The Alkali Metals
17. Ammonium, NH4.—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 Na2CO3, 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, Li2O.—In the Bunsen flame on the platinum wire it imparts a carmine-red tinge.
Hydrochloric acid on the sample augments the coloration.