QUALITATIVE ANALYSIS w i h u t HYDROGEN SULFIDE* C. J. BROCKMAN University of Georgia, Athens, Georgia
I
T IS necessary in a business concern to pause a t least once a year to take an inventory of its present state of affairs. This is essential for the safety of the stockholders, as well as for the health of the organization. It is advisable--even highly advisable-for an individual to undergo an annual physical examination, not only to determine the present status of deterioration or disease, but also to be a forewarning to future difficulties.
Presented before the Division
of Chemical Education at the ninety-third meeting of the A. C. S., Chapel Hill, North Carolina, April 14, 1937.
Is it not, therefore, advisable, or a t least appropriate, to take stock, so to speak, of the present status of qualitative analysisnot to determine only the present disabilities, but to look into the future and prognosticate some possible difficulties which may arise? Qualitative analysis has been practiced for many years. The first efforts were necessarily hit-or-miss, and I am in no position to say whether the hit or the miss predominated. Then in the hands of the first Fresenius. there was develo~edthe scheme method. -, or -systematic analysis. This procedure called for a sort of scheduled addition of reagents in a prearranged order, with appropriate filtrations, resolutions, and the
like, in the process of which the formation of char- control of the experimental conditions, such as pH, acteristically colored precipitates indicated the pres- concentration, temperature, and so forth, which canence of certain elements or, as we now say, of ions. not be met for any one cation when a large number of The absence of these precipitates, of course, indicated other ions are present. On the other hand, this statethe absence of such substances. This eliminated the ment applies to any scheme of analysis and is not a diffihit-or-miss method, so that the analyst was certain that culty inherent in the hydrogen sulfide scheme only. The steady neglect of this viewpoint has led to the no element was overlooked. According to Fresenins, the basis of the more im- development of many books concerned with theoretical portant or group separations required the use of hydro- qualitative analysis. But more than this, i t has almost gen sulfide. To a chemist, hydrogen sulfide is not taken experimental chemistry out of qualitative analyunpleasant in odor; one becomes immune to it, but to sis, so that now our qualitative analysis has been conthe uninitiated, it is temble. verted into a study of the physical chemistry of soluAs chemists, we have probably developed such an tions of electrolytes. There was a time when the immunity to the odor of hydrogen snlfide that we do not visible characteristics of inorganic compounds were recognize it as a deadly poison. The literature of our studied systematically. It is too much to require that science is replete with studies of the poisonous nature all this information be obtained in an elementary of this foul-smelling gas. I only quote one value, course in chemistry. Most textbooks on inorganic namely, that in concentrations as low as 0.05 per cent., chemistry give just passing mention to many of the by volume in air, hydrogen sulfide may be fatal; when, compounds of the metals. Therefore, it is essential by virtue of an individually strong resistance, a victim that this information be garnered by a close study of escapes death, then he a t least suffers some major these compounds in the qualitative laboratory where physiologic dist~rbances.~Hydrogen sulfide is a very equations should be written and understood. The theory which has been developed around hydrodefinite industrial poison and is so considered, except by most teachers of qualitative analysis. This condi- gen sulfide precipitation has put the cart before the tion may be the result of the force of circumstances horse to the extent that a student can calculate the in that huildmgs and equipment are antiquated, or it number of milligrams of cadmium ions left in a solution containing 0.1 N hydrogen chloride a t 25OC. after may be that it is inertia on the part of the teachers. Please do not misunderstand my attitude in pre- saturation with hydrogen sulfide, but he does not know senting this discussion. I am condemning no one, nor that ammonium polysulfide [(NH4),S,] is a very poor am I casting aspersions on any of the accepted pro- reagent for qualitative separations. That the scheme of