IC-NRLF SB 27fi 072 GIFT OF PROF. w.B. AN OUTLINE OF QUALITATIVE ANALYSIS, FOR BEGINNERS, BY JOHN T. STODDARD, PH. D., PROFESSOR OF CHEMISTRY IN SMITH COLLEGE. (|team ^te^ o^ ^a^et-tc H^int 1883. Copyright by JOHN T. STODDARD. PREFACE, The desire to place in the hands of my students who are beginning the study of Qualitative Analysis a clear, concise, and simple Outline of the subject, has led me to the prepara- tion of this little work. Much that is found even in elementary books is purposely omitted in this. Manipulation can only be satisfactorily learned from practical demonstration. Writing of equations and drawing up of analytical tables are valuable exercises for the student. Hence the little book presents only an OUTLINE, which is to be filled in by the student with the teacher's assis- tance. The method which its arrangement suggests has been chosen as the one best calculated to give the student an intelligent grasp of the subject, and help him to become more than a mere analytical machine. The student is expected to make all the reactions and ex- press them in written equations. When this has been done for the members of a group of metals, a few solutions, each containing one or more members of the group, are given and analyzed according to the directions. The exercises on the group are|]then to be worked out. When each of the groups 237339 IV PREFACE. has thus been thoroughly studied, a number of solids and so- lutions are given for systematic examination for all the groups. These are at first of the simplest composition, and increase gradually in complexity and analytical difficulty. The detection of acids is now taken up in the same way, except that an examination for metals, of course, always pre- ceeds that for the acids. Finally, a large variety of substances is given for complete analysis. J. T. s. Smith College Laboratory. Dec. 25,. 1882. UN iv o I. DETECT IOJST OF THE METALS. SECTION I. GROUPING OF THE METALS. Group I. Metals which are precipitated as chlo- rides by HC1 : Silver and Mercury (ous) completely,. Lead incompletely, Group II. Metals not falling under Group I, which are precipitated as sulphides from acid (HC1) solution by H 2 S : Sub-group A: Sulphides insoluble in (NH 4 ) 2 S : Mercury (ic), Lead, Bismuth, Copper, Cadmium. Sub-group B : Sulphides soluble in (NH 4 ) 2 S : Tin, Antimony, Arsenic, Gold, Platinum. Group III. Metals not falling under Groups I and II, which are precipitated as hydroxides bv NH 4 OH in the presence of NH A C1 : Iron, Chro- mium, Aluminium. '.ANALYSIS. Group IT. Metals not falling under Groups I-III, which are precipitated as Sulphides by (NH 4 ) 2 S : Nickel, Cobalt, Manganese, Zinc. Group Y. Metals not falling under Groups I-IV, which are precipitated as Carbonates by (NH 4 ) 2 C0 3 : Barium, Strontium, Calcium. Group VI. Metals not falling under Groups I-V and having no common precipitant : Magnesium, Potassium, Sodium, Ammonium. SECTION II. REACTIONS OF METALS AND ANALYSIS OF GROUPS. Group I. REACTIONS. Silver. Ag 1 . Solution for reactions, AgN0 3 . HC1 precipitates white curdy AgCl; soluble in and in KON ; reprecipitated by HN0 3 ; darkens on exposure to light. 2. H 2 S or (NH^jjS precipitates black Ag a S ; solu- ble in boiling HN0 3 . 3. NH 4 OH precipitates from neutral solution only brown Ag 3 ; readily soluble in excess of 4. NaOH precipitates brown Ag 2 0. 5. K 2 Cr0 4 precipitates dark red Ag 2 Cr0 4 ; soluble in HN0 3 or in NH 4 OH. 6. KI precipitates yellowish Agl. 7. Na 2 HP0 4 precipitates yellow Ag 3 P0 4 . 8. Cu and some other metals precipitate metal- lic Ag. 9. (a) Heated with Na 2 C0 3 on charcoal before the, blowpipe, solid compounds of silver yield bright, malleable globules of Ag, (b) which are soluble in HN0 3 . Characteristic Reaction, L QUALITATIVE ANALYSIS. Lead. Pb". Solution for reactions, Pb2N0 3 . 10. HC1 precipitates (incompletely) white PbCl 2 ; soluble in boiling H 2 0, and crystallizes from this so- lution on cooling ; converted by NH 4 OH into white Pb.CtiEfoCl, which is insoluble in H 2 0. 11. H 2 S or (NH 4 ) 2 S precipitates black PbS ; solu- ble in hot HN0 3 . 12. NH 4 OH precipitates a white basic salt. 13. NaOH precipitates white Pb(OH) 2 ; soluble in excess. n.4j)K 2 Cr0 4 precipitates "chrome-yellow" PbCr0 4 ; soluble in NaOIi ; soluble with difficulty in UNO,. (L5J KI precipitates bright yellow PbI 2 ; soluble in boiling H 2 0, and crystallizes from this solution, on cooling, in golden scales. J (16) H 2 S0 4 precipitates white PbS0 4 ; soluble jn ammonium tartrate or NaOLL 17. Zn precipitates metallic Pb in crystalline form. 18. Compounds of Pb, heated with Na 2 C0 3 on charcoal, yield soft, malleable, and easily fusible globules of Pb, and a yellow incrustation of PbO on the charcoal. The globules are soluble in IIN0 3 . Characteristic Reactions, 14, 15, 16. Mercury. Hg". Mercurou* flalfa. Solution for reactions, Hg 2 2N0 3 . 1Q. HC1 precipitates white Hg a Cl 8 (calomel) ; con- verted by NH 4 OH into black NH 2 LIg 2 Cl. 20. H 2 S or (N1I 4 ) 2 S precipitates black fIg 2 S ; in- soluble in hot HNO 8 . ^1. NH 4 OH precipitates black NII 2 Ug 2 N0 3 . GROUP I ; ANALYSIS. 5 22. NaOH precipitates black Hg 2 ; decomposes readily into HgO and Hg. 23. K 2 Cr0 4 precipitates dark red basic chromate ; soluble with difficulty in HN0 3 . 24. KI precipitates yellowish-green Hg 3 I 2 . 25. SnCl 2 precipitates grey Hg. 26. Cu and some other metals precipitate metal- lic Hg. 27. Compounds of Hg yield the metal readily when heated with Na 2 C0 3 in a small tube. Hg is volatile and condenses on the cooler parts of the tube ; soluble in HN0 3 . Characteristic Reactions, 19, 27. ANALYSIS. (a) Add HC1 until no further precipitation occurs; filter and wash with cold water. The filtrate may contain Groups II-VI. The white precipitate con- .sists of one or more of the chlorides of Group I : AgCl, PbCli, Hg 2 Cl 2 . (b) Add boiling H 2 to the precipitate on the fil- ter (cf.10). Test the filtrate for Pb by 10 and 14. If Pb is found, the precipitate is washed repeatedly with hot water until free from it. A residue insoluble in hot water indicates AgCl, Hg 2 Cl 2 , or both. (c) Add NII.OH ; Hg 2 Cl 2 is blackened (cf. 19), while AgCl is dissolved (cf. 1), and its presence proved by adding HN0 3 . The black residue containing Hg is tested by 27. 