(OIOr. PbO,, Fr(011)s. Ni(OH),, Co(OH),. HJln01, CaCO,. IiilC01, SrCO,, NECOX. The centrifueate is oreserved in test-tube "B." The Grouos I1 and 111 preci&atr i; dissolved in hydrochloric acid-hydrogen peroxide mixture and the resulting wlutton is treated with ammonium chloride, an.monium hydruaide, and hydrogen peroxide. which precipitates: Group IT-HgNI4CI. Bi(OHh, HzMnOJ, Fe(OHh, Ph(OH)n.
The centrifugate is preserved in M - t u b e '"2." The contents of test-tube "C" are treated with solutions of disodium phosphate and aqua ammonix, which precipitates: Groap ZII-CafiPO,)t. Sra(l'O&. Ilas(P04),. .\IgNH4P0,. Thc centrilusate is urcserved iu test-tube "E." The contents of test-tube "E" are treated with solutions of potassium hydroxide and bromine, which precipitates: Group IV-CuO, C ~ ( O H ) Z Ni(OH)r, , CO(OH)~. The centrifugate is discarded. The contents of test-tube "B" are treated with dilute hydrochloric acid, then with solution of sodium chloride and aqua ammonk, which precipitates: Group V-HSbO. Sn(OH),, AI(OH)S. The centrifugate is preserved in test-tube "G." Thecontents of test-tube " G are tested by individual tests for members of: Group VI-ZnOa--, CrO,--, As0,---. A fresh sample of the original solution is tested for the presence of: Group VII-NaC, K+, NH,+. LITERATURE CITED
BROCWMN,C. J., "Qualitative analysis," Ginn & Co., Boston and New York City, 1930. P. E.. review of C. J. B R O I X ~ N ' S"Qualitative BROWNING, analysis," J. CFIEM.Euuc., 7,1217-8 (1930). Mom, H. A.. JR., "The chemist's manual," D. Van Nostrand Co., NewYork City, 1877. SPOERRI, "R81e of microchemistry in chemical education," J. CFIEM.Enuc., 10,491-3 (1933). AND SC~ZLER, "A system of qualitative mi-+ ENGELDER analysis," ibid., 9, 1 6 3 6 4 (1932). TREADWELL-HALL, "Analytical chemistry." Vol. I, John Wiley &Sons. Inc., New York City, 1926.