hydrogen sulfide separations is c e d u r e s I am taking an inventory of present practices in the art and science of teaching qualitative analysis. lacking in refinement is indicated by the enormous I have been interested in qualitative analysis without number of modifications of the separations within the hydrogen sulfide for about fifteen years, and there is major groups, which have appeared in the literature. nothing sacred, if I may use the expression, in a pro- Of course, some of these are improvements, and some cedure with or without hydrogen snlfide. As a peda- are makeshifts. On the other hand, I have records of a t least thirty gogue I am interested in the methods of teaching qualitative analysis. By "methods" I do not give to methods of schematic analysis for the usual metal ions this word the meanings which are usually assigned to in which hydrogen sulfide has. been eliminated. Some it by departments and professors of education. So of these make use of reagents, which evolve hydrogen aside from the physiological aspects of hydrogen sul- sulfide and so use the hydrogen sulfide groupings fide, let us inquire into the methodology of qualitative without the undesirable features of hydrogen sulfide. Then, there are methods in which the whole list of analysis. With the development of the theory of ionization, metals is regrouped, and no resemblance to the classical there soon developed a beautiful bit of theory to ex- scheme is shown. Each of these methods has some plain the solubility or insolubility of certain of the advantage, as well as some disadvantage, but the compounds, which are the basis of qualitative analysis. one disadvantage which is never present is the fact And so the theoretical background has finally been that with each scheme all of the necessary theory of precipitation, solution, and so forth, can be developed. developed. However, I am forced hy the present state of our As long as we have compounds in schematic analysis, theory and practice to remind you that the great bulk we will have the solubility product principle, complex of the data on which this beautiful theory is based has compounds, and all the theories which attend them. Would it not be more advantageous to return qualitabeen determined for single precipitations from pure solutions in which ionic concentrations must he deftly tive analysis to the realm of the laboratory where com; and accurately controlled, but which is impossible in pounds and equations are studied, and put less stress on the theory of it? If the theory is necessary, why many cases when foreign ions are present. The hydrogen sulfide scheme methods require close not let it be developed in physical chemistry or even in a course in stoichiometry? Then these mathematiSAYERS, R. R., N. A. C. SMITH, et al., "Investigation of toxic cal transformations need not clutter up the experigases from Mexican and other high-sulfur petroleums and pradmental chemistry of the qualitative laboratory. ucts." Bureau of Mines Bulletin 231, 1925, pp. 73 seq.
With this introduction I now submit for consideration a method of qualitative analysis without hydrogen sulfide. This method has received considerable attention in various laboratories and has been found entirely satisfactory for introductory work in the subject.%
When the residue is known to be free from PbC12, pour 5 to 10 cc. of NH40H over it. Black residue on filter paper: Hg. Acidify (litmus paper) the clear filtrate with HNOs. Whiteprecipitate: AgC1.
TABLE 1
Procedure 4. Precifi'iution of Group 11.-The filtrate from Group I (from P. 1) should be evaporated to 30 cc., if i t is larger in volume. Add 3 cc. of 2 Has04 and 30 cc. of ethyl alcohol and stir well. Filter. Resi-
GENERAL SCHEME OF ANALYSISBY GROUPS Test original material for Gmup VI (P. 40)
The solution may contain all the common bade a in slight excess and fllter
~~~~titumts. Add H
I 2rrmps 11. 111, IV, V. tter (P. 4)
FillroU warm an6 PrrciPilak:
Add HISO' and alcohol;
Fillrole: Groupa 111, IV, V. (Test 15 ee. of t h e Group I1 filtrate for Na+ and K+, bby Group VI.) (P. 41-42) To remainder add KOH in excess; then bail, and add NnrO, and boil. Filter (P. 13) Filtola: P r r ~ i 9 i l a U : Groups IV, V. Dissolve in HNOI HCI; KzSn01 KAlOt neutralize by (NHdrCOri add KSbOs NH4OH and (NHdaHPO.. Filter (P. 24) KaznOI KzCrO* Prcdpilote: FilLmir: KaAeO. MnN&POa Complex amGrow 111 pepo, monium salts (P. 13-23) B~PO. of Cu, Hg, Co. MgNHaPO, Ni. Cd Group I V Group V (P.24-31) (P. 32-38)
Bas04 srso.