6 QUALITATIVE AXALYSIS. EXERCISES. I. Draw up a table for the analysis of this group. II. Devise another method for the analysis of a solution containing the members of this group. III. if PbCl 2 is not completely removed from the precipitate before adding NH 4 OH, how is it affected by this reagent ? IV. Give the important compounds of the members of this group ? Describe their appearance and uses. Grl-Ollp IJ. SUB-GKOUP A. Hg, Pb, Bi, Cu antt Cd. REACTIONS. i Mercury. Hg". Mercuric Salts. Solution for rejections, HgCl 2 . H 8 S, added by degrees, produces, first, a white precipitate, which changes to orange, brownish red, and finally to black HgS. This is insoluble in hot HN0 3 ; soluble in aqua regia. 29. NH 4 OH precipitates "white precipitate," NH 2 HgCl. 30. NaOH precipitates yellow HgO. 31. K 2 CrO 4 precipitates an orange basic chrumate; readily soluble in HN0 3 . 32. KI precipitates yellow HgI 2 , which rapidly be- comes scarlet. / (3) SnCl 2 precipitates white Hg 2 Cl 2 ; if added in excess, grey metallic Hg. GROUP II. A ; REACTIONS. 7 34. Reactions 26 and 27 for raercurons salts. Characteristic Reactions, 28 and 33. Lead. Pb". PbS is precipitated by H 2 S even from solutions of PbCl 2 ; so that lead belongs to both the first and second groups. Of. reactions, 10-18. Bismuth. Bi m . Solution for reactions, BiCl 3 . 35. H 2 S precipitates black Bi 2 S 3 ; soluble in HN0 3 . 36. NH 4 OH precipitates white BiO.Oli ; becomes yellow Bi 2 3 on boiling. 37. NaOH precipitates same. 38. K 2 Cr0 4 precipitates yellow Bi 2 3Cr0 4 ; soluble in HN0 3 ; insoluble in NaOH. 39. Zn or Fe precipitates spongy Bi. SO 4 , white aii-d heavy ; Sulphur, light and floating. Dissolve HgS in aqua regia, expel excess of acid, and test with SnCl 2 (cf. 33), (g) Infiltrate may contain Pb, Bi, Cu, Ud. Add H 2 S0 4 and filter if necessary. Al White precipitate, PbS0 4 . Dissolve in and test by 14. (h) The -filtrate may contain Bi, On, Cd. Add NH 4 OH and filter if necessary. White precipitate. Dissolve in a little cone. HC1 ; expel excess of acid and pour into H 2 (cf. 40). (i) Filtrate may contain Cu, Cd. If blue, Cu is present. Add KCN until the solution becomes color- *In the absence of Sub-group B, omit this step and treat at once with HNO 3 as below (e). 2 10 QUALITATIVE ANALYSIS. less. Treat warmed solution with H 2 S (avoid excess), yellow precipitate is CdS (cf. 53). If not blue, Cd alone can be present. Treat with H 2 S. EXERCISES. V. Draw up a table for the analysis of this group. VI. Why is the solution which is to be examined for Group II evaporated with HC1 before treatment with H 2 S (see a) ? VII. Why is it important to wash the precipitated sulphides free from HC1 (see c) ? VIII. Explain the presence of S and that of PbS0 4 in the residue insoluble in HNO 3 (see f). IX. If the nitrate from HgS (see g) were treated at once with NH 4 OH, what would the precipitate con- tain, and how could it be examined ? X. How may the color of the H 2 S precipitate in- dicate the presence or absence of certain members of this group ? XI. Give the important compounds of the mem- bers of this group ; their appearance and uses. SUB-GROUP B : Sn, Sb and As. REACTIONS. Tin. a. Sn 11 . Stannous Salts. Solution for re- actions, SnCl 2 . 56. H 2 S precipitates dark brown SnS ; soluble in yellow (N"H 4 ) 2 S 2 ; reprecipitated as yellow SnS 2 by HC1. 57. NII 4 OH precipitates white Sn(OH) 2 . 58. NaOH precipitates same ; soluble in excess. 59. HgCl 2 precipitates white Hg 2 Cl 2 (cf. 33). 60. Zn precipitates metallic Sn. GROUP II. B; REACTIONS. 11 61. Heated on charcoal with Na 2 C0 3 and borax, compounds of Sn yield white, malleable globules ; in the oxidizing flame, slight white incrustation of Sn0 2 . Sn is soluble in cone. HC1 ; is converted by cone. HN0 3 into insoluble metastannic acid. 62. Stannous salts are converted into stannic by oxidizing agents : HN0 3 , 01, Fe 2 Cl 6 , etc. b. Sn iv . Stannic Halts. Solution for reactions, SnCl 4 . 63. H 2 S precipitates yellow SnS 2 ; soluble in (NH,) 2 8, in NaOH, and in hot cone. HC1. 64. NH.OH precipitates white SnO(OH) 2 . 65. NaOH precipitates the same; soluble hi excess. 66. Reactions 60 and 61. Characteristic Reactions ; a. 56, 59 ; b. 63. Antimony. Sb m . Solution for reactions, Sb01 3 . 67. H 2 S precipitates orange Sb 2 S 3 ; soluble in (NH 4 ) 2 S, NaOH, and in hot cone. HC1. 68. NH 4 OH precipitates white Sb(OH) 8 . 69. NaOH precipitates same ; soluble in excess. 70. H 2 precipitates from SbCl 3 , white SbO.Cl ; soluble in tartaric acid. Cf. 40. 71. Zn in presence of of HC1 and Ft, precipitates Sb as a black powder, adhering to the Pt. The black stain on the Pt is not removed by HC1 ; but warm, cone. HN0 3 causes the stain to disappear by convert- ing Sb into HSb0 3 . 72. Heated on charcoal with Na 2 C0 3 , compounds of Sb yield a white incrustation of Sb 2 3 and hard brittle globules of Sb, which are insoluble in HC1 ; oxidized by HN0 3 ; dissolved by aqua regia. 12 QUALITATIVE ANALYSIS. Arsenic, a. As 111 . Arsenious Compound*. So- lutions for reactions, Na 8 As0 8 . 73. H 2 S precipitates yellow As 2 S 3 ; soluble in (NH 4 ) 2 S and in NaOH ; reprecipitated by HC1 ; nearly insoluble in cone. HC1. Cf. 63 and 67. 74. NH 4 OH and NaOH produce no precipitates. 75. AgN0 3 added to a neutral solution of an ar- senite precipitates yellow Ag 3 As0 3 . 76. CuS0 4 added to a neutral solution of an urso nite, precipitates CuHAs0 3 , " Scheele's green." 77. Cu added to an HC1 solution of arsenic be- comes coated with a grey film of metallic As. Reinscli's test. 78. Arsenious compounds are converted by oxidiz- ing agents into arsenic compounds. The simulta- neous reduction of the oxidizing agent is shown in the following reactions : a. K 2 Cr0 4 warmed with arsenious compounds becomes green, c. KMn0 4 is decolorized. b. As v . Arsenic Compounds. Solution for reac- tions, Na s As0 4 . 79. H 2 S precipitates, in warm solutions free from HN0 3 , As a S 3 and S. Cf. 73. 80. Cf. 74. 81. AgN"0 3 , added to a neutral solution of an arse- nate, precipitates reddish brown Ag 3 As0 4 . 82. MgS0 4 precipitates, in the presence of NH 4 OH and NH 4 C1, white crystalline MgNH 4 As0 4 . 83. Heated on charcoal with Na 2 C0 3 , all com- pounds of arsenic are reduced to As, which volatilizes with apharacteristic garlic odor. GROUP II. B ; ANALYSIS. 