G. Strontium, and Calcium. (NH4)2CO3, and filter. Wash precipitate with hot H2O, dissolve in HCl, a precipitate after some time indicates Strontium, or a dilute Barium the solution in HCl add H2SO4, and boil to remove Ba and Sr. Filter. precipitate indicates Calcium. STRONTIUM. Ca PRESENT. III. Ba AND Ca PRESEnt. precipitate with H2SO4. Add H2SO4 to the HCl solution (diluted to prevent precipitation of Calcium), and filter. wash well. FILTRATE. da. Neutralize the solution with (NH4)HO, and RESIDUE. Ba SO4, Sr SO4. Boil in a beaker with a little water, test with C2(NH4)204 together with a mix- METHOD. and evaporate to dryalcohol. Filter. FILTRATE. Ca. Confirm as above. ture of three parts FILTRATE. Ca. Neutralize the solution with (NH4)HO, and test with C2(NH4)2O4 White precipitate indicates Calcium. ANOTHER METHOD. Dissolve the carbonates in C2H4O2, and precipitate the Ba with K2CrO4. Filter. Precipitate the Sr and Ca by (NH4)2CO3, and proceed as in Method II. (Ba Absent, Ca Present). Reactions of the Metals of the Potassium Group. 89. Metals whose solutions are unprecipitated by the preceding group reagents, but which have no common precipitant, and are therefore recognized by individual tests. Magnesium, Potassium, Ammonium, Sodium. MAGNESIUM. Mg, c.w. 24. 4. 1. Na,HPO, produces, in presence of (NH)HO and NHCl, a crystalline white precipitate of MgNHPO From dilute solutions the precipitation is slow, but may be hastened by stirring with a glass rod. The precipitate is soluble in dilute mineral acids and in C,2HO2 but is almost insoluble in dilute solution of (NH1)HO. 2. (NH4)HO in neutral solutions produces a partial precipitation of the hydrate Mg(HO)2, but gives no precipitate in presence of NH4Cl, in which the hydrate is readily soluble. 3. H2SO4, H2SiF6, and C2(NH4)2O4 yield no precipitates. 4. Heated on charcoal in the blow-pipe flame, then moistened with CoCl2 and re-heated, a pink mass is obtained. 90. POTASSIUM. K, c.w. 39'I. 1. PtCl produces a crystalline yellow precipitate of 2 KCl+PtCl, except in dilute solutions, which are not precipitated. The precipitation is promoted by stirring, or by addition of alcohol. 2 Tartaric acid precipitates white crystalline hydro gen potassium tartrate from strong and neutral solutions. The precipitation is promoted by stirring. 3. H2SiF produces a white gelatinous precipitate of K2SiF6. 4. Heated on platinum wire in the non-luminous flame, a violet coloration is produced, which when viewed through a piece of blue glass appears reddish violet. 91. AMMONIUM. NH4, c.w. 18. 1. PtCl produces a crystalline yellow precipitate of .2 NH4Cl + PtCl, except in dilute solutions, which are not precipitated. The precipitate is insoluble in alcohol and ether, and when ignited leaves a residue of spongy platinum. 2. Tartaric acid produces, in strong solutions, a white precipitate of hydrogen ammonium tartrate, similar in appearance to the corresponding potassium salt. 3. Nessler's solution, added to ammonia or its salts, produces a yellow coloration, or, if the ammonia compound be present in large quantity, a brown precipitate. 4. NaHo or KHO solution when warmed with ammonia salts decomposes them, and NH, is evolved, which is recognized by its pungent odour, by its turning red litmus paper blue, and by its forming white fumes with a strong solution of any volatile acid, e.g. HCl. 5. Heated on platinum foil, all compounds of ammonia volatilize completely. 92. SODIUM. Na, c.w. 23. The soda salts are almost without exception soluble in water, so that the flame test alone serves to distinguish the salts of this metal. 1. Heated on platinum foil or wire in the nonluminous lamp flame, an intense yellow colour is produced, which, however, is not seen when viewed through blue glass. It is thus possible to distinguish potassium salts when mixed with sodium salts. TABLE H. GROUP V. 93 Separation of Magnesium, Potassium, Sodium, and Ammonium. The filtrate from the Barium Group is concentrated by evaporation, and a portion evaporated on platinum foil. If no residue is left on ignition, Mg, K, and Na are absent. Detection of K and Na. (1.) Mg. being | (2.) Mg. being absent. present. The original Το a portion substance or so- of the concentralution is heated ted cold solution Evaporate an- Evaporate the with Na HO in a add (NH4) HO other portion of solution to drytest tube. Pre- and Na2HPO4 the solution to ness, ignite resisence of Am-White crystalline residue, dissolve water, and add dryness, ignite due, dissolve in moniumshown precipitate deby smell, by the notes Magne-tity of water, fil-til the solution in a small quan- baryta water un white fumes with sium. HCl, and by its action on red litmus paper. To detect Na. Evaporate alcoholic solution (which must have a yellow colour, showing that excess of Pt Cl4 has been added) nearly to dryness, add a grain or two of sugar, and ignite residue. Exhaust with water, filter, evaporate to dryness; and if a residue be left, test it by flame reaction for Na. Yellow coloration indicates Sodium. ter if required, has an alkaline PART IV. REACTIONS OF THE ACIDS. 94. Grouping of the Acids. The acids do not admit of being grouped with the same precision as the bases, but they can be approximately classified by means of certain group reagents. They are divided into two great classes, Inorganic and Organic Acids. These are readily distinguished by the action of heat. Salts of Inorganic Acids when heated to redness are not charred; salts of Organic Acids are at once charred, owing to decomposition and consequent separation of carbon.* 95. Grouping of the Inorganic Acids. *GROUP I. (SULPHURIC ACID GROUP). Group reagent, BaCl, in presence of HCl. Sulphuric Acid, Hydrofluo-silicic Acid. The acids of this group are precipitated by BaCl2, and the precipitate is not dissolved on addition of HCl. * With the exception of acetic and formic acids. (See 128 and 129.) H |