case, PbSO. Gmup I1 (P.4-12)
+
GROUP I
Procedure 1. Precipitation of Group I.-To the cold solution (30 cc. in volume) contained in a beaker add 6 N HCl, drop by drop, and continue adding this acid nntil the precipitation is complete. Filter and wash three or four times with N HC1, catching the washings in the same vessel with the filtrate. Treat TABLE 2 ANuysrs OF GROUPI (P. 1TO P. 3) Preci9ilolr: AgCI. PbCla, HgaCIz. Extract with boiling PillroU: PhCI.. Add Residze: AgCI, HgaCh. ISCrrO? to precipitate yel- N&OH (P.3) low PbCrO. (P.2) Fiilmir: Ag(NH&Cl.
I
GROUP I1
Add dilute HNOI in excess to precipitate white AgW (P. 3)
II
water (P. 2) Extract with
fisidrr: Black HgNHCI Hg (P. 3)
+
white precipitate (Group I AgCl, PbClz, HgnCl*) by P. 2. Treat filtrate (Groups 11, 111, IV, V) by P. 4. If no precipitate forms, treat the solution by P. 4. Procedure 2. Extraction and detection of leadPour 10 cc. of boiling water over the residue from P. 1 on the filter paper. As this liquid runs through, catch .it in a test-tube and divide into two portions. To one portion add 1 cc. of HNOs and 2 cc. of 3 N KICIZO~. Yellow precipitate: PbCrO4. To the other portion add 1 cc. of HzSOr. White precipitate: PbSOd. If no precipitates form, then PbClz was absent in the Group I residue. Procedure 3. Detection of silner and mercury.If lead chloride is present in the residue (P. 2), continue to wash it with 10-cc. portions of boiling water, allowing each portion to run through the filter before adding the next; when a 10-cc. portion gives no reaction with KnCr04or with HzSOa, the residue is free from PbCl*.
-
a MUNRO, L. A., Can. Chem. Met., 17 (Dec., 1933); J. CAEM. Eonc., 11, 242 (1934); Cf. BROCKMAN, C. J., "Qualitative Analysis," Ginn and Co., Boston, Massachusetts, 1930.
TABLE 3 ANALYSISOF GROWI1 (P. 4 TO P. 12) Residue from ireolmcd with H d O . and alcohol ( P . 4): BaSO., PbSOd, CaSO,, SrSOa. Boil (P. 5) with 4 N NmCOa, filter, dissolve residue (P. 6 ) in HNOI, and filter; neutralize by NaOH, acidify with HCIHBOZ, add K r ,Ln. "..A ax*--
-.-.,-"-" ....
Residue: BaCrO, and PbCfi. T r e n t with NaOH; filter (P.7) R m i d u : BsCrO,
(P.8)
PilDalc: C a t + and Srt+. M a k e ammooiacal and add KPe(CN)e; filter (P. 10) F i l l :P b . Reridxr: CnKr P i 1 lr n t r: Add HC8H.G fa Fe(CN)a (P. 10) Srf +. Add mnfirm PbCr01 (NHhSO&to precipitate (P. 9) srso. (P. 11 and P. 12)
due: Group 11, by P. 5. Filtrate by P. 13 for Groups 111, IV, V. Wash twice on the filter paper with a 1:l solution of alcohol and water. Procedure 5. Treatment of the insoluble sulfate precifidate.-Transfer the residue from P. 4 to a beaker or large evaporating dish and boil with 50 cc. of 4 N NanCOa; filter and discard the filtrate. Transfer the residue to a beaker and boil with another 50 cc. of 4 N NaCOa; filter and discard the filtrate. Procedure 6. Separation of B a and Pb from Ca and Sr.-Dissolve the residue (from P. 5) in a very little warm dilute nitric acid; just neutralize the excess of free acid with NaOH, acidify with acetic acid, and add 1 g. of solid sodium acetate. Add a few drops of N KzCr04 solntion until the precipitation is complete. Filter and wash the residue with hot water. Yellow precipitate: BaCr01 and PbCrOa, by P. 7. Filtrate: Sr++and Ca++,by P. 10. Procedure 7. Separation of barium from lead.If the residue from P. 6 is large, transfer i t to a 30-cc. test-tube and add 5 cc. of 4 N NaOH, shake well, and filter. Residue: BaCrOl, by P. 8. Filtrate: NaHPbOz, by P. 9. Procedure 8. Con$rmtwn of barium.-The flame test gives a green coloration. Procedure 9. ConfLrmation of lead.-To the liltrate from P. 7 in a test-tube add acetic acid until the solution has an acid reaction (litmus). If lead ions are present a yellow precipitate of PbCr04will be formed. Procedure 10. Separation of calcium from strontium. -Make the filtrate, from P. 6 reserved above, ammoniacal by the addition of concentrated NHIOH, heat to boiling, and add 20 cc. of a concentrated solution of &Fe(CN)a, and heat again. Filter. Residue: Caby P. ll. KzFe(CN)s. Filtrate: sf+, Procedure 11. Precipitation of strontium.-Add a solution of ammonium sulfate to the filtrate from P.