13 84. Heated with charcoal in a glass tube, a " mir- ror" of metallic arsenic is obtained. SUB-GROUP B ANALYSIS. (a) The sulphides SnS 2 , Sb 2 S 3 , As 2 S 3 , are precipita- ted from the filtrate from Sub-group A by adding HC1 to acid reaction. Filter and wash with hot H 2 0. Boil with cone. HOI and filter. (b) The residue, light yellow As 2 S 8 , is converted into a soluble arsenate by boiling with cone. HC1 and a few crystals of KC10 3 . Test by 82. (c) The filtrate may contain Sn and Sb. Add Zn and platinum foil to the acid solution. Both metals, if present, are reduced to the metallic state, Sn be- ing deposited on the Zn, and Sb as a black stain on the Pt. Remove excess of Zn, wash, add cone. HC1, warm to dissolve Sn, and filter. (d) Residue is black ; Sb ; remove as far as possible from the Pt ; dissolve in aqua regia and expel excess of acid, dilute and test with H 2 S. (e) Solution may contain Sn ; expel excess of acid, dilute and test with Hg01 2 . Au and Pt belong to this Sub-group and in the course of analysis their sulphides, Au 2 S 3 and PtS 2 , being insoluble in HC1, remain in the residue with As 2 S 3 (see b). By treatment with HC1 and KC10 3 , they are dissolved and detected by the following special tests : Gold. Au m 85. SriCl 2 +SnCl 4 produce a purplish coloration or precipitate ; " Purple of Cassius." 14 QUALITATIVE ANALYSIS. Platinum. Pt IV 86. NH 4 C1 precipitates yellow crystalline 2NH 4 C1, PtCL ; less soluble in alcohol than in H 2 0. EXERCISES. XII. Draw up a table for the analysis of this group. XIII. Devise another way for the detection of the members of this group, if in solution by themselves. XIV. If H 2 S were added to a solution containing all the members of Groups I and II, what would occur ? XV. What is the action of KC10 3 in b ? XVI. Give the important compounds of the mem- bers of this group ; their appearance and uses. Group III. KEACTIONS. Iron. a. Fe". Ferrous Salts. Solution, FeCl 2 . 87. (NH 4 ) a S precipitates black FeS ; soluble in HC1. 88. NH 4 OH or NaOH precipitates white Fe(OH) 2 , which quickly acquires a dirty green color, and ulti- /ately becomes reddish brown Fe r (OH) . 89. (NH 4 ) 2 C0 3 or Na 2 C0 3 precipitates white FeCO^ which rapidly darkens in color. / 90. K 4 Fe(CN) 6 precipitates white K 2 Fe 2 (CN) 6 , which rapidly becomes blue. 91. K 3 Fe(CN) 6 precipitates " Turnbull's blue," Fe 3 Fe 2 (CN) 12 . I/ GROUP III ; REACTION'S. 15 92. KCNS produces no coloration. 93. Ferrous compounds are converted into ferric by oxidizing agents, such as (a)HN0 3 , (b)KC10 3 and HC1, (c)Cl. b. Fe iv . Ferric Salts. Solution, Fe 2 01 6 . 94. (NH 4 ) a S precipitates black FeS and S. 95. NH 4 OH, NaOH, (NH 4 ) 2 C0 3 , or Na 2 C0 3 pre- cipitates reddish brown Fe 2 (OH) 6 . 96. K 4 Fe(ON) 6 precipitates "Prussian blue," Fe 4 Fe 3 (CN) 18 . t/ 97. K 3 Fe(ON) G produces a reddish brown color. 98. KCNS produces an intense blood-red color. 99. Reducing agents, such as (a)H 2 S, (b)S0 2 , (c)Sn01 2 , (d)As 2 3 , convert ferric into ferrous com- pounds. 100. Compounds of Fe color the borax bead ; yel- lowish red in the oxidizing flame ; green in the re- ducing flame. 101. Heated on charcoal with Na 2 C0 3 , compounds of Fe yield magnetic particles, but no globule. Characteristic Reactions ; a. 91 ; b. 96 and 98. Chromium. Cr iv . a. Chromium Salts. Solu- tion, Cr 2 3S0 4 . 102. (NH 4 ) t 8 precipitates bluish green Cr 2 (OH) 6 ; soluble in acids. 103. NII 4 OH precipitates Cr 2 (OH) 6 . 104. NaOH precipitates Cr 2 (OH) 6 ; soluble in ex- cess ; reprecipitated by NH 4 C1 or by boiling. 105. The oxide and salts of chromium are con- verted into chromic acid, or chromates, by powerful 16 QUALITATIVE ANALYSIS. oxidizing agents ; e. g. fusion with Na 2 C0 3 and KN0 3 on platinum foil gives yellow K 2 Cr0 4 ; soluble in H 2 0. b. Chromic Acid. Solution, K 2 Cr0 4 . 106. Of. 5, 14, 23, 31, 38, 45, 52. 107. Acids convert yellow K 2 Cr0 4 into red K 2 O 2 7 ; alkalies produce the reverse reaction, and no precipitation. 108. Keducing agents (a)SO a , (b)H 2 S, (c) alco- hol convert solutions of chromates, to which HOI has been added, into green solutions of chrom- mium salts. 109. All compounds of chromium color the borax bead green. Characteristic ; color of solutions and bead, 105. Aluminium. A1 IV . Solution, A1 2 3S0 4 . 110. (NH 4 ) 2 S precipitates white flocculent A1 2 (OH) 6 ; soluble in acids. 111. NH 4 OH precipitates the same. 112. NaOH precipitates the same ; soluble in ex- cess ; reprecipitated by NH 4 C1. 113. Heated on charcoal, moistened with Co2N0 3 and heated again, compounds of Al yield an infusible blue mass. Characteristic Reactions ; 112, 113. ANALYSIS. (a) If the solution smells of H 2 S (as will be the case if it is the nitrate from Group II), boil until all traces of this gas are expelled. If a ferrous salt ANALYSIS. 17 (test a few drops by 91) is present, boil and add cone. HN0 3 , a few drops at a time, till it is completely converted into a ferric salt. If the solution contains neither H 2 S nor ferrous salts, begin at (b). (b) Add to the hot solution NH 4 C1 if the solu- tion is to be examined for the following groups, and a slight excess of NH 4 OH. Filter and wash with hot H 2 0. The filtrate may contain Groups IV-VI. The precipitate consists of one or more of the hy- droxides of Group III: Fe 2 (OH) 6 , Cr s (OH) 6 , A1 2 (OII) 6 . (c) Dissolve the precipitate in HC1, add excess of NaOH and boil a few minutes ; filter if necessary. (d) The precipitate ma} r contain Fe and Or. ^ Fuse on platinum foil with Na 2 C0 3 and KN0 8 ; boil the mass, when cool, with H 2 0, filter if necessary, boil the filtrate with acetic acid to expel C0 2 , and test for Or with PbAc 2 . Of. 14. A residue insoluble in H 2 is dissolved in HC1 and tested for Fe by 96 or 98. (e) The filtrate may contain Al ; acidify with HC1 and add 1S T H 4 OH. Of. 111. EXERCISES. XVII. Draw up a table for the analysis of this group. XVIII. Describe the important compounds of the members of this group and their uses. 18 QUALITATIVE ANALYSIS. Group IV. REACTIONS. Manganese. Mn IIandIV -. Solution, MnS0 4 . 