James Freeman Sellers.

An elementary treatise on qualitative chemical analysis online

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the oxygen of the air and prevents oxidation. Thus
the closed tube is used for reduction. The tube is
usually made of small, hard glass tubing, about .5 cm.
in diameter and 10 cm. long. First cut the tube to the
proper length, and then heat one end of it in the blow-
pipe flame till it is closed and well rounded off. While
red hot take it out of the flame and, holding it vertically
downward, blow steadily till a small bulb is formed.

For use, the bulb is about half filled with the sub-
stance, or with the substance mixed with a flux or
reducing agent ; and it is heated first with the smoky
flame to expel the moisture at a low temperature.
Often this heating is sufficient, but if a very high tem-
perature is required, the non-luminous flame must be
applied and the tube heated to the desired degree.



METHODS OF ANALYTICAL SEPARATION 45



TABLE II BEHAVIOR OF SUBSTANCES HEATED IN A
BULB-TUBE 1



1. Substance fuses and solidifies again . . .

2. Substance does not fuse, but changes color :
(a) Chars and evolves carbon dioxide . .
(6) Yellow while hot, white on cooling . .

(c) White while hot, brown on cooling . .

(d) White while hot, yellow on cooling .

(e) Orange while hot, yellow on cooling .

3. Substance gives off water



4. Substance sublimes



5. Substance gives off a gas :

(a) Violet vapors

(6) Red fumes of nitrogen oxides

(c) Oxygen (tested with glowing match) .

(d) Carbon dioxide (tested with lime water)

(e) Sulphur dioxide (detected by odor) . .
(/) Cyanogen (odor of almonds) ....



Compounds of alka-
lies and of alkaline
earths.

Organic substances.

Zinc oxide.

Bismuth oxide.

Lead oxide.

Tin oxide.

Water of crystalliza-
tion or constitu-
tion.

Ammonium salts.
Arsenic "

Antimony "
Mercury "

Sulphur,



Iodine and iodides.
Nitrates of heavy

metals.
Chlorates and

nitrates.
Carbonates of

heavy metals.
Sulphur

compounds.
Cyanides.



Experiment 14

(a) Heat some zinc sulphate in a bulb-tube, using the lumi-
nous flame first and then increasing the heat to dull redness.
Examine carefully, for all changes; whether water is given
off, the color of the salt while hot and when cold, etc.



46 CHEMICAL ANALYSIS

(&) In a bulb-tube heat some lead nitrate. Test the gas from
the bulb with a glowing splinter and note the color, odor, etc., of
the gas. Also notice the behavior of the solid substance.

(c) Heat some sodium acetate in a bulb and notice the odor
of the evolved gas, and the change in the solid.

(c?) Heat some ammonium carbonate in a bulb. The salt
sublimes and collects on the cold part of the tube.

Platinum Wire; the Bead Tests. The platinum wire
is used in two sets of tests those for simple flame
coloration and those for bead coloration. Flame colora-
tion will be discussed under another head.

Certain easily fusible acid salts, such as acid potas-
sium sulphate and borax, have the power of displacing
volatile acids and of combining with metallic oxides to
form fusible sulphates, phosphates, and borates.

It happens that many metals impart distinctive colors
to their fused mixtures with these salts, and that they
may often be identified by this means. A platinum
wire, provided with a glass handle and looped at the
free end, serves as a support for a bead of fused borax
or other fused acid flux. The loop of the clean wire is
heated to redness, dipped into the powdered flux, and
heated in the non-luminous flame till the loop is filled
with a clear bead. A very small piece of the substance
to be analyzed is stuck to the soft bead, and is then
heated with the blowpipe, first with the oxidizing, then
with the reducing, flame. It is necessary to continue
the blast till the substance becomes thoroughly incorpo-
rated in the bead. During the operation the following
observations should be made : whether the substance
fuses, whether the bead becomes transparent or remains



METHODS OF ANALYTICAL SEPARATION 47



cloudy, the color of the bead, and its behavior in the
oxidizing and reducing flames.

Experiment 15

(a) Make borax beadHests in both the oxidizing and reducing
flames with thin pastes of cobalt nitrate, chromium nitrate, and
ferrous sulphate.

(6) Fuse a small bit of glass in a bead of microcosmic salt. The
floating silica constitutes the skeleton bead, a test for silicates.

TABLE III BEHAVIOR OF SUBSTANCES FUSED IN BORAX
OR MICROCOSMIC SALT



OXIDIZING FLAME


REDUCING FLAME




1 Blue . .


Blue


Cobalt salts


2. Green


Green


Chromium salts.


3. Yellow . .


Dark green


Iron salts


4. Amethyst ....
5. Dark yellow


Colorless . . .
Gray. . . .


Manganese salts.
Nickel salts


6. Green (hot), blue (cold)


Red or colorless .


Copper salts.



Charcoal. Charcoal, as a support for ignition, pos-
sesses the following properties : it is a reducing agent
and greatly facilitates reduction processes ; it is infusi-
ble and has a low conducting power, and hence forms
an ideal crucible ; and since it is porous, it absorbs the
excess of fluxes and leaves the infusible substances on
the surface. It is used in blowpipe analysis as a sup-
port and reducing agent combined. A small conical pit
is bored with a knife blade or iron forceps handle near
one end of a piece of even grain, and the substance, or



48



CHEMICAL ANALYSIS



mixture of the substance and a flux, is placed in the pit
and heated in the reducing flame with a blowpipe.

Experiment 16

(a) Heat a small crystal of potassium nitrate on charcoal with
the blowpipe. It will flash up and consume some of the char-
coal. This kind of explosive combustion is called deflagration.

(b) Heat some lead oxide (litharge) with three times its weight
of fusion mixture and a little potassium cyanide on charcoal with
the blowpipe. After fusion continue to heat till globules appear.
When cold, pick out the largest globule and test its malleability
on the anvil.

(c) Heat some zinc oxide with fusion mixture on charcoal with
the blowpipe. Note the color of the flame and the color of the
incrustation around the pit while hot and when cold. Moisten
the incrustation with a few drops of a dilute solution of cobalt
nitrate and heat again. Note the color of the mass.

TABLE IV BEHAVIOR OF SUBSTANCES HEATED ON
CHARCOAL ALONE



1. Substance deflagrates

2. Substance fuses and is absorbed in charcoal

3. Substance is infusible and incandescent .

4. When infusible, as in 3, treat with cobalt

nitrate and heat :
(a) Blue



(b) Green

(c) Pink

5. Substance leaves incrustation :

(a) White with garlic odor . .

(b) White without odor . . .



(c) Yellow (hot), white (cold)

(d) Brown



Nitrates, chlorates.
Alkali salts.
Alkali-earth and

earth salts.



Aluminum oxide

and phosphates.
Zinc oxide.
Magnesium oxide.

Arsenic compounds.
Ammonium and
mercury com-
pounds.
Zinc oxide.
Cadmium oxide.



METHODS OF ANALYTICAL SEPARATION 49



TABLE V BEHAVIOR OF SUBSTANCES HEATED ON
CHARCOAL WITH FLUX



1. A metallic bead is left :
(a) Soft and malleable and leaves yellow incrusta-
tion . . .


Lead


(6) Soft and malleable and leaves white incrusta-
tion . .


Tin.


(c) Hard and malleable and leaves no incrustation
(d) Hard and brittle and leaves white incrustation
(e) Hard and brittle and leaves yellow incrusta-


Silver.
Antimony.

Bismuth.


2 Magnetic particles


flron.
\ Nickel


3 Red particles


[Cobalt.
Copper.


4. When the moistened fused mass blackens a silver
coin


Sulphur
compounds.







CHAPTER IV

FLAME COLORATION AND SPECTROSCOPY

Light and Color. Light is due to vibrations of the ether,
of great velocity, in directions perpendicular to the path
of the light, and of frequencies which are inversely pro-
portional to the lengths of the ether waves. The vibra-
tions of lowest frequency and greatest length give rise
to light of a red color. With increasing frequency, the
color changes successively to orange, yellow, green, blue,
and violet, the last tint being due to the shortest vibra-
tions which can produce any effect upon the eye. Ordi-
nary white light such as is emitted by the sun, by the
glowing carbon of a flame or electric lamp, or by the in-
candescent mantle of the so-called " Welsbach burner "
is made up of vibrations of all lengths, the particular
quality of the light being dependent on the proportions in
which the vibrations of different lengths are mingled.

All incandescent solids emit a white light whose char-
acter is dependent upon their temperature rather than on
their nature; and hence we cannot well characterize
solids by their appearance when incandescent. Gases and
vapors, on the other hand, present distinctive colors when
heated to the point of incandescence, and they may be
identified by means of their color characteristics.

Flame Colorations. These colors may be readily observed
in the following manner : a platinum wire, bent into a

50



FLAME COLORATION AND 8PECTEOSCOPY 51

small loop at one end, and fixed in a handle of glass rod
at the other, is dipped into a strong solution of the material
whose vapor color is to be investigated, and is then held
in the non-luminous flame of a Bunsen lamp. According
to the nature of the material, the portion of the flame
above the wire may be colored more or less intensely.
Common salt, so treated, imparts a brilliant yellow hue
to the flame ; all other salts of sodium behave in similar
fashion, and therefore this "flame," being given by
no other substances, is taken as being characteristic of
sodium. Treated similarly, potassium compounds pro-
duce a violet coloration, calcium salts a yellowish
red, etc.

Experiment 17

Guided by the above description, confirm the following state-
ment regarding flame colorations :

TABLE VI SIMPLE FLAME COLORATIONS



1. Yellow, obscured by blue glass 1 .
2. Violet, not obscured by blue glass . . .
3 Carmine-red


Sodium salts.
Potassium salts.
Lithium salts


4. Yellow-red
5. Deep red . ....


Calcium salts.
Strontium salts


6. Green .


( Barium salts,
s Copper salts


7. Blue


[ Boric acid.
{Lead salts.
Arsenic




compounds.
Copper chloride.



1 The violet flame of potassium salts is so much less luminous than the
sodium flame that the naked eye may fail to detect it in presence of the
latter. But whereas the sodium flame is mostly obscured when viewed



52 CHEMICAL ANALYSIS

Spectroscopy. The vibrations of which we assume
light to be made up follow one another through the
ether in perfectly straight lines so long as their paths
are not obstructed. A line of such vibrations we call
a ray ; a group of parallel rays, a beam. When the
path of ray or beam is obstructed, a variety of things
may happen according to the nature of the obstruction.
In case the obstruction is pervious to the passage of
the ray, a portion of the vibrations may be reflected,
and the remainder will pass on through the obstruction.
Such rays as have met the surface of the latter exactly
at right angles will pass straight on; but any which
have met it obliquely may be more or less deflected or
refracted from the prolongation of their former path.
The degree of this refraction will be governed :

(1) by the relation between the optical " densities "
of the media through which the ray is passed ;

(2) by the vibration frequency or " wave length " of
the ray.

When a beam of white light is passed obliquely from
the air into a denser material, such as glass, there will
be a dispersion of its rays, those of the shortest wave
lengths being bent most from their original direction,
so that the former beam of parallel rays will be spread
out into a wedge of colored light, progressing from
red at one edge to violet at the other. When the
glass is in the form of a triangular prism, the disper-
sion will be most perfect; and with the help of such

through a slide of cobalt glass, that of potassium is very slightly dimmed.
Accordingly, when sodium is present, it is always necessary to examine
the flame for potassium with the aid of the blue glass.



FLAME COLORATION AND SPECTROSCOPY 53

a prism, we may study the character of light from any
source. Obviously, if our light is white, it will be
dispersed into a continuous band or " spectrum " ; if it
is colored, we shall have strips of color whose character
will indicate the composition of the light under exami-
nation. If our beam is entirely made up of vibrations
of only a few frequencies, we shall have a spectrum
consisting of a few bright lines.

Spectra can also be produced by gratings of numer-
ous thin parallel wires or of fine parallel etchings on
glass or metal. If light from a narrow slit is viewed
through gratings parallel with the slit, some of the
light can be seen to pass unaffected while part of it
produces a colored spectrum on each side of the grat-
ing. Spectra thus produced are due to diffraction.

The Spectroscope. Two classes of instruments depend-
ing, respectively, on refraction and diffraction are used
for the analysis of light. Each class has its advantages
and disadvantages. The prism spectroscope produces
brighter spectra, as only a small portion of the light is
lost by reflection and absorption. In the case of the
grating spectroscope, some light passes unaffected be-
tween the gratings, some is destroyed by interference,
and only the remainder is diffracted.

For accuracy the grating spectroscope is preferable
for two reasons : first, the dispersions of the rays in
grating spectra are directly proportional, while those of
the prism spectra are inversely proportional to the wave
lengths ; and, second, the lengths of the prism spectra
are dependent on the material of the prism, which
accounts for the fact that no two prisms give uniform



54 CHEMICAL ANALYSIS

dispersions. But the prism spectroscope, though less
accurate for technical physical work, is simpler and
better adapted to ordinary chemical analysis.

A simple form of the prism spectroscope consists of
a refracting prism, or set of prisms, and three small
telescopes mounted on a metal tripod. One of the tele-
scopes, called the collimator, has at one end a vertical slit
of adjustable width. The rays of light, having passed
through the slit and been rendered parallel by the lens
of the collimator, are refracted and dispersed by the
prism ; and the resulting spectrum is observed through
the eyepiece of the second telescope. The third tele-
scope contains a horizontal millimeter scale reduced
about one-fifteenth. Light from a white flame, placed
in front of the scale telescope, passes through the scale
and is reflected on that face of the prism which stands
before the eye telescope, so that both the image from
the collimator and that from the scale are seen at the
same place.

Another form of .this type of instrument is the direct-
vision spectroscope, in which one telescope is used for
both the eyepiece and collimator, the prisms being
placed within it. The Janssen direct-vision tele-
scope, 1 made by the Geneva Society, contains also a
scale telescope.

Kinds of Spectra. The spectroscope shows three kinds
of spectra : -

1. The Continuous Spectrum, produced by a white-
hot solid or liquid. Solids and liquids emit rays of
many wave lengths and thus give the colors blended
in the order of their wave lengths. A platinum wire



FLAME COLORATION AND SPECTROSCOPY 55

heated to whiteness in a non-luminous flame shows a
continuous spectrum in the spectroscope.

2. The Discontinuous Spectrum, produced by an in-
candescent gas or vapor. Gases and vapors emit rays
of few wave lengths, and ' hence the spectrum shows
only certain bright lines or bands. A platinum wire
dipped in a paste of common salt and hydrochloric acid,
and heated in a non-luminous flame, shows, in addition
to the continuous spectrum of the white-hot wire, a
bright yellow line produced by the vapors of the salt.

3. The Absorption Spectrum, produced by an incan-
descent solid or liquid which is viewed through a
gaseous or liquid medium. The medium absorbs the

.rays peculiar to itself, and thus produces certain dark
lines in the continuous spectrum. The so-called Frauen-
hofer's lines dark bands which cross the solar spec-
trum are caused by the absorption of rays emitted from
the interior mass of the sun in their passage through an
exterior gaseous envelope. Similarly, in the same way,
white light passed through a solution of potassium
permanganate gives a spectrum deprived of the yellow,
green, and blue rays, in whose places are seen dark
bands.

Flame Spectra. - - Those solids which vaporize at the
temperature of a Bunsen flame can easily be examined
in the flame. They are the salts of the alkali and the
alkali-earth metals. A blank analysis should first be
made by holding a clean platinum wire in the dark
flame about 2 cm. before the collimator slit. By focus-
ing the telescopes and darkening the room, a dim
yellow line will be observed, due to the presence of



56 CHEMICAL ANALYSIS

sodium compounds in the atmosphere. This may be
expected in all spectra.

For convenience, it is customary to regulate the scale
so that the left-hand margin of the yellow sodium line
will exactly coincide with 50. 1 For analysis a thin
paste of the salt is supported by a small loop on a
platinum wire and held in the non-luminous flame
before the collimator slit.

Spark Spectra. Those solids which are vaporized not
by a simple flame, but by an electric spark, include a
large majority of the elements and compounds. The
spectra of gases are also produced by the electric spark,
which can be made by an induction coil or influence
machine.

For ordinary analyses, a good apparatus consists of
a 3-inch spark coil charged with a storage battery of
three or five cells. Primary cells are either too weak or
too inconstant. The voltage of the coil can be
increased by passing the positive pole through
a Leyden jar. A support for the substance to
be analyzed, such as is represented by the cut,
can be made by fusing the end of a platinum
wire 4cm. long into one end of a small, thin
glass tube 1cm. in diameter, so that the wire
will stand free on the inside of the tube about
2cm. from the closed end. Cut the tube so
that the edge of the little cup will stand about
1mm. above the end of the wire. Draw out another
piece of thin tubing to a capillary about the length of
the inside wire. A number of these cups should be made
and kept ready for use in a test-tube of distilled water.






FLAME COLORATION AND SPECTROSCOPY 57

In using this apparatus, first connect the empty cup

to the negative pole of the coil by means of a small

j U-tube filled with mercury. Clamp the positive plati-

i num tipped pole above the cup so that the two poles

1 will be about 1mm. apart. Close 1 the circuit and make

a blank analysis with the spectroscope. Certain bright

lines representing the spectra of the gases of the air

are often seen. In order to avoid error in subsequent

analyses for spark spectra, the presence of these lines

should be anticipated. Fill the cup about one-third

full of a strong solution of the substance to be analyzed,

close the circuit, and examine the spectrum.

Absorption Spectra. Solutions of many substances,
both inorganic and organic, and also many gases, give
characteristic absorption spectra.

The solvents are various, though water and alcohol
are most common. This method not only confirms
many line spectra of inorganic compounds, but also
affords the only means of spectrum analysis for com-
pounds decomposed by heat. Among the inorganic
bodies whose absorption spectra are important to the
analyst are the salts of aluminum, iron, cobalt, nickel,
arid manganese. The most important among organic
compounds are the dyes, blood, chlorophyll, etc.

The apparatus necessary for producing absorption
spectra is the spectroscope, a white light, and a large
test-tube to contain the solution to be examined. First
arrange the spectroscope as for flame or spark spectra,
and then place the white light about 2 dm. in front of
the collimator slit so that a clear continuous spectrum
will appear. Interpose between the slit and the white



58



CHEMICAL ANALYSIS



- *



rt-



i









FLAME COLORATION AND SPECTEOSCOPY 59



\>

*

h



60 CHEMICAL ANALYSIS



EXPLANATION OF TABLE VII

Nos. 1, 2, 3, 4, 5, and 6 represent the discontinuous spectra of
salts of metals volatile in the flame. The lines and curves in the
I field of each spectrum indicate the position and distinctness of
visible lines. For example, the spectrum of potassium appears
on the scale as a strong line between 10 and 20, more accurately
17, and another thinner and shorter line between 150 and 160,
more accurately 154. The long curve from 20 to 130 shows
that there are many indistinct lines within that area, and the
varying heights of the curve indicate the relative distinctness of
the lines.

Nos. 7, 8, and 9 represent the discontinuous spectra of salts of
metals volatilized by the electric spark. Spark spectra are char-
acterized by the small number of narrow lines and the absence
of indistinct lines. No. 10 represents the absorption spectrum of
* sunlight, showing the so-called Fraunhofer's lines.

Nos. 11, 12, 13, 14, 15, and 16 represent absorption spectra.
The shaded parts show the portion of the spectrum absorbed, arid
the curved margins the relative degrees of absorption.



FLAME COLORATION AND SPECTROSCOPY 61

light the test-tube filled with a dilute solution of the
substance. Certain portions of the continuous spectrum
will now appear dark.

Mapping Spectra. Two methods have been adopted
for recording spectra :

1. Kirchoff and Bunsen's scale, 1 by which the posi-
tions of the lines are recorded on a graduated scale.
The conventional practice is to adjust the scale so that
the yellow sodium line shall coincide with 50 on the
scale. This method is quite simple, and though not so
accurate as the other method, it is generally used for
chemical analysis.

2. The wave-length method, by which the wave
lengths of the colors are calculated from the formula

v
\ = -, in which X, v, and n, respectively, are wave length,

velocity of light, and number of vibrations. The unit is
one ten-millionth of a millimeter, called an Angstrom.

Professor Rowland of Johns Hopkins University, by
means of his improved concave grating spectroscope,
has compiled an atlas 2 of a large number of spectra
recorded in wave lengths. In this elementary book
measurements of wave lengths would not be consistent
with the character of the work. Hence the use of
Kirchoff and Bunsen's scale is recommended.

The table on pages 58 and 59 includes some illustra-
tions of a method of mapping spectra.

Experiment 18

(a) Examine and map the flame spectra of the following
salts: sodium chloride, potassium chloride, lithium chloride,
barium chloride, strontium chloride, and calcium chloride.



62 CHEMICAL ANALYSIS

(6) Examine and map the spark spectra of the following
salts: magnesium chloride, zinc chloride, manganese chloride,
copper chloride, and bismuth chloride.

(c) Examine and map the absorption spectra of the follow-
ing inorganic salts : ferric chloride in water, potassium perman-
ganate in water, chrome alum in water, and cobalt nitrate in
alcohol.

(d) Examine and map the absorption spectra of alcoholic solu-
tions of blood and fuchsine, and a water solution of logwood.

Special Method for Aluminum (Vogel). Make a solution
of extract of logwood by boiling the chips in water.
Place a test-tube containing this extract between the
spectroscope and a luminous flame. The right end of
the spectrum will be absorbed, the extent of absorption
depending on the concentration of the logwood. The
boundary between the absorbed and unabsorbed parts
of the spectrum is made to coincide with a convenient
line on the scale. Now add a few drops of a dilute
neutral solution of an aluminum salt. This will cause
the boundary line to move to the left in proportion to
the concentration of the solution. The aluminum salt
solution is made neutral by adding to it, drop by drop,
a very dilute solution of ammonia, until a slight but
permanent precipitate is produced.

Neutral ferric salts give the same reaction, but iron
can be tested for in the wet way. In case of a mixture
of aluminum and iron salts, the iron can be removed
by adding an excess of ammonium sulphocyanate
solution and shaking out the ferric sulphocyanate
with ether. The colorless aqueous portion is tested
for aluminum salts. (See Nos. 13 and 14 on the
table.)



FLAME COLORATION AND SPECTROSCOPY 63


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