10. A white precipitate indicates the presence of SrS04. Filter and confirm by P. 12. I Procedure 12. Confirmation of strontium.-Moisten a 'clean platinum wire in concentrated HCl and touch it to the precipitate obtained in P. 11; make a flame test for Srff. GROUP III
Procedure 13. Separation of Group III.-Make the filtrate from P. 4 (not over 100 cc. in volume), contained in a porcelain dish, alkaline with an excess of 6 N KOH, boil to evolve all the free NHa and to eliminate the excess of alcohol. Add 15 cc. of 6 N KzCOj solution and boil a t least five minutes, adding small amounts of NaOz from time to time, to completely oxidize the
add a Zn strip to completely remove all the Sn in the form of the metal. When all the Sn has been displaced, filter, and to the clear liltrate add NH4Cl and an excess of NH40H. Feathery white precipitate is Al(OH)r; filter and confirm the presence of Al(OH)a by P. 18. Procedure 18. Confirmation of aluminum.-Dissolve the precipitate obtained in P. 17 in 5 cc. of 3 N NH4GHsOz and 5 cc. of a 0.1 per cent. solution of aluminon. Mix thoroughly and let stand for a few minutes. Make this solution alkaline with NH*OH containing (NH4)zCOa. A bright red precipitate persisting in an alkaline solution indicates the presence of aluminum ions. the Procedure 19. Separation of antimony.-Use filtrate from P. 15. Divideit into two parts; one part
TABLE 4 ANALYSIS OP GROUP I11 (P. 13 TO P. 23) Fillrolc from lraolmcnl (P.13) wilh KOB. K.CO8, No,&: KAIO,. Ks6nOz. KIC~OLKSb03, KIASOC and NazCOs; boil and filter (P. 14) Residue: AI(0H)r. HSbOa. Sn(0H)r. Zn(0H)z. Dissolve in HCI: add N&Cl and NH.OH: boil andl a1ts (P. 15) Reddue: AI(OH)z, Sn(0H)a. Dissolve in HCI; divide into two Darts
solution; about 2 g. of NazOnwill suffice. Now add an equal volume of water, cool, and filter. Wash the residue with boiling water. Residue: Groups IV and V, by P. 24. Filtrate: Group 111,by P. 14. Procedure 14. Separation of Al, Sb, Sn, Zn.-Neutralize the filtrate from P. 13with HCl until any precipitate which may form in the solution just redissolves. Add a slight excess of solid NazC03 and boil for a few minutes. Filter and wash the residue with water. Residue: Al(0H)o Sn(OH)4, Z~(OH)Z,HSbOs, by P. 15. Filtrate: As04=, CrOr, by P. 22 and P. 23. Procedure 15. Separation of A1(OH)3and Sn(OH)4.Transfer the residue from P. 14 to a beaker or a dish, dissolve in a little hot dilute HCl, add 1to 2 g. of solid N H Q then make ammoniacal with NH40H, boil and filter, wash the residue with hot water. Residue: Al(OH)& Sn(OH)&, by P. 16. Filtrate: NHBbOa, (NH&ZnOz, by P. 19 and P. 21. Procedure 16. Separation and confirmation of Sn.Dissolve the residue from P. 15 in HC1 and divide this solution into two parts. Test one part by P. 17 for Al+++. To the other part add an iron nail, or powdered iron, warm, and let stand for ten minutes, then filter into a saturated solution of HgCla. White precipitate turninggray is HgCl or Hg, which indicates the presence of Sn++. Procedure 17. Separation of aluminum.-To one part of the solution obtained in P. 16, if SnCf is present,
KsSnOa.