114. (NH 4 ) 2 S precipitates flesh-colored MnS ; sol- uble in acids, even in acetic acid. 115. NH 4 OH precipitates (incompletely) whitish Mn(OH) 2 , which soon darkens in color. In the pres- ence of salts of ammonium this precipitate is not produced ; but the solution, on standing, soon be- comes cloudy, and ultimately all the Mn is precipita- ted as brown Mn 2 2 (OH) 2 . 116. NaOH precipitates Mn(OH) 2 . 117. Fused with Na 2 C0 2 and KN0 3 on platinum foil, all compounds of Mn yield bright green Na 2 - Mn0 4 ; soluble in cold H 2 0, decomposed by boiling. 118. Compounds of Mn color the borax bead ame- thyst in the oxidizing flame. Characteristic Reactions ; 114, 117, 118. Zinc. Zn". Solution, ZnS0 4 . 119. (NH 4 ) 2 S precipitates white ZuS ; soluble in HC1, but insoluble in acetic acid. 1*40. ^NH 4 OH or NaOH precipitates white gelati- nous Zn(OH), ; soluble in excess of either reagent ; reprecipitated from dilute solution by boiling, but not byNH 4 Cl. Of. 312. 121. Heated on charcoal with Na 2 C0 3 , compounds of Zn give an incrustation of ZnO, which is yellow while hot and white when cold. 122. Moistened with Co2N0 3 and strongly heated GROUP IV ; REACTIONS. 1& before the blowpipe, compounds of Zn yield an infus- ible green mass. Characteristic Eeactions ; 119. Cobalt. Co llandiv . Solution, Co2N0 3 . 123. (NH 4 ) 2 S precipitates black CoS ; insoluble in HC1 ; soluble in HN0 3 and in aqua regia. 124. NH 4 OH precipitates (incompletely) blue basic salts ; soluble in excess to a brownish red solution. Salts of ammonium prevent the precipitation. 125. NaOH precipitates the same ; converted by boiling into pale reddish Co(OH) 2 . If exposed to the air without boiling, the precipitate turns green. 126. KN0 2 added to cobalt solutions, which are strongly acid with acetic acid, precipitate, on stand- ing, a yellow crystalline double salt. . 127. KCN precipitates brownish white Co(CN) 2 ; soluble in excess and reprecipitated by HC1 or H 2 S0 4 . If to the solution in excess of KCN, a few drops of HC1 be added and the solution boiled for some time, 6KCN, Co 2 (CN) fi is formed, which is not precipitated by HOI or H 2 S0 4 , nor by NaClO. 128. Compounds of Co color the borax bead deep blue. Nickel. Ni llandiv . Solution, Ni2N0 3 . 129. (NH 4 ) 2 S precipitates black NiS, slightly sol- uble in excess, forming a brown solution, from which it is reprecipitated by boiling ; insoluble in HC1 ; soluble in HN0 3 or aqua regia. 130. NH 4 OH precipitates (incompletely) light green Ni(GH) 2 ; soluble in excess, yielding a blue 20 QUALITATIVE ANALYSIS. solution. Salts of ammonium prevent the precipita- tion. 131. NaOH precipitates the same. 132. KN0 2 in the presence of acetic acid produces 110 precipitate. 133. KON precipitates yellowish green Ni(CN) 2 ; soluble in excess and reprecipitated by HC1 or H 2 S0 4 , even after boiling. If the solution in excess of KCX be boiled with NaCIO, black Ni 2 (OH) 6 is pre- cipitated. Cf. 127. 134. Compounds of Ni color the borax bead red- dish brown in the oxidizing flame ; grey in the reducing flame. Characteristic Reactions ; 130, 131. ANALYSIS. (a) Add to the solution or filtrate from Group III (N~H 4 ) 2 S till the precipitation is complete. Warm until the precipitate subsides ; filter and wash with hot H 2 to which a little (NH),S has been added. The filtrate may contain Groups V and VI. The precipitate consists of one or more of the sulphides of Group IV. If light colored, Co and Ni must be absent ; if dark, one or both of these metals is pres- ent. I. All the group may be present. Treat the precipitate with cold HOI. Filter and wash. (b) The residue consists of CoS, NiS, or both. Test for Co with the borax bead (128). (1) If Co is ANALYSIS. 21 -absent, the bead shows the presence of Ni. Dissolve the residue in a small amount of aqua regia, expel excess of acid, dilute and confirm the presence of Ni by special reactions. (2) If Co is present, dissolve the residue in aqua regia, expel excess of acid, add .a cone, solution of KN0 2 and acetic acid. After standing for several hours in a warm place the Co is all precipitated. Filter and test the filtrate for Ni by adding NaOH. (c) The filtrate may contain ZnCl 2 , MnCl 2 , or both. Boil to expel H 2 S, and add excess of NaOH. Of. 116 and 120. A precipitate is Mn(OH) 2 ; filter .and confirm the presence of Mn by 117. Test the .filtrate for Zn by 119. II. Co and Ni absent. Dissolve in HC1 and exam- ine the solution as in I. c. EXERCISES. XIX. Draw up a table for the analysis of this .group. XX. In what other ways can Ni be detected in the presence of Co ? XXI. NH 4 OH is added to an acid solution con- taining the members of the first four groups ; what does the precipitate contain ? What change will the addition of an excess of NH 4 OH produce ? How can the precipitate be examined ? XXII. To a solution containing all of the third :and fourth groups, (NH 4 ) 2 S is added ; of what does the precipitate consist ? How can it be analyzed ? 3 22 QUALITATIVE ANALYSIS. XXIII. A solution is known to contain Zn or Al, or both ; how is it to be examined ? XXIV. Describe the important compounds of the members of this group and their uses. Group Y. KEACTIOJSTS. Barium. Ba". Solution, BaCl 2 . ^ 135. (NH 4 ) 2 C0 3 or Na 2 C0 3 precipitates white BaCOg ; soluble in acids, even in acetic acid. 136. Na 2 HP0 4 precipitates white Ba 2 HP0 4 . / 137. H 2 S0 4 , or a soluble sulphate, precipitates, even in dilute solutions, white BaS0 4 ; insoluble in acids. 138. CaS0 4 or" 1 SrS0 4 precipitates immediately BaS0 4 . 139. K 2 Cr0 4 precipitates yellow BaCr0 4 ; soluble in HC1 ; reprecipitated by NH 4 OH ; insoluble in acetic acid. 140. H 2 SiF 6 precipitates white BaSiF fi . 141. (NH 4 ) 2 Ox precipitates white BaC 2 4 from moderately strong solutions ; soluble in acetic acid. 142. Barium compounds give a yellowish green flame coloration. Characteristic Keactions ; 137, 142. Strontium. Sr". Solution, SrCl 2 . 143. Of. 135 and 136. 144. H 2 S0 4 precipitates white SrS0 4 ; slightly sol- uble in H 2 0, and hence does not appear at once in less insoluble in acids than BaS0, GROUP V ; REACTIONS; 23 145. CaS0 4 precipitates slowly on standing SrS0 4 . 146. K 2 CrO 4 precipitates, only in cone, solutions, yellow SrCr0 4 . Presence of acetic acid prevents the precipitation. 147. H 2 SiF 6 produces no precipitate. 