The Elements of Blowpipe Analysis Part 5

In flame on platinum wire____

With borax bead on platinum wire. In O. F. yellow while hot, limpid gla.s.s when cold.

With Co(NO_{3})_{2}. Green ma.s.s.

Having now given the princ.i.p.al 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 cla.s.sed among the alkali metals from its close resemblance to the members of this group.

To detect the presence of this hypothetical metal, mix the a.s.say 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. ~Pota.s.sium.~--Pota.s.sium is recognized by the color which its salts impart to the Bunsen flame. If a portion of a salt of pota.s.sium be held on a platinum wire in the flame, it imparts a blue-violet tint which rapidly disappears.

19. ~Sodium.~--Like pota.s.sium, 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 quant.i.ties 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 gla.s.s.

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.

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 pota.s.sium 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 pota.s.sium 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_ quant.i.ty of finely powdered pota.s.sium cyanide, the deflagration is accompanied with ignition and detonation.

If the substance be mixed in a dry condition with dry pota.s.sium 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 quant.i.ty 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 gla.s.s in which the silica may be seen floating as a cloudy ma.s.s.

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.

A very delicate test for sulphur in whatever combination it may be found in a substance, and which may be performed with great ease, is to mix the finely powdered a.s.say with four parts, Na_{2}CO_{3}, and fuse in an ignition tube. When thoroughly fused the tube is broken, and the fused ma.s.s is placed on a bright silver coin, and a drop of water is added.

If the substance contains sulphur, a black spot will be observed on the coin where the fused ma.s.s was placed.

Before going on to the next chapter, the student should a.s.sure himself of his familiarity with the reactions just given, and he should practise with various substances, the nature of which is unknown to him.

CHAPTER IV