Neutralize by HNOa; add excess solid
FiBmle:
KCrO,.
&A
$04.
Divide into two
Part 2. AsO.: Acidify with strong HNOI; add equal volume of (NH.)SMOOG warm. Yellow precipitate iodieatcs As0.(P. 23)
for the antimony test, the other for the zinc test by P. 21. To the part to be tested for Sb add 5 cc. of HC1, or as much as is required to definitely acidify it, and an iron nail. Warm and let stand for ten minutes. Feathery black incrustations on the nail indicate the presence of metallic Sb. Residue: Sb, by P. 20. Filter and wash once with water and remove the incrustations from the nail. Procedure 20. Confirmation of antimony.-Pick out the nail and scrape off as much of the Sb as possible. Dissolve this Sb in FeCls and HC1 with boiling; to the resulting solution add NazSzOaand boil again. Red precipitate is Sb20S2. Procedure 21. Sefiaration and confirmation of zinc.To the ammoniacal solution reserved in P. 19 add a solution of &[Fe(CN)s]. White precipitate indicates the presence of Zn ions. Procedure 22. Confirmation of chromium.-The liltrate from P. 14 will be distinctly yellow-colored if the CrOh is present. To about 10 cc. of this solution add a few drops of HNOs to acidify; cool thoroughly, add 1 cc. of ether and one drop of three per cent. HzOz, and shake. A blue color in the ether layer coniirms the presence of Cr04-. the reProcedure 23. Detection of arsenic.-To mainder of the filtrate from P. 14 add strong HNO, to acidify it, then add 15 cc. of a solution of (NH4)~MoO4, and heat to boiling. Yellow precipitate, rather
slow to form, indicates the presence of the As04- ion. GROUP N
Procedure 24. Separation of Groups I V and V.Dissolve the residue containing Groups IV and V (from P. 13) in hot 6 N HNOa, using as little as possible to get complete solution; if necessary, add a few drops of a twenty per cent. solution of NaNOz and boil. Nearly neutralize this solution with solid (NH4)zCOa until any precipitate which forms just redissolves, then pour into an equal volume of warm concentrated NH40H with continuous and vigorous stirring. Add TABLE 5
GROUP IV (P. 24 TO P. 31) P m N i l o ir ~ the ~~OIYOCCS of MI, PI, B;, Mz. Dissolve in eoncentrated HNO. + N a N a . Boil and add solid Kcla. Dilute and filter (P.25) Pillrolc: Bi+++. Fe+++. Mg++. Add eleePa R3sidnr: MnO,. ANALYSISOP
Identify by bead (P.25 and P. 26)
test
NHgOH and N-Cl, boil and filter (P.27) ~ ~ r i d u r : B~(oH), and ~ e - ~ i i t o i r :~ g + + . (OH): Dissolve io H a ; divide Add excess of Nnrrolutton into two parts HPO., boil to w e part 2. ~ d dcipitate MgNHapart 1. ('. 31) &Fe(CN)e. NaBaOa and Blue precipi- boil to precipitate test for tatebl=ckBi& iron Fea(Fe- (P. 28 and P. (CN)dr (P.30) 29)
10 cc. of a N solution of (NH4)2HP0. Filter by decantation and wash the residue with hot two per cent. NH40H (one part of dilute NH40H to four parts &O). Residue: Group IV, by P. 25. Filtrate: Group V, by P. 32. Procedure 25. Detection and separation of manganese.-In a porcelain dish boil the residue (from P. 24) in a small volume of concentrated HNOa, with the addition of a twenty per cent. solution of NaNOz, drop by drop, until the residue is entirely dissolved, then continue to boil until all the red fumes are gone, and until the volume is 10 to 15 cc. To this con-