148. (NH 4 ) 2 Ox precipitates white SrC 2 4 ; soluble in HC1 ; only slightly soluble in acetic acid. 149. Strontium compounds produce a crimson flame coloration. Characterictic Reactions ; 145, 149. Calcium. Ca n . Solution, CaCl 2 . 150. Of. 135 and 136. 151. H 2 S0 4 precipitates, from strong solutions, CaS0 4 ; less insoluble in H 2 and acids than SrS0 4 . 152. CaS0 4 , K 2 Cr0 4 , and H 2 SiF 6 give no precipi- tates. 153. (NH 4 ) 2 Ox precipitates white CaC 2 4 ; soluble in HOI, but insoluble in acetic or oxalic acid. 154. Calcium compounds give a dull red flame col- oration. Characteristic Reactions ; 153, 154. ANALYSIS. The solution or filtrate from Group IV if tur- bid or colored, is boiled till clear and filtered from deposited impurities. If acid, the solution must be rendered alkaline with NH 4 OH. Add NH 4 C1 and then precipitate by adding (NH 4 ) 2 C0 3 to the warm solution. Filter and wash with hot H 2 0. The filtrate may contain Group VI. The precipitate consists of one or more of. the car- 24 QUALITATIVE ANALYSIS. bonates of Group V : BaC0 8 , SrCO,, CuCO,. Dis- solve in acetic acid. Preliminary test. To a small portion of the solu- tion in HAc, add CaS0 4 solution. An immediate- precipitate indicates that Ba is, and Sr and Ca may be present (I). A precipitate after some time shows that Ba is absent, but Sr is and Ca may be present (II). No precipitate indicates that Ba and Sr are absent and that Ca alone is present (III). I. All the Group may be present. Add to the HAc solution, K 2 Cr0 4 in slight excess and filter. The precipitate is BaCr0 4 ; dissolve in HC1 and test by 137 and 142. The filtrate is made alkaline with NH 4 OH and (NH 4 ) 2 C0 3 added. A precipitate is SrC0 8 , CaC0 3 , or both ; wash till white and dissolve in HAc. Test a small portion of this solution for Sr by adding CaS0 4 solution, or by the flame reaction (149). (a). If Sr is present, add a dilute solution of (NH 4 ) 2 S0 4 . After standing for some time, filter from the precipi- tated SrS0 4 and test the filtrate for Ca by adding NH 4 OH and (NH 4 ) 2 Ox (153). (b) If Sr is absent,, test at once for Ca by 153. II. Ba absent, Sr present. Proceed as in I, a. III. Ba and Sr absent. Test for Ca by 153. Group VI. REACTIONS. Magnesium. Mg". Solution, MgS0 4 . 155. NH 4 OH and (NH 4 ) a C0 8 give no precipitates in the presence of salts of ammonium. GROUP !VI ; REACTIONS. 25 156. Na 8 HP0 4 produces, in the presence of NH 4 OH and NH 4 C1, a white crystalline precipitate of MgNH 4 P0 4 . The precipitation is slow in dilute so- lutions ; but is hastened by warming and agitation. 157. H 2 S0 4 , H 2 SiF 6 and (NHJ.Ox produce no precipitates. 158. Ignited on charcoal, compounds of Mg yield an infusible luminous mass, which, on being mois- tened with Co2N0 3 and again ignited, assumes a pale rose color. Characteristic ; 156, 158. Potassium. K 1 . Solution for reactions, KC1. 159. PtCl 4 precipitates, except in very dilute solu- tions, yellow crystalline PtCl 4 ,2KCl ; insoluble in alcohol. 160. NaHTr or H 2 Tr precipitates white crystalline KHTr from concentrated solutions. 161. H 2 SiF fi precipitates white gelatinous K 2 SiF 6 . 162. Potassium compounds color the flame violet, appearing reddish-violet through blue glass. Characteristic ; 162. Ammonium. NH 4 '. Solution, NH 4 C1. L63. PtCl 4 precipitates yellow crystalline PtCl 4 , 2NH 4 C1 ; insoluble in alcohol. On ignition, the precipitate leaves a residue of spongy platinum. 164. NaHTr or H 2 Tr precipitates white crystalline NH 4 HTr from concentrated solutions. 165. H 2 SiF 6 gives no precipitate. 166. Nessler's solution produces a brown precipi- S* 26 QUALITATIVE ANALYSIS. tate, or in very dilute solutions a brownish-yellow coloration. 167. Heated with NaOH, compounds of NH 4 evolve NH 3 , which is recognized by its odor, alkaline reaction and fuming with HC1. 108. Heated on platinum, compounds of NH 4 volatilize completely. Sodium. Na 1 . Solution for reactions, NaOl. 169. Pt01 4 , NaHTr and H 2 Tr, give no precipitates. 170. H 2 SiF 6 precipitates white gelatinous Na 2 SiF B . 171. Sodium compounds produce an intense yel- low flame coloration, which is not visible through blue glass. A crystal of K 2 Cr 2 7 appears colorless when illuminated by the sodium flame. . ANALYSIS. The solution or filtrate from Group V is concen- trated by evaporation and a portion ignited on plati- num foil. If no residue is lef t, Mg, K and Na arc- absent. Test the original solution or substance for NH 4 by 167. If a residue is left, Mg, K, Na may be present. Test a small portion of the concentrated solution for Mg by 156, and then proceed with the examination for K and Na by I or by II according to the result. I. Mg is present. (a) Employ the flame tests, 162 and 171. A strong sodium flame masks a potas- sium flame ; but blue glass cuts off the yellow and al- lows the detection of K in the presence of Na. Or (b), evaporate the solution to dryness, ignite the residue to expel salts of NH 4 , dissolve it in a lit- GROUP VI ; ANALYSIS. 27 tie H 2 7 and add Ba(OH) 2 to alkaline reaction ; boil, filter ; The precipitate is Mg(OH) 2 . The filtrate contains Na and K, if present, as hydroxides, and the excess of Ba(OH) 8 ; precipitate the Ba with (NH 4 ) 2 C0 3 , filter and evaporate the filtrate to dry- ness and ignite. The residue can now contain only Nn. K. Test for K by 159, or 160 ; for Na by 171. II. Mg is absent. Evaporate the concentrated so- lution and ignite ; dissolve the residue in a little H 2 and test for K and Na as in I. b. A special test for NH 4 is always made by heating a portion of the original substance or solution with NaOH (cf. 167). EXERCISES. XXV. Draw up'tables for the analysis of Groups A" tind VI. XXVI. Give as many ways as possible for detect- ing K in the presence of Na. XXVII. Devise other ways for analyzing this group. XXVIII. Describe the important compounds of the members of Groups V and VI and give their uses. SECTION III. SYSTEMATIC ANALYSIS OF SOLIDS AND LIQUIDS. Chapter I. PRELIMINARY EXAMINATION. A. The Substance is a Solid. I. A portion of the powdered substance is heated in a glass tube sealed at one end. a. Water condenses on the cool part of the tube. This may indicate (1) adherent or enclosed (decrepita- tion) 1I 2 0. (2) Salts containing H 2 of crystalliza- tion (fusion followed by solidification). (3) Decom- posable hydrates. The water may be alkaline or acid, and thus indicate the presence of NH 4 or a volatile acid. b. Gasex or fumes are given off. 1. N0 3 recognized by its color and odor, indicates nitrates or nitrites. 