GENERAL REACTIONS FOR THE DETECTION OF THE METALLIC ELEMENTS IN SIMPLE
COMPOUNDS
For the sake of convenience, rather than for scientific reasons, the
following compounds have been arranged in alphabetic order. Also the
oxides of the elements have been taken, since they exhibit the reactions
to best advantage.
The student should work through carefully each one of the tests and
satisfy himself as to the characteristic reactions of the various
elements, for only in this way can he expect to recognize the substances
when presented to him as "unknowns." It is advisable to provide a
note-book and rule it as follows:--
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BEHAVIOR OF SUBSTANCE |
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Before Bp.| Before Bp. | In ignition | In flame| In flame | After first |
on Ch. | on Ch. with | tube with | on | with borax| ignition |
alone | Na_{2}CO_{3}| Na_{2}CO_{3}| platinum| bead | with |
| | and Ch. | wire | | Co(NO_{3})_{2}|
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_Remarks_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ |
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_Substance_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ |
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1. ~Aluminum, Al_{2}O_{3}.~--Before the Bp. on Ch. Infusible. No change.
Before the Bp. on Ch. with Na_{2}CO_{3}. Forms an infusible compound
with slight intumescence.
In ignition tube with Na_{2}CO_{3} and Ch. No change. Moisture driven
off.
In flame on platinum wire. No change. Becomes incandescent.
In flame with borax bead. In O. F. dissolves slowly, forming a
colorless glass which remains so on cooling.
With Co(NO_{3})_{2}. Mass becomes blue upon re-ignition.
2. ~Antimony, Sb_{2}O_{3}.~--Before the Bp. on Ch. In O. F. volatilizes
without change. In R. F. is reduced and volatilized. White coating of
antimonious oxide deposited on Ch. Blue tinge imparted to flame.
Before the Bp. on Ch. with Na_{2}CO_{3}. Readily reduced. White brittle
bead. Very volatile, giving characteristic white coating.
In ignition tube with Na_{2}CO_{3} and Ch. Volatilized.
In flame on platinum wire. Volatilized. Colors flame greenish blue.
With borax bead on platinum wire. In O. F. dissolves to a colorless
glass.
With Co(NO_{3})_{2}.____
3. ~Arsenic, As_{2}O_{3}.~--Before the Bp. on Ch. Very volatile. Strong
garlic odor to fumes.
Before the Bp. on Ch. with Na_{2}CO_{3}. Reduced with emission of
arsenical fumes.
In ignition tube with Na_{2}CO_{3} and Ch. Volatilizes, forming a
mirror-like deposit of metallic As in the cooler part of tube.
In flame on platinum wire____
With borax bead on platinum wire____
With Co(NO_{3})_{2}.____
4. ~Bismuth, Bi_{2}O_{3}.~--Before the Bp. on Ch. Yields a
coating--orange-yellow when hot, lemon-yellow when cold. The yellow
coating usually has a white outline.
Before the Bp. on Ch. with Na_{2}CO_{3}. Easily reduced to metallic
bismuth. Yellow bead brittle, but less so than antimony.
In ignition tube with Na_{2}CO_{3} and Ch.____
In flame on platinum wire____
With borax bead on platinum wire. In O. F. small quantity dissolves to a
clear yellow glass, which becomes colorless when cold.
With Co(NO_{3})_{2}____
5. ~Cadmium, CdO.~--Before the Bp. on Ch. Gives a coating on the coal.
Reddish-brown when cold. Very volatile.
Before the Bp. on Ch. with Na_{2}CO_{3}. Readily reduced. The metal
volatilizes easily, giving the characteristic coating.
In ignition tube with Na_{2}CO_{3} and Ch.____
In flame on platinum wire____
With borax bead. In O. F. dissolves to a clear yellowish bead, colorless
when cold.
With Co(NO_{3})_{2}____
6. ~Chromium, Cr_{2}O_{3}.~--Before the Bp. on Ch. No change.
Before the Bp. on Ch. with Na_{2}CO_{3}. Cannot be reduced. Soda sinks
in Ch. and a green colored mass remains.
In ignition tube with Na_{2}CO_{3} and Ch.____
In flame on platinum wire____
~With borax bead.~ Dissolves slowly but colors intensely. Yellow while
hot, green when cold.
With microcosmic salt bead. Colors red when hot, green when cold.
With Co(NO_{3})_{2}____
7. ~Cobalt, CoO.~--Before the Bp. on Ch. In O. F. unchanged. In R. F. is
reduced to the metal and is magnetic.
Before the Bp. on Ch. with Na_{2}CO_{3}. Reduced to a gray magnetic
mass.
In ignition tube with Na_{2}CO_{3} and Ch.____
In flame on platinum wire____
With borax bead on platinum wire. In O. F. colors very intensely blue,
both hot and cold.
With Co(NO_{3})_{2}____
8. ~Copper, CuO.~--Before the Bp. on Ch. Fuses to a black globule, which
can be reduced with some difficulty.
Before the Bp. on Ch. with Na_{2}CO_{3}. Readily reduced to metallic
bead, which is red in color, hard, malleable.
In ignition tube with Na_{2}CO_{3} and Ch.____
In flame on platinum wire. Colors flame emerald-green.
With borax bead on platinum wire. In O. F. green when hot, blue when
cold.
With Co(NO_{3})_{2}____
9. ~Iron, Fe_{2}O_{3}.~--Before the Bp. on Ch. In O. F. unchanged. In R.
F. becomes black and magnetic.
Before the Bp. on Ch. with Na_{2}CO_{3} Reduced to a metallic powder,
magnetic.
In ignition tube with Na_{2}CO_{3} and Ch.____
In flame on platinum wire____
With borax bead on platinum wire. In O. F. red while hot, yellow when
cold.
With Co(NO_{3})_{2}____
10. ~Lead, PbO.~--Before the Bp. on Ch. Easily reduced to the metal, bead
very malleable. Coating yellow, surrounded by white ring.
Before the Bp. on Ch. with Na_{2}CO_{3}. Instantly reduced. Coats the
Ch. upon further blowing.
In ignition tube with Na_{2}CO_{3} and Ch. Reduced to the metal.
In flame on platinum wire. Tinges flame blue.
With borax bead on platinum wire. In O. F. dissolves easily, forming a
limpid glass.
With Co(NO_{3})_{2}____
11. ~Manganese, Mn_{2}O_{3}.~--Before the Bp. on Ch. At high temperature
turns red.
Before the Bp. on Ch. with Na_{2}CO_{3}. Is not reduced.
Before the Bp. in O. F. on platinum foil with Na_{2}CO_{3}. Transparent
green mass when hot. Opaque, bluish-green when cold.
In ignition tube with Na_{2}CO_{3} and Ch. Not reduced.
In flame on platinum wire____
With borax bead on platinum wire. In O. F. violet-red while hot,
amethyst-red when cold.
With Co(NO_{3})_{2}____
12. ~Mercury, HgO.~--Before the Bp. on Ch. Instantly reduced. Very
volatile.
Before the Bp. on Ch. with Na_{2}CO_{3}. Reduced and volatilized.
In ignition tube with Na_{2}CO_{3} and Ch. Sublimes condensing in the
upper part of the tube as a metallic ring which is seen with the lens to
consist of minute globules of mercury.
In flame on platinum wire____
With borax bead on platinum wire____
With Co(NO_{3})_{2}____
13. ~Nickel, NiO.~--Before the Bp. on Ch. In O. F. unchanged. In R. F.
reduced to metal, slightly magnetic.
Before the Bp. on Ch. with Na_{2}CO_{3}. Easily reduced to the metal.
In ignition tube with Na_{2}CO_{3} and Ch.____
In flame on platinum wire____
With borax bead on platinum wire. In O. F. violet while hot,
reddish-brown when cold.
With Co(NO_{3})_{2}____
14. ~Silver, AgO.~--Before the Bp. on Ch. Easily reduced to the metal.
White, malleable, hard bead. Coats the coal dark red near assay.
Before the Bp. on Ch. with Na_{2}CO_{3}. Instantly reduced to metallic
globule.
In ignition tube with Na_{2}CO_{3} and Ch. Reduced to the metal.
In flame on platinum wire____
With borax bead on platinum wire. In O. F. partially dissolved. Bead
becomes milk-white.
With Co(NO_{3})_{2}____
15. ~Tin, SnO_{2}.~--Before the Bp. on Ch. Coats the coal yellow while
hot, dirty white when cool. Not reduced.
Before the Bp. on Ch. with Na_{2}CO_{3}. Reduced to metallic tin. White,
hard, malleable bead. Coating white and close to assay.
In ignition tube with Na_{2}CO_{3} and Ch.____
In flame on platinum wire____
With borax bead on platinum wire. In O. F. small quantity dissolves to
limpid glass.
With Co(NO_{3})_{2}. Greenish-blue color.
16. ~Zinc, ZnO.~--Before the Bp. on Ch. Upon ignition becomes yellow. Is
not reduced.
Before the Bp. on Ch. with Na_{2}CO_{3}. Reduced to metal. Rapidly
volatilized, coating the coal white.
In ignition tube with Na_{2}CO_{3} and Ch.____
In flame on platinum wire____
With borax bead on platinum wire. In O. F. yellow while hot, limpid
glass when cold.
With Co(NO_{3})_{2}. Green mass.
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 deg. 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 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.
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 assay with four parts, Na_{2}CO_{3}, and fuse in an
ignition tube. When thoroughly fused the tube is broken, and the fused
mass 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 mass was placed.
Before going on to the next chapter, the student should assure himself
of his familiarity with the reactions just given, and he should practise
with various substances, the nature of which is unknown to him.