contained on a small watch glass and heat again. Green or bluish green head indicates NazMn04. Procedure 27. SeNration of bismuth and iron.Add a few drops of a solution of potassium sulfate to the filtrate from P. 25. Any precipitate will be the sulfates of Ca, ST, Ba, or Ph, and must be filtered and analyzed according to the scheme for Group 11. To the filtrate from this sulfate precipitate add an excess of NH40H and 1 g. of solid NHICI. Filter any precipitate which forms and wash it with boiling water. Residue: Bi(OH)s and Fe(OH)* by P. 28. Filtrate: Mg++, by P. 31. Procedure 28. Separation of bismuth.-Dissolve the residue from P. 27 in as little HCl as is required. Divide the solution into two parts; use one part for the detection of Fe hy P. 30. To the other part add 3 cc. of HCl, 1 g. of solid Na&Oa, and boil until the precipitate coagulates. Black precipitate: BizSa. Filter and wash with water, and confirm by P. 29. the Procedure 29. Confirmation of bismuth.-Boil residue from P. 28 in a little concentrated HNOa until even the free sulfur has been dissolved, or a t least is clear yellow in color. Add an excess of NHaOH and filter. Treat the residue on the paper with 5 cc. of hoiling freshly prepared sodium stannite solution. Black residue indicates Bi. Procedure 30. Confirmation of iron.-To the HCI solution reserved in P. 28 a d d a few drops of potassium ferrocyanide solution. Blue precipitate: presence of iron. Procedure 31. Confirmation of magnesium.-To the ammoniacal filtrate from P. 27 add an excess of disodium phosphate solution. A white crystalline precipitate (MgNHdP04) indicates the presence of Mg++. The precipitate should be soluble in HC2H302. To the acetic acid solution add 0.2 cc. of Titan yellow, then a
TABLE 6 (P. 32 TO P. 39)
ANALYSIS021 GROWV
F i l ~ r o ki s m i d o n of phorphole of Hz++.Cut+, Cd++, Cot+, N i i + in NHaO.4: Acidify with HCI, bail with Na2ssOa, filter through a double filter, wash (P ,321 Pillmlc: Co++, Cdt*, Niif. Make ammoni-I, then acid by HC.HZO;, divide into Rrriduc: HgS, CuS. Wash, boil with HNOI, filter (P.33) two parts (P.38) -. Part 1. Test Ca+*. Add Farl 2. Test for N i t + and Cdit. Add dimethylILr;duc: HgS. Dissolve in Fillrole: Cut+. Add NHIglyorime and NHaOH, warm, and filter (P. 37) confirm with SnCb OH, then acidify with HCg- KNO, and let stand (P. 36). HIOI, add K.Pe(CN)a (P.35) Optional: Test with a-nitroso(P. 34) 8-naphthol glyoxime excer. NHACI, NSOH, and H~OI,l a a m , end pour into equal volume of NH'CIQI (P.38 and P. 39)
centrated hoiling solution add in small portions from time to time, with stirring, a total of 1 g. of solid KCIOJ, continuing gentle boiling for two to three minutes. Cool, dilute with 10 cc. of cold water, and filter. Residue: Mn02, by P. 26. Filtrate: Fe+++, Bi+++, by P. 27. Procedure 26. Confirmation of manganese.-On a sodium carbonate bead take up a very small amount of the precipitate obtained in P. 25 and heat. While still hot dip the bead into a little powdered KC103
slight excess of 4 N NaOH. A red flocculent precipitate confirms the presence of Mg(0H)z. GROUP V
Procedure 32. Separation of mercury and cop@?Acidify (litmus) the filtrate from P. 24 with HC1, add 1 g. of solid Na2S80a,and boil for several minutes; filter and wash the residue once with water. Residue: HgS and CuS, by P. 33. Filtrate: Cd++, Co++, ~ i + +by , P. 36.
