properties of arsenic and antimony need not be repeated here. The search
for antimony is likewise executed by aid of Marsh's apparatus. We will
confine ourselves to a description of a modification to this apparatus
proposed by _MM. Flandin_ and _Danger_, and employed in the separation
of antimony and arsenic, when a mixture of these metals is under
examination. Another process, by means of which we arrive at the same
result with greater certainty and by the use of a less expensive
apparatus, will then be mentioned. We will, however, first indicate the
preferable method of destruction of the organic substances.
Were the decomposition performed by means of sulphuric acid, sulphate of
antimony, a slightly soluble salt and one not well adapted to the
subsequent treatment with nascent hydrogen, would be formed. In order to
obtain the metal in a soluble state, the formation of a double tartrate
of antimony and soda is desirable. This may be accomplished in the
following manner:
1. A cold mixture of nitrate of soda, sulphuric acid, and the suspected
materials is prepared in the proportion of 25 grammes of the nitrate to
39 grammes of the acid, and 100 grammes of the substance under
examination. This mixture is heated and evaporated to dryness, and the
decomposition of the organic matter completed in the usual manner. The
carbonaceous residue obtained is pulverized, and then boiled with a
solution of tartaric acid. By this treatment the antimonate of soda
present is converted into a double tartrate of antimony and soda, which
is easily soluble in water. The solution is filtered and then introduced
into Marsh's apparatus.
2. Another method consists in heating the substances under examination
with one half of their weight of hydrochloric acid for six hours on a
sand-bath, avoiding boiling. The temperature is then increased until the
liquid is in a state of ebullition, and 15 to 20 grammes of chlorate of
potassa, for every 100 grammes of the suspected matter taken, added in
successive portions, so that a quarter of an hour is required for the
operation. The liquid is next filtered, and the resinous matter
remaining on the filter well washed with distilled water; the washings
being added to the principal solution. A strip of polished tin is then
immersed in the liquid: in presence of a large amount of antimony the
tin becomes covered with a black incrustation: if but a minute quantity
of the metal is contained, only a few blackish spots are perceptible.
After the tin has remained immersed for 24 hours, it is withdrawn and
placed in a flask together with an amount of hydrochloric acid
sufficient for its solution in the cold. If, after several hours,
blackish particles are still observed floating in the liquid, they can
be dissolved in a few drops of _aqua regia_. The solution may then be
directly introduced into Marsh's apparatus.
APPARATUS PROPOSED BY FLANDIN AND DANGER.
[Illustration: Fig. 7.]
This apparatus consists of a wide necked jar _A_ (Fig. 7) for the
generation of the gas, the mouth of which is closed with a cork having
two openings. The safety tube _S_, which is funnel-shaped at its upper
extremity and has its lower end drawn out to a point, passes through one
of these apertures; the other opening contains the small delivery tube
_B_, open at both ends, and terminating in a point at its upper
extremity: it is also provided with lateral openings, in order to
prevent the solution being carried up to the flame. The second part of
the apparatus is the condenser _C_, 0.03 metre in diameter, and 0.25
metre in length. This terminates at its lower extremity with a cone, and
connects at the side with the tube _T_, slanting slightly downwards. In
the interior of the condenser, the cooler _E_ is contained, the lower
end of which is nearly in contact with the sides of the opening _O_. The
combustion tube _D_, 0.01 metre in diameter, is connected by means of a
cork with the tube _T_; it is bent at right angles, and encloses the
tube _B_, in such a manner as to allow the evolved gas to burn in its
interior. The dish _F_ is placed beneath the opening _O_. If the gas
which burns in the combustion tube contains arsenetted hydrogen, water
and arsenious acid are produced. A portion of this acid is retained in
the tube _D_, the remainder is carried over, with the aqueous vapor,
into _C_, where it condenses, and finally falls into the dish _F_. Both
portions are subsequently examined by means of reactions necessary to
establish the presence of the acid. If the ignited gas contains
antimonetted hydrogen, water and an intermediate oxide of antimony are
formed. The latter compound is entirely retained in the tube _D_
separated from the greater part of the arsenious acid, if this body be
present, and can be brought into solution by means of a mixture of
hydrochloric and tartaric acids. A fluid is then obtained which can be
introduced into Marsh's apparatus, or otherwise examined for antimony.
