TABLE B. EXAMINATION OF INSOLUBLE SUBSTANCES. The following substances are, under certain circumstances, insoluble in acids, and must be examined specially :-Silica, Silicates, Aluminia, Aluminates, Oxides of Antimony, Chromium, and Tin, Chrome Iron Ore, Sulphates of Barium, Strontium, and Lead, certain Fluorides (e.g. of Calcium), certain Sulphides (e.g. of Lead), the Chloride, Bromide, and Iodide of Silver, Carbon, and Sulphur. Heat the substance in a dry tube, and observe whether (a) It fuses and volatilizes completely. Sulphur (smells of SO2). (b) It fuses, but does not volatilize. Iodide of Silver. Chloride, Bromide, or (Yields metallic silver on fusing on (c) It is infusible, but disappears on heating. Carbon (Deflagrates when heated with K NO3). (d) It is infusible, but darkened in colour while hot, regaining its colour on cooling. Tin Dioxide and Antimony Pentoxide. (Confirm by blow-pipe test-tin bead is malleable; antimony bead brittle.) Observe whether (e) It yields a green bead with borax or microcosmic salt. Chromium Oxide or Chrome Iron Ore. (f) It swims undissolved in a bead of microcosmic salt. Silica and Silicates. (Fuse with four times its weight of a mixture of K2CO3 and Na2CO3. Allow to cool, dissolve in water, add HCl, and evaporate to dryness. Silica will separate out as a gelatinous mass.) g) It yields a colourless bead, with microcosmic salt. Alumina. (Heated on charcoal and moistened with Co (NO3)2 and re heated, it yields a blue infusible mass.) It is white and infusible, but quite unaltered by heating. Lead Sulphate yields, when heated with Na, CO3 in blow-pipe reducing flame, malleable metallic bead. (See also i.) Barium Sulphate, fused with Na2CO3 yields BaCO3. Boil the fused mass with water, filter and wash; the residue dissolved in HCl yields BaCl2 (flame coloration, green), precipitated by SrSO4 solution. Strontium Sulphate, fused with Na2CO3 yields SrCO3. Boil the fused mass with water, filter and wash; the residue dissolved in HCl yields SrCl2 (flame coloration, crimson), precipitated by CaSO4 solution. Calcium Fluoride, heated with H2SO4, yields HF, which etches glass. (2) It is black and infusible, and yields a malleable nietallic bead when fused with Na2CO3 in the blow-pipe flame. Lead Sulphide. (Bead leaves black mark on paper; and, when dissolved in HNO3, gives a white precipitate on addition of H2SO4 The action of strong sulphuric acid often affords a valuable indication of the nature of salts, both soluble and insoluble. In addition to observing the action of hydrochloric acid (e, Table A), it is always advisable to try the action of strong sulphuric acid. Thus, evolution of indicates Sulphites (105). Chlorine Chlorine Tetroxide Hydrobromic Acid (+ Br. vapour) Hydriodic Acid (+ I vap ur) Nitric Acid Oxides of Nitrogen Thiosulphates (106). Cyanides (114) Peroxides, Acetic Acid Acetates 128). PART III. REACTIONS OF THE COMMONLY OCCUR. RING METALS, WITH THE METHODS OF THEIR SEPARATION. GROUPING OF THE METALS. 62. The metals are divided into five groups according to their behaviour with certain substances which are termed group reagents. These five groups are the following: GROUP I. (SILVER GROUP.)* Group reagent, HCl. Silver, Mercury, Lead. The chlorides of the metals of this group are insoluble in water, and are therefore precipitated on addition of HCl. • A characteristic metal in each group may conveniently be used to designate that group. Thus, we may say. Silver Group" and "Copper Group," in place of Groups I. and II. GROUP II. (COPPER GROUP.) Group reagent, H2S in presence of HCl. Mercury, Lead, Bismuth, Copper, Cadmium, Arsenic, Antimony, and Tin. The sulphides of the metals of this group are insoluble in HCl, and are therefore precipitated by H2S in an aqueous solution containing HCl. The three last metals, arsenic, antimony, and tin, form a subgroup, as their sulphides are soluble in (NH4)2、 whilst the sulphides of the remaining metals are insoluble in that reagent. GROUP III. (IRON GROUP.) Group reagent, (NH4)2S, in presence of NH4Cl and (NH4)HO. Iron, Nickel, Cobalt, Zinc, Aluminium, Manganese, and Chromium. The sulphides and hydrated oxides of the metals of this group are insoluble in water, and are therefore precipitated on addition of the group reagent. Aluminium and chromium are precipitated as hydrated oxides, the others as sulphides. GROUP IV. (BARIUM GROUP). Group reagent, (NH4)2CO3, in presence of (NH)HO and NH4Cl. Barium, Strontium, Calcium. The carbonates of the metals of this group are insoluble in water, and are precipitated on the addition of (NH4)2CO3; as, however, they are soluble in acids, (NH4)HO must be added when the solution is acid. GROUP V. (POTASSIUM GROUP.) Metals unprecipitated by the above group reagents. Magnesium, Potassium, Sodium, Ammonium. These metals have no common precipitant, and are therefore distinguished by individual tests. The student should at first have several metallic salts given to him, and be asked merely to determine to which of the above groups each salt belongs; he ought next to make himself familiar with the individual tests for each metal which follow, and then proceed to the separations of the different metals. It will also be well for him to attempt to frame a table of separations for each group before consulting those given in the book. |