Procedure 33. Separation of mercury.-Boil the residue from P. 32 with 10 cc. of dilute HNOa, filter, and wash the residue with water. Black residue: HgS, confirm by P. 34. Filtrate: CuCC,by P. 35. Procedure 34. Confirmation of mercury.-Dissolve the residue from P. 33 in aqua regia, about 10 cc. of the mixed acids, boil the resulting solution free from excess oxidant and filter into a solution of SnC12. White or grayish precipitate is HgCl or Hg. Procedure 35. Confirmation of copper.-If the filtrate from P. 33 is blue, copper is indicated. Make the solution ammoniacal to get an intense blue coloration if copper ions are present. Acidify the solution with HCeH30z and add a solution of G[Fe(CN)s] to get a reddish coloration with traces of copper ions, or a red precipitate with larger quantities of copper. Procedure 36. Detection of co6alt.-To the iiltrate from P. 32 add NH40H in just a slight excess and filter any precipitate which forms (boiling may aid in coagulating the sulfur which may separate). Now acidify this solution with acetic acid and divide it into two parts: one for the detection of cobalt and one for the detection of nickel and cadmium, by P. 37. To the first part add an equal volume of potassium nitrite, warm, and let stand for a few minutes. Yellow precipitate indicates the presence of R ~ C O ( N O ~ An )~. optional method involves the use of the a-nitroso-p naphthol test. Procedure 37. Detection and confirmation of nickel.-To the second part of the solution which was reserved in P. 36 add a solution of dimethylglyoxime uutii an excess is present and then add a slight excess of NHIOH, boil to coagulate the precipitate and make it crystalline. Filter. Filtrate: test for Cdff, by P. 38. Procedure 38. Detection of cadmium.-To the filtrate from P. 37 add 2 g. of NH4Cl, then NH4OH and a few cubic centimeters of three per cent. HIOz and warm. Pour this solution into an equal volume of twenty per cent. NH4C104 in NH40H. White precipitate is Cd(C104).4NH3. Confum by P. 39. Procedure 39. Confirmation of cadmium.-Filter the
precipitate of Cd(C104)n.4NHaobtained in P. 38 and wash it with ten per cent. NH40H. Dissolve it into 2 cc. of dilute HC1, add an excess of NH40H and then 3 cc. of thirty per cent. KI solution. A white precipitate is Cd(NH&. GROUP VI
Procedure 48. Detection of ammonium.-To a portion of the original solid material or solution add an excess of 6 N NaOH and boil gently; immediately test the gas which is evolved with moist red litmus paper. If the paper turns blue in color, ammonium salts are present. Procedure 41. Detection of sodium.-To 5 cc. of the original material add sufficient KOH solution to insure complete precipitation and then filter. Make the TABLE 7 ANALYSISOP GROW VI N&+: To 5 ec. of the original material add an excess of NaOH solution, warm. and rest the fumes for N& (P.40) For N o i ; To 5 ee. of the original material add a slight eras. of KOH solution .., (free from Nn+) and filter. Makes flame tent for N a with the filtrate For
.-
\ Y . 411
F a Kt: To 5 ee. of the original rnatuial add a slight excess of NnOH solution (free from K+) and filter.
M a k e a flame test for K + with the filtrate
(P.42)
filtrate slightly acid with concentrated hydrochloric acid and then moisten a piece of clean platinum wire with this solution and heat in the hottest part of the non-luminous Bunsen flame. A yellow flame coloration which persists for more than five seconds indicates more than traces of sodium. Procedure 42. Detection of potassium-To 5 cc. of the original material add sufficient NaOH solution to insure complete precipitation and then filter. Make the filtrate slightly acid with concentrated hydrochloric acid and then moisten a piece of clean platinum wire with this solution and heat in the hottest part of the non-luminous Bunsen flame. A violet-colored flame, visible through a good piece of cobalt glass. indicates the presence of a potassium salt.