2. Cl a , Br a or I 2 color and odor ; certain chlorides, bromides or iodides. 3. NH 3 odor, fumes with HC1 ; salts of NH 4 . 4. S0 2 odor ; sulphate or sulphite. 5. H 2 S odor ; hydrated sulphides. 6. CN" odor, crimson flame ; certain cyanides. 7. C0 2 extinguishes a match, renders a drop of lime water turbid ; carbonates and oxalates. PRELIMINARY EXAMINATION. 29 1 8. CO burns with bine flame ; oxalates. 9. 2 rekindles spark ; chlorates, nitrates or per- oxides. 10. N 2 rekindles spark ; NH 4 NO g or other nitrate with a salt of NH 4 . C. A sublimate is formed. If white, it may be : I. Salts of NH 4 ; heated with NaOH yield*NH 3 . 3. Chlorides of Mercury ; (a) Hg Cl sublimes without fusion ; is yellow while hot and white when cool, (b) HgCl 2 fuses before it sublimes. 3. As 2 3 ; crystalline, gives As mirror when heated with charcoal in a glass tube. 4. Sb 2 3 melts and sublimes in needles. .">. Certain organic acids. If yellow, it may be : 6. S ; sublimes in reddish brown drops, which turn? yellow on cooling ; sulphur or certain sulphides. 7. As 2 S 3 ; reddish while hot, yellow when cool. 8. HgI 2 ; turns red when rubbed. If dark or of metallic lustre, it may be : 9. I Q ; feathery and black. Cf. b. 2. 10. HgS ; black, becomes red when rubbed. II. Hg ; grey mirror, white globules when rubbed. d. The substance or residue changes color. 1. If the substance blackens it may be from the formation of a black oxide, or from the charring of organic matter. In the latter case smoky fumes and tar are usually evolved ; acetates give the odor of acetone ; tartrates the odor of burnt sugar ; organic salts of the alkalies and alkaline earths yield carbonates which effervesce with acids. 30 QUALITATIVE ANALYSIS. 2. The residue shows one of the following changes : Yellow while hot, white when cold ; ZnO. Yellow brown " " yellow " " SnO... Red brown " " pale yellow " " Bi 2 3 . Red brown " " yellow " <; PbO. Black " " red " " Fe,0 3 . e. The substance fuses wit '/tout decomposition or sublimation. Salts of the alkalies and certain salts of the alkaline earths (nitrates, chlorides, etc). II. A small portion is heated on charcoal before the blowpipe. 1. The substance deflagrates; ait rates or chlorates. 2. It melts and runs into the charcoal ; salts of the alkalies and sonic salts of the alkaline earths. 3. It gives off S0 2 ; sulphur or sulphides. 4. It volatilizes ; cf. I. c. 5. It gives a coating on the charcoal ; cf. III. b. 6. An infusible white residue remains. Moisten with Co2NOU;nid ignite ; a blue color indicates Al, Si0 2 , or })^fs8f8iates ; green, Zn : pink or rose, Mg. III. A small portion of the finely jtowdered sub- stance ismfapd with Na z C0 3 and heated on charcoal in the inher^lqwpipe flame (reduction). a. Metallic globules or particles are obtained with- out a coating on the charcoal. Ag, Cu, Au yield globules ; Pt, Fe, Co, Ni yield no globules, but in- fusible metallic particles, all of which except Pt are jnagnetic. b. A coating on the charcoal is produced, with or PRELIMINARY EXAMINATION. 31 without the formation of a metallic bead. The coating is : 1. White, very volatile, emitting a garlic odor ; na globule ; As. 2. White, less volatile than (1) ; globules usually formed, which are brittle and hard ; Sb. 3. Yellow while hot, turns white on cooling, close to the substance, no globules ; Zn. 4. Pale yellow while hot, white on cooling, non- volatile ; globules formed with difficulty, which are malleable and readily fusible ; Sn. 5. Lemon yellow, volatile; globules readily formed, easily fusible, soft and malleable ; Pb. 6. Orange yellow while hot, becomes lemon yellow on cooling, volatile ; globules hard and brittle ; Bi. 7. Reddish-brown and volatile ; no globule ; Cd. C. The fused mass is removed from the charcoal and crushed on a silver coin with a drop of water. The silver is stained brown or black (Ag 2 S) ; sul- phides or sulphates in the original substance. IV. A small portion is fused in a borax bead formed in a loop of platinum wire. BORAX BEADS. Outer Flame. Metal. Inner Flame. HOT. COLD. Green. Green. Or. Green. Green. Blue. Cu. Opaque and reddish. Blue. Blue. Co. Blue. Violet. Brown. Ni. Grey and cloudy. Violet. Amethyst. Mn. Almost colorless. Red. Yellow. Fe. Bottle green. 32 QUALITATIVE ANALYSIS. V. A clean platinum wire is moistened with HCl, dipped into the powdered substance and held in the -edge of the Bunsen flame. The flame is colored 1. Yellow, not visible through blue glass ; Na. 2. Violet, reddish violet through blue glass ; K. 3. Crimson, Sr. 4. Orange red ; Ca. 5. Green ; 1I 3 BO S . 6. Yellowish green ; Ha. 7. Blue changing to green ; Cu. VI. // the substance is not a metal, a small portion /x /nixed with cone. H n SOi in a dry test tube and the mixture carefully heated, if a reaction does not take place in the rol<(. a. The following gases may be evolved : IIC1, HBr+Br 2 , I Q , HF, HCN, HNO, HAc, from their respective salts ; (1IF is partially converted into SiF 4 , which renders turbid a drop of I.I a O'Oii the end of a glass rod) ; CO Q from carbonates ; S0 g from sulphites or thiosulphates or by tartrates ; N0 2 from nitrites ; II..S from sulphides ; 2 from perox- ides, chromates (turn green), permanganates (become colorless) ; CO from oxalates or ferrocyauides ; Cl from hypochlontes ; C1 2 4 from Chlorates. b. Blackening of the mixture indicates organic matter. VII. After finishing the preliminary examination, treat the substance 'with solvents. See chap. II. p. 34. PRELIMINARY EXAMINATION. 33 B. The Substance is a Liquid. I. A few drops are carefully evaporated on platinum foil to dryness. a. No residue remains ; H 2 and some other vol- atile liquids. b. A residue remains ; 1. Which disappears on ignition ; compounds of NH 4 , Hg, As, Sb or certain organic acids. Cf. A. I. c. 2. Which changes color. Cf. A. I. d. 3. Which fuses without volatilizing. Cf. A. I. e. 4. Which may be further examined by A. II-VI. II. Test with Litmus paper (blue and red). a. The solution is neutral ; only a few salts can be present, chiefly chlorides, nitrates, and sulphates of the alkalies or alkaline earths. b. The solution is acid. It may contain : (1) a free acid or acid salt, (2) a normal salt with acid re- action. In the first case a drop of Na 2 C0 3 solution gives no permanent precipitate ; in the second, the turbidity or precipitate usually remains. C. The solution is alkaline. This indicates the presence of hydroxides, sulphides, or certain salts of the alkalies or alkaline earths. III. Proceed to the analysis by chap. III. 34 QUALITATIVE ANALYSIS. Chapter II. SOLUTION OF SOLIDS. A. The Substance is neither a Metal nor an Alloy. I. Add some water to a small quantity of the finely powdered substance in a test tube ; heat, and finally boil if necessary. a. Complete solution takes place. Dissolve a larger portion sufficient for analysis, and after examining the solution with test-papers (cf. chap. I. B. II.), proceed with the examination according to chap. III. b. If a considerable residue remains undissolved, it is usually best to consider the substance insoluble in water, and proceed according to II. Whether par- tial solution has taken place or not can be ascertained by filtration and evaporation on platinum foil (cf. chap. II. B. I). If the residue is quite small, it is well to filter and treat the solution according to chap. Ill ; the residue according to B. C. Soluble in water are : All nitrates, chlorates and hypochlorites ; nitrites (AgNO^ sparingly) ; acetates (AgAc and Hg^Ac^ sparingly) ; sulphates except those of Ba, Sr, Ca, Pb ; chlorides, bromides and iodides except those of Ag, Hg^ (Pb) ; the bo- rates, carbonates, oxalates, phosphates and sulphites of the alkalies ; the oxides, hydroxides, sulphides, cyanides, ferrocyanides and ferri cyanides of the al- kalies and alkaline earths ; the fluorides of the alka- lies and of Ag, Sn, Hg, Bi, Sb, Al, Or and Fe iv . SOLUTION OF SOLIDS. 35 II. Substances insoluble in water are treated with acids in the following order, till they dissolve or prove to be insoluble in all acids : HC1, HN0 3 , aqua regia. The acid used is first dilute, then con- centrated ; and in each case is heated before passing to the next. If solution takes place, proceed accord- ing to chap. Ill, if not, see III. It is important to avoid using an excess of acid, especially if HN0 3 or aqua regia is the solvent. III. Substances insoluble in wafer and acids. The most common are : sulphates of Ba, Sr, (Ca), Pb ; AgCl, AgBr, Agl, AgCN, CaF a ; ignited Al,0 3 , Fe 2 3 , Cr 2 3 ; Sn0 2 ; Si0 2 and many silicates ; cer- tain ferrocyanides and ferricyanides ; S and C. The preliminary examination gives a clue to the composition of most of these. C is black and infus- ible, but disappears when ignited on platinum foil (graphite and gas carbon are scarcely affected) ; deflagrates when heated with KN0 3 . Si0 2 and sili- cates swim undissolved in a bead of microcosmic salt. (1) Silicates are mixed with four times the quan- tity of K,C0 3 -bNa a C0 8 and fused in a platinum crucible. When cool add H 2 and a little HC1 and evaporate to dryness. On treating the residue with H 2 0, silica remains undissolved, while the metals, which were originally present as silicates, go into so- lution as chlorides. If an insoluble silicate is to be examined for Group VI, fuse with Ba(OH) 2 , or dis- solve in HF. (2) Sulphates of Ba, Sr, Ca, and A1 2 3 , Fe 2 3 are fused as in 1 ; the fused mass is washed with 36 QUALITATIVE ANALYSIS. H 2 as long as anything dissolves ; filter and dis- solve the residue in HC1. (3) PbS0 4 may be dissolved in ammonium tartrate ; AgCl, AgBr, Agl and AgCN may be dissolved in KCN or reduced by Zn+H 2 S0 4 . (4) CaF 2 is decomposed by cone. H 2 $0 4 in a plati- num or lead dish. (5) Sn0 2 is fused in a porcelain crucible with equal parts of Na 2 C0 3 and S. The fused mass is extracted with H 2 and SnS a prec. by HC1. (6) Insoluble compounds of Cr are fused in a plat- inum crucible with equal parts of Na 3 C0 8 and KN0 3 . Boiling H 2 dissolves from the mass K 2 (Jr0 4 . A residue insoluble in H 2 is dissolved in IIC1. (7) Ferrocyanides and ferricyanide* are decom- posed by boiling NaOH into ferrocyanides and ferri- cyanides of Na soluble in H 2 0, and hydrates of the metals soluble in acids. After a solution is obtained it is examined accord- ing to chap. III. B. The Substance is a Metal or an Alloy. It is treated with HN0 3 , and boiled if necessary : a. Complete solution takes place. Au, Pt, Sb and Sn are absent. b. A residue is left ; (a) if metallic : Au, Pt ; dis- solve in aqua regia. (b) Residue is white: Sb, Sn, or certain nitrates sparingly soluble in HN0 3 . Treat with H 2 ; the nitrates dissolve ; to a residue, add hot cone. H,Tr ; Sb dissolves and is tested with H 2 S ; Sn remains undissolved and may be treated by III, 5. ANALYSIS OF SOLUTIONS. 37 Chapter III. EXAMINATION OF SOLUTIONS FOR METALS. a. 'Add to the solution a few drops of HC1 or enough to render it distinctly acid, if originally alka- line. A precipitate shows the presence of Group I (cf. g) ; see p. 5, Analysis. b. To a small test of the solution in which HC1 has failed to produce a precipitate, or of the filtrate from Group I, add H 2 S until the odor is distinct af- ter shaking and warming gently. If no precipitate or turbidity is produced, pass to c. If H 2 S causes a precipitate or turbidity, add the test to the solution and treat the whole with H 2 S (cf. h) ; see p. 8, Pre- cipitation of Group II, and pp. 9 and 13, Analysis. c. To a fresh test of the original solution, or to a test of the filtrate from Group II from which H 2 S has been expelled by boiling and which contains no ferrous Fe (cf. p. 16, Analysis), add NH 4 C1 and NH 4 OH. If no precipitate is formed, pass to d. A precipitate shows the presence of Group III (cf. i) ; see p. 16, Analysis. d. To the test in which NH 4 OH procured no pre- cipitate, or to a test of the filtrate from Group III, add (NH 4 ) 2 S. If no precipitation takes place, pass to e. A precipitate shows the presence of Group IV ; see p. 20, Analysis. e. To the test which NH 4 OH and (NH 4 ) 2 S failed to precipitate, or to a test of the filtrate from Group IV, add (NH 4 ) 2 C0 3 . * A precipitate shows the pres- 4 38 QUALITATIVE ANALYSIS. ence of Group V ; see p. 23, Analysis. If no pre- cipitate is formed, examine the solution or filtrate for Group VI according top. 26, Analysis. Notes on the precipitation and separation of Groups. f. When a group is found to be present, the group reagent must be added till it is completely precipita- ted. This is the case, if, after thorough agitation, addition of another drop of the reagent produces no precipitate, or the solution smells of the reagent. At the same time a large excess of the reagent is to be avoided. The precipitates must be thoroughly washed to free them from adhering solution which may contain the succeeding groups. g. Group I. If the solution is alkaline, HC1 may precipitate As a S 3 , Sb a S 3 , SnS 2 (cf. p. 13, a) ; cyanides dissolved in KCN ; gelatinous (HO) 4 Si ; or S from alkaline sulphides. HC1 may also cause the evolu- tion of CO,, H 2 S, S0 2 sometimes attended by sep- aration of S, or HCN(cf. p. 32, VI, a). SbOCl and BiOCl are sometimes precipitated at first by dilute HC1, but dissolve when more acid is added. h. Group II. The solution into which H 2 S is led must not be strongly acid even with HC1, as in this case the sulphides of the group especially CdS are not readily precipitated. The difficulty may be cor- rected by dilution or evaporation. At the same time the solution must be sufficiently acid to prevent par- tial precipitation of ZuS. Turbidity on dilution in- dicates the presence of Bi or Sb (cf. 40 and 70). i. Group III. The precipitate almost always con- tains some Mn when this is present in the solution NOTES ON ANALYSIS, 39 under examination. Its presence is shown by the green color of the mass obtained in testing for Or. The green manganate is decomposed on boiling with H 2 and Or is detected in the usual way in the fil- trate, cf. p. 17, d. j. On account of the imperfect separation of Groups III and IV by means of NH 4 C1 and NH 4 OH, it is in some cases best to precipitate both groups by (NH 4 ) 2 $. HC1 dissolves all but CoS and NiS. The filtrate is freed from H 2 S ; ferrous Fe, if present, is oxidized by HC1 and KC10 3 , and the solution when cold is treated with BaC0 3 . After shaking several times during twenty minutes, filter and wash. The precipitate contains hydroxides of Fe, Or and Al, and excess of BaC0 3 ; the filtrate Zn, Mn and Ba01 3 . k. The precipitate produced by NH 4 OH may con- tain or consist of phosphates or oxalates of the alka- line earths, as these substances are only soluble in acid solution*. They need not be looked for if the original substance was soluble in H 2 0, or if the orig- inal solution was alkaline. Tests for phosphoric and oxalic acids should, however, be at once made (a) when a precipitate for Group III is obtained which further examination shows to contain none of the groups ; (b) or when a precipitate is obtained for Group III, and none for Group V or Mg, although the Preliminary Examination has indicated the presence of one or more of these metals. (1) If an oxalate is detected, a portion of the original substance is ignited. The oxalate is thus converted into a carbonate which is dissolved in HC1 and examined in the usual way. 40 QUALITATIVE ANALYSIS. (2) If a phosphate is present, add to the Group III precipitate a considerable quantity of metallic tin and cone. HN0 3 . Heat until all the tin is oxi- dized. Phosphate of tin, insoluble in HN0 3 is thus formed. Dilute with H 2 0, filter and examine the filtrate, which contains the nitrates of the metals originally present as phosphates, in the usual way. EXERCISES. XXIX. Name the most important metals and alloys and their uses. XXX. On adding the reagent for Group II to a solution, no precipitate is formed, but the solution becomes turbid ; to what may this be due ? XXXI. Chromates give no precipitate with NH 4 OH; how then is Cr detected in the ordinary course of analysis when present in the original solution as chromate ? XXXII. A solution containing Fe, Al, Co, Cu, Zn, Mn and free acetic acid is treated with II 8 8 ; what precipitation, if any, takes place ? XXXIII. A solution contains members of Groups II, III, IV and V : (a) The precipitation by H 2 S is incomplete ; how may this affect the examination of the following groups ? (b) The precipitate formed by H 2 S is complete but is insufficiently washed; what difficulties may arise in its examination ? XXXIV. Solutions of Bi and Sb are both precipi- tated by H 2 ; how can the precipitates be distin- guished ? EXERCISES. 41 XXXV. Why must H 2 S be expelled from the fil- trate of Group II before boiling with HN0 3 ? XXXVI. How may the examination of a solution be simplified if it is known that it contains but one metal ? XXXVII. How are the precipitate and filtrate obtained in the method of separating Groups III and IV by BaC0 3 (cf. p. 39, j), to be further examined ? XXXVIII. A solution contains Al, Ni, Mn, Zn and free HC1. After the addition of a certain re- agent, H 2 S precipitates ZnS alone from the solution. What is the reagent employed ? XXXIX. The filtrate from Group IV is often brown. What is the reason of this ? How can the color be removed ? XL. How can a ferrous salt be detected in the presence of a ferric compound ? XLI. How is bismuth chromate distinguished from lead chromate ? XLII. NaOH is added in excess to a solution con- taining members of the first four groups ; of what may the precipitate consist ? What change will be produced by boiling ? XLIII. H 2 S0 4 is added to the filtrate from Group I ; of what may the precipitate consist ? FART II. DETECTION OF THE ACIDS. SECTION I. REACTIONS OF THE ACIDS. Group I. ACIDS WHICH ARE PRECIPITATED FROM NEUTRAL SOLUTIONS BY BaCl 2 . Sub-group A : Acids whose Barium mils are insoluble in #6^: H 2 S0 4 , (HJSiF.). Sulphuric Acid and Sulphates. See Reac- tions 137, 16 and p. 31, c. 172. Free H 2 S0 4 may be detected by putting a few drops of the solution on writing paper and gently warming. The acid, if present, will be concentra- ted and blacken the paper. Hydrofluo-silicic Acid and Silico-fluorides. See Reactions 140, 161, 170. Solid silico-fluorides heated with cone, sulphuric acid give HF, which fumes and etches glass, and fluoride of silicon. REACTIONS OF ACIDS ; GROUP I, B. 43 Sub-group B: Acids wliose Barium Salfs are soluble in HOI : H 3 P0 4 , H 2 C0 3 , HF, (HO) 4 Si, (HO) 8 B, H 0x, H 2 Tr, H 2 Cr0 4 , H 3 As0 4 , H 3 AsO,,