very malleable beads. Dissolve in aqua regia, absorb the yellow solution on filter paper, and moisten with SnCl, yields purple of Cassius. Platinum.-Reduced on charcoal splinter yields a grey spongy mass, which becomes lustrous when rubbed in the mortar. Observe insolubility in HCl and in HNO, and solubility in aqua regia, forming a light yellow solution. Iron.-Reduced on charcoal splinter, yields no bead, but minute metallic particles. Crush the end of the splinter in an agate mortar with a little water, and stir gently with a magnetized knife-blade. The finely divided metal will adhere to the knife. Rub this off on filter-paper, dissolve in aqua regia and add K4Fe(CN): observe the blue coloration from formation of Prussian blue. Borax bead: In the oxidizing flame when hot, yellow to brownish red. Nickel.—Reduced on charcoal splinter, yields white lustrous ductile particles, which form a brush on the point of the magnetized knife-blade. Rub these on paper and dissolve in HNO3, and observe the green colour produced. Borax bead: In the oxidizing flame, greyish brown or dirty violet. Upper reducing flame, grey from reduced nickel, which often collects to a spongy mass, leaving the bead colourless. Cobalt.-Reduced on charcoal splinter, yields white lustrous ductile particles, which adhere to the magnetized knife-blade. Rub these on paper and moisten with HNO3: observe the red colour, which changes to green on addition of HCl and drying; moisten with water, and observe the disappearance of the colour. Borax bead: In the oxidizing flame, bright blue, unaltered in the lower reducing flame. 60. The following metals are most easily recognized as compounds :-CHROMIUM, MANGANESE, URANIUM. Chromium.-Heated on platinum foil with Na2CO ̧ and with repeated additions of KNO„, yields a yellow mass soluble in water to a yellow solution. Manganese.-Borax bead amethyst-coloured in the oxidizing flame, colourless bead in the reducing flame. Heated with Na,CO, and KNO, yields a green bead, soluble in water to a green solution, which turns red on addition of acetic acid. Uranium.-Borax bead yellow, in the oxidizing flame, which becomes green in the reducing flame, especially on addition of SnCl2. The following tests for phosphorus and sulphur compounds are exceedingly delicate :— Phosphorus.-Ignite the sample, and then powder finely and place in a small test tube about the thickness of a straw, along with a piece of magnesium wire about five millimetres long, which should be covered by the powder. Now heat, and observe the incandescence caused by the formation of magnesium phosphide. Moisten the residue, and observe the highly characteristic smell of phosphuretted hydrogen. Sulphur. Reduced on charcoal splinter with Na2CO3, yields Na,S. Break off the charcoal point, place it on a silver coin, and moisten with a drop of water. The silver is at once blackened, owing to the formation of silver sulphide. 61.-PRELIMINARY EXAMINATION OF SINGLE SALTS. Before proceeding to the systematic analysis of single salts or mixtures, it is always advantageous to subject substances to a preliminary examination, in order to ascertain the probable nature of the substance The tables A and B, which follow, are adapted for the detection of single salts, either soluble or insoluble. TABLE A. PRELIMINARY EXAMINATION OF SINGLE SALTS CONTAINING ONE ACID AND ONE BASE. • EXAMINATION FOR ACID.* Heat the substance in a dry tube, and observe whether(a) Water is given off. Test its reaction with litmus paper. Acid reaction indicates Sulphites, Chlorides, &c. (d) The substance darkens in colour. This indicates the presence of Organic matter. Take a fresh portion of the substance, add HCl, and observe whether (e) A gas is evolved with effervescence. Try if the substance is soluble in water; if so, add Ba Cl2 solution to a portion of the solution, and observe if a precipitate form. White and insoluble in HCl indicates Sulphates. • Certain substances, not acids (e.g. mercury, sulphur, ammonia), are for convenience included here. White and soluble in HCl indicates Phosphates, Silicates, Oxalates, Borates, and Fluorides. Also Carbonates and Sulphites (see e). Yellow indicates Chromates (see e). If Ba Cl2 has given no precipitate, add Ag NO3 to another portion of the solution, and observe if a precipitate form. White indicates Chlorides. Also Cyanides (see e). Black indicates Sulphides (see e). (g) If neither water nor HCl has dissolved the substance, try nitric acid; and if this does not dissolve it, try aqua regia; and if that does not dissolve it, examine it according to the methods described in the following table (B). NOTE. If the substance is dissolved in H NO3 or aqua regia, it must be evaporated to dryness with HCl before proceeding to the examination for base (8). B. EXAMINATION FOR BASE. A solution having been obtained, observe (2) If H Cl produce a precipitate, it indicates Silver, Lead, or Mercurous Salts. (i) If H Cl + H2S produce a precipitate, it indicates Mercuric Salts, Lead, Bismuth, or Copper (black). Stannous Salts (brown). (j) If (NH4) HO + NH4 Cl + (NH4)2S produce a precipitate, it indi cates Iron, Nickel, or Cobalt (black). Zinc or Aluminium (white). Manganese (flesh-coloured). Chromium (green). (k) If (NH4) HO + NH4Cl + (NH4)2 CO3 produce a precipitate, it indicates (2) If not precipitated by the above reagents, it indicates— Magnesium, precipitated by Na, HPO4 (white). Sodium yellow). (Ammonium Salts (heated with NaHO gives smell of NH3). |