NAQUET'S APPARATUS.
[Illustration: Fig. 8.]
Although the separation of arsenic from antimony is the chief object in
making use of the apparatus proposed by Flandin and Danger, it is
evident that this result is not fully accomplished, since a small
portion of arsenious acid remains in the tube _D_ (Fig. 7), together
with the intermediate oxide of antimony. The following method secures
the complete separation of these metals: An amalgam of sodium and
mercury is introduced into the flask _A_, (Fig. 8), which is provided
with two openings. The tube _B_, terminating in a funnel at its upper
extremity, passes through one of these orifices. The other aperture
contains a cork enclosing the small tube _C_, which is bent at a right
angle and communicates, by means of a cork, with the larger tube _D_
filled with cotton or asbestus. A set of Liebig's bulbs, _E_, containing
a solution of nitrate of silver, is attached to the other extremity of
this tube. The apparatus being mounted, the solution under examination
is slightly acidulated and introduced by means of the tube _B_ into the
flask _A_: the disengagement of gas begins immediately. If arsenic and
antimony are contained in the solution, arsenetted hydrogen and
antimonetted hydrogen are evolved. Both gases are decomposed in passing
through the solution of nitrate of silver contained in the Liebig bulbs:
the arsenetted hydrogen causes a precipitation of metallic silver, all
the arsenic remaining in solution as arsenious acid; the antimonetted
hydrogen is decomposed into insoluble antimonate of silver. After the
operation has continued for several hours, the apparatus is taken apart,
the nitrate of silver solution thrown on a filter, and the precipitate
thoroughly washed. An excess of hydrochloric acid is then added to the
filtrate, and the precipitate formed separated from the solution by
filtration, and well washed. The wash-water is added to the solution,
and the whole then examined for arsenic by means of Marsh's test.
The precipitate formed in the nitrate of silver solution, which
contains antimonate of silver, is well dried, mixed with a mixture of
carbonate and nitrate of soda, and calcined in a porcelain crucible for
about three-quarters of an hour. The crucible is then removed from the
fire, and the cooled mass treated with hydrochloric acid until a drop of
the filtered fluid ceases to give a residue when evaporated upon a
watch-glass to dryness. A current of sulphurous acid is now conducted
through the filtered solution until the odor of this gas remains
persistent. The excess of acid is then removed by boiling, and the
solution placed in Marsh's apparatus and tested for antimony.
DETECTION OF MERCURY.
If a mercurial salt exists in a considerable quantity in the substances
extracted from the alimentary canal, or ejected either by stools or
vomiting, it can be isolated by treating these materials with water,
filtering the liquid, and evaporating the filtrate to dryness. The
residual mass is taken up with alcohol, and the solution again filtered
and evaporated. Upon dissolving the residue obtained by this operation
in ether and filtering and evaporating the solution, a residue is
obtained which when dissolved in water forms a fluid wherein the
presence of mercury can be detected by means of the ordinary tests.
When, however, only a minute quantity of mercury is present, and this
has been absorbed, its detection is more difficult. It will be necessary
under these circumstances to make use of either Smithson's pile or
Flandin and Danger's apparatus.
SMITHSON'S PILE.
Smithson's pile consists of a small plate of copper around which a
piece of thin gold foil is wrapped. This is immersed in the solution to
be tested for mercury, which has previously been slightly acidulated: if
mercury be present, the plate acquires a white color which disappears
upon exposure to the flame of a spirit-lamp. A similar reaction occurs
in presence of tin, as this metal would likewise be deposited upon the
plate, and, upon heating, would penetrate the metal and restore to it
its natural color. The danger of mistake arising from this fact is
obviated by introducing the copper plate into a tube closed at one end
and bent at a right angle. The open extremity of the tube is drawn out
to a fine point and immersed in water contained in a second tube also
closed at one end. Upon heating the plate in the flame of an alcohol
lamp, the white color disappears if produced by mercury, and at the same
time this metal condenses in the narrow extremity of the tube. The
metallic globules formed can be recognized either by the naked eye or
with the aid of a lens, or by rubbing them with a piece of gold foil
when the latter will acquire a white coating.
