Having now given the principal reactions for the most important metals, we will proceed to the examination of the alkali metals, the alkaline earths, and some of the acid elements. THE ALKALI METALS 17. ~Ammonium, NH_{4}.~--This hypothetical compound is commonly classed among the alkali metals from its close resemblance to the members of this group. To detect the presence of this hypothetical metal, mix the assay with about four parts of Na_{2}CO_{3}, place in an ignition tube, and apply heat. The odor of the evolved gas will be recognized, and if a piece of red litmus paper be moistened and held at the mouth of the tube, it will be turned blue by the escaping ammonia gas. We are not authorized to infer the pre-existence of ammonium, however, from the appearance of this reaction, for the presence of nitrogenous organic matter in the substance, which would be decomposed by this treatment, would give rise to such a reaction. 18. ~Potassium.~--Potassium is recognized by the color which its salts impart to the Bunsen flame. If a portion of a salt of potassium be held on a platinum wire in the flame, it imparts a blue-violet tint which rapidly disappears. 19. ~Sodium.~--Like potassium, this alkali metal is detected by the color which its salts give to the flame. If a sodium salt be held on the platinum wire in the flame, it imparts an intense yellow color. The extreme delicacy of this reaction has been mentioned elsewhere. The value of this test is really lessened by its great delicacy, for it is possible to detect minute quantities of sodium in almost all substances, although it may not be in chemical combination. As an example, draw the platinum wire between the fingers, and then place in flame, and note presence of sodium. 20. ~Lithium, Li_{2}O.~--In the Bunsen flame on the platinum wire it imparts a carmine-red tinge. Hydrochloric acid on the sample augments the coloration. THE ALKALINE EARTHS 21. ~Barium, BaO.~--In the Bunsen flame on the platinum wire it imparts an apple-green coloration. This reaction is intensified by moistening the sample with hydrochloric acid. 22. ~Calcium, CaO.~--In the Bunsen flame on the platinum wire it imparts an orange-red color, which appears gray when seen through blue glass. Hydrochloric acid on the sample makes the color more intense. 23. ~Strontium, SrO.~--In the Bunsen flame on the platinum wire it imparts an intensely red color, which is increased by converting the substance into the chloride. THE ACID ELEMENTS 24. ~Borates.~--If the substance be finely powdered, moistened with glycerine, and then placed on a platinum wire in the Bunsen flame, it imparts a brilliant green color. If turmeric paper be dipped into a solution of a borate, and then be dried at 100° C., it is turned to a peculiar red color. These two reactions are extremely delicate.