25. ~Bromides.~--Bromides treated with microcosmic salt and oxide of copper on platinum wire impart to the flame a greenish-blue color, the edges being decidedly green. 26. ~Chlorides.~--Chlorides are treated in the same way as bromides. The color imparted to the flame is azure-blue. To discriminate between bromides and chlorides more clearly, the substance is mixed with anhydrous potassium bisulphate and fused in an ignition tube. Bromine and sulphur dioxide are evolved (if the substance be a bromide), the tube being filled with a yellow gas possessing the characteristic odor of bromine. 27. ~Fluorides.~--A small portion of the substance in a finely powdered condition is placed in one of the ignition tubes, a strip of moist Brazil-wood paper is introduced into the open end, and heat is applied. Hydrofluoric acid is evolved, and the red color of the paper is changed into a straw-yellow. Mica, containing only 0.75% of fluorine, shows the reaction clearly. 28. ~Iodides.~--Iodides are treated, as the bromides and chlorides, in a bead of microcosmic salt with oxide of copper. The flame is colored green. Fused with potassium bisulphate in an ignition tube the violet vapors of iodine are evolved, and thus iodides may be distinguished from chlorides and bromides. 29. ~Nitrates.~--If a nitrate be heated upon charcoal before the Bp., violent deflagration occurs. If the substance containing the nitric acid be mixed with a _very small_ quantity of finely powdered potassium cyanide, the deflagration is accompanied with ignition and detonation. If the substance be mixed in a dry condition with dry potassium bisulphate, and is then heated in an ignition tube, red-brown nitrous fumes are evolved. This reaction takes place if there is but a small quantity of nitrate present. 30. ~Phosphates.~--Phosphates impart to the flame a bluish green color. The color is made more intense by moistening the substance with sulphuric acid, and then taking the paste so formed on the platinum wire and placing it in the Bunsen flame. 31. ~Silicates.~--Silicates, when treated with microcosmic salt on a platinum wire, suffer decomposition; the bases unite with the phosphoric acid to form a transparent glass in which the silica may be seen floating as a cloudy mass. The bead must only be examined for silica while hot, since on cooling it becomes opaque. 32. ~Sulphides.~--Many sulphides, when heated in an ignition tube, volatilize and give a sublimate of sulphur in combination with the metallic portion of the substance.