When Smithson's pile is employed, the organic substances are most
advantageously decomposed by means of chlorine. It is advisable to
operate with as small a quantity of fluid as possible, for, owing to the
volatility of bichloride of mercury, a portion of this salt may be lost
by the evaporation of aqueous, alcoholic, and even etherial solutions,
and the detection of minute quantities rendered impossible.
APPARATUS PROPOSED BY FLANDIN AND DANGER.
[Illustration: Fig. 9.]
This apparatus consists of a stand _S_, (Fig. 9) supporting a balloon
_A_, which serves as the reservoir of the suspected solution, and a
funnel _B_, into which the neck of the balloon is dipped. The funnel _B_
is bent at a right angle and is drawn out at its lower end under which
the dish _C_ is placed for the reception of the escaping fluids. A fine
wire of pure gold, forming the negative electrode of a Bunsen's battery,
passes through the lower extremity of the funnel. The end of this wire
nearly comes in contact with a second wire, inserted in the upper part
of the funnel, and connected with the positive pole of the battery. If
the balloon filled with the solution is inverted and immersed in the
funnel _B_, its neck will be submerged at first; soon, however, it
becomes uncovered, owing to the depression of the level of the fluid
caused by the escape of the latter through the tapering extremity of the
funnel: a bubble of air then passes in the balloon and expels a drop of
the solution. This process is repeated at short intervals, causing a
continuous flow of the fluid, the rapidity of which is easily regulated
by elevating or lowering the balloon, thus raising or depressing the
level of the liquid. The apparatus having been mounted in this manner
and the battery set in action, the disengagement of gas commences.
Should mercury be contained in the solution under examination, this
metal will be deposited upon the negative wire. When the operation is
completed this wire is detached from the apparatus, washed with ether,
and dried. It is then introduced into a small tube provided with a bulb,
and the mercury volatilized by means of the blow pipe flame: the metal
condenses in the bulb of the tube in globules which are readily
recognized. They can also be dissolved in nitric acid, and the presence
of a mercurial salt in the solution confirmed by further tests.
The solution to be examined in the preceding apparatus, is prepared as
follows:
The suspected organic matter is treated with cold sulphuric acid of 66°
_B._ until liquefied, and hypochlorite of lime, and distilled water then
added: if necessary, the evolution of chlorine can be accelerated by a
further addition of sulphuric acid. As soon as the liquid becomes clear,
it is filtered, concentrated and examined as described above. The
solution contains the mercury in the state of bichloride, a salt soluble
in water and well adapted to the above test.
The substitution of a large balloon, having a capacity of about 2
litres, in place of the small vessel of Flandin and Danger's apparatus,
is to be recommended as doing away with the necessity of evaporation; an
operation which invariably causes a loss of substance. The apparatus,
modified in this manner, is the most delicate in use for the detection
of mercury.
DETECTION OF PHOSPHORUS.
ORFILA'S METHOD.
The solid substances found in the alimentary canal are mechanically
separated from the fluids present by means of a linen cloth. They are
then examined by aid of a magnifying glass, and any fragments of
phosphorus found separated and preserved under water. If none are
discovered, the presence of phosphorescent vapors may possibly be
detected by examining the materials in the dark. In any case, a portion
of the suspected materials should be treated with nitrate of silver: in
presence of phosphorus the materials acquire, first, a reddish-brown,
then, a black color. The remaining portion is spread upon a shovel and
heated: a white flame, burning at various points of the mass, and
originating from the combustion of phosphorus, is observed, if this body
be contained in the substances under examination. This method is
evidently far from perfect.
MITSCHERLICH'S METHOD.
Mistcherlich's method is based upon the luminosity of the vapors of
phosphorus. The suspected materials are moistened with dilute sulphuric
acid, and heated, in a flask communicating with a glass worm which
passes through a glass cooler into a receiver. If the apparatus is
placed in the dark, and the materials contain phosphorus, luminous
vapors will be observed in the flask and receiver. When the quantity of
the poison present is considerable, the phosphorous acid formed can be
collected and its properties tested.
DUSART'S METHOD, AS MODIFIED BY BLONDLOT.
[Illustration: Fig. 10.]
Dusart's process takes advantage of the facility with which hydrogen
combines with phosphorus. The substances under examination are placed
between two asbestus stoppers in a tube, one end of which tapers to a
point, and a current of pure hydrogen conducted over them. In presence
of phosphorus the evolved gas will burn with a green flame, and, upon
bringing this in contact with a porcelain plate, red spots will be
deposited upon the latter. _Blondlot_ prefers to introduce the suspected
materials into the flask in which the hydrogen is generated. He employs
the apparatus represented in Fig. 10: _a_ is a flask for evolving
hydrogen; _b_ is a U tube, filled with fragments of pumice stone which
are saturated with a concentrated solution of potassa; _c_ is a Mohr
clamp; _d_ a screw-clamp; _e_ a platinum jet. This jet is necessary in
order to avoid a yellow coloration of the flame by the soda contained in
the glass. Pure hydrogen is at first evolved, in order to ascertain that
the flame is colorless and red spots are not produced when it is
intersected by a cold plate. The purity of the reagents used having thus
been confirmed, the clamp _d_ is closed until the acid is forced back
into _f_; and the materials to be examined are then added to the fluid.
Upon opening the clamp the liquid passes from _f_ into _a_, and the
evolution of gas recommences. The gas is then ignited: the flame
possesses the characteristic properties mentioned above, if the
suspected substances contain phosphorus.
METHOD PROPOSED BY FRESENIUS AND NEUBAUER.
According to this method, the materials are brought into a flask
provided with a doubly-perforated stopper, and water, acidulated with
sulphuric acid, added. The flask is then heated over a water-bath, and a
current of carbonic acid conducted through the mixture for at least two
hours. The gas, on leaving the flask, passes into a solution of nitrate
of silver. Should no precipitate form in this solution, the absence of
free phosphorus is established, for, were this body present, a portion
would be volatilized, and a black precipitate, consisting of phosphide
of silver, together with phosphoric acid, produced. The formation of a
black precipitate is, however, not necessarily a proof of the presence
of phosphorus. In order to conclusively determine the character of the
precipitate, it is collected on a filter and examined by the method of
Dusart and Blondlot.
This process has given result in cases where none were obtained by
Mistcherlich's method. It possesses, moreover, an advantage over the
latter process, in not being influenced by the presence of foreign
bodies; whereas, in Mistcherlich's method, some time must elapse before
the luminosity of the vapors becomes apparent if ether or alcohol is
contained in the solutions, and this phenomenon totally fails to appear
in presence of oil of turpentine.
DETECTION OF PHOSPHORUS BY THE USE OF BISULPHIDE OF CARBON.
In a report read before the Academy of Sciences in 1856, presented by an
examining commission, of which MM. _Dumas_, _Pelouze_ and _Claude
Bernard_ were the reporters, the following results were contained:
Phosphorus may remain, in the _free state_, in the organs fifteen days
after death, and even then its isolation can easily be accomplished. For
this purpose the stomach or intestines, and the articles of food
contained therein, are cut into pieces and treated with bisulphide of
carbon. Upon filtering the liquid, a solution is obtained containing all
the phosphorus present, which exhibits the following properties: 1st,
When ignited, it burns with a very luminous flame; 2nd, if allowed to
spontaneously evaporate (the combustion of the phosphorus being
prevented by the organic matter present [_Naquet_]) an inflammable
residue is obtained, which, if dissolved in boiling monohydrated nitric
acid, gives a solution that, after saturation with ammonia, produces a
precipitate soluble in acids in solutions of barium salts. If the
solution is mixed with perchloride of iron, and the sesquioxide of this
metal subsequently eliminated by the addition of ammonia, it no longer
causes a precipitation in barium solutions. The fluid acquires a yellow
coloration when boiled with a solution of molybdate of ammonia.
According to our personal experience, the apparatus employed by Flandin
and Danger for the detection of arsenic, can also be made use of in the
examination of the bisulphide of carbon solution. To this end, the fluid
supposed to contain phosphorus is mixed with perfectly pure alcohol, and
the mixture placed in a small spirit-lamp provided with a very loose
asbestus wick. The lamp is then ignited and the flame introduced in the
combustion tube _D_ (Fig. 11).
[Illustration: Fig. 11.]
By the combustion of the mixture, sulphurous, carbonic, phosphorous
acids and water are formed. The water condenses in _c_, and, falling
into the dish _F_, carries with it the sulphurous and phosphorous acids.
The acid liquid collected in this way is evaporated to dryness, some
nitric acid added, and the solution again evaporated. The remaining mass
is then dissolved in water to which some ammonia is added, and the
solution tested for phosphoric acid. This method is an advantageous one
as the phosphoric acid formed must originate from phosphorus in the
_free state_, and not from any phosphates which, owing to the presence
of organic matter, might be contained in the bisulphide of carbon
solution. It would, however, lead the analyst into error if the person,
supposed to have been poisoned had eaten cerebral substances or eggs
previous to death, as these contain glycero-phosphoric acid; it is
therefore advisable to compare the results given by this process with
those obtained by the use of other methods.
DETECTION OF PHOSPHOROUS ACID.
Provided free phosphorus has not been detected, it is necessary to
search for phosphorous acid. To this end, the residue remaining in the
flask, in either Mistcherlich's or Fresenius and Neubauer's method, is
introduced into the apparatus of Dusard and Blondlot. If the phosphorus
reaction appears, it is sufficient; otherwise, its production may have
been hindered by the presence of organic matter. In case, therefore, the
flame is colorless, the evolved gas is conducted into a neutral solution
of nitrate of silver. If the materials contain phosphorous acid, a
precipitate of phosphide of silver is formed which should be collected
and washed. The precipitate, which is now free from organic matter, is
then examined for phosphorous acid by means of the apparatus of Dusard
and Blondlot.
ESTIMATION OF PHOSPHORUS.
The best process for determining quantitatively the amount of
phosphorus present is the one recommended by Fresenius and Neubauer. The
gaseous current is continued until a fresh nitrate of silver solution is
no longer precipitated. The solution is filtered, the precipitate washed
and then dissolved in nitric acid. The silver is next precipitated by
addition of hydrochloric acid, the fluid again filtered, and the
precipitate well washed. The washings are added to the filtrate, and the
liquid concentrated in a porcelain capsule. A solution of sulphate of
magnesia, containing ammonia, is next added to the fluid, and the
phosphoric acid determined as pyrophosphate of magnesia: the precipitate
formed, is washed, heated to redness, in order to convert it into the
pyrophosphate, and then weighed.
DETECTION OF ACIDS.
The search for acids is to be instituted exclusively in the alimentary
canal and its contents. Were acids contained in the other organs, their
presence would be due to the blood in which they had previously been
absorbed, and, as in this case they would be partially neutralized by
the bases contained in the blood, a conclusive decision in regard to
their original existence in the suspected materials would be impossible,
the salts of the acids usually searched for being normal constituents of
the blood. In order to detect the presence of acids, the alimentary
canal and contents are first boiled with water which is renewed until
the solution ceases to exhibit an acid reaction when tested with litmus
paper. The fluid is then filtered, alcohol added to the filtrate, in
order to precipitate organic substances, the liquid again filtered, and
the solution tested separately for the various acids as directed below.
HYDROCHLORIC ACID.
The solution is placed in a retort provided with a receiver and
distilled until the residual fluid assumes a pasty consistence: the
operation is then discontinued. If hydrochloric acid be present in the
materials under examination, the distillate will have an acid reaction,
and, upon addition of solution of nitrate of silver, a white
precipitate, which is easily soluble in ammonia but insoluble in nitric
acid and in short possesses all the properties of chloride of silver,
will be formed.
NITRIC ACID.
The distillate, obtained as in the preceding process, is neutralized by
the addition of potassa or soda, and evaporated to dryness. The residue
is mixed with copper filings, and introduced into a glass tube closed at
one end and provided at the other with a cork through which a
delivery-tube passes. Sulphuric acid is then added to the mixture, the
cork inserted, the tube heated, and the evolved vapors conducted into a
solution of protosulphate of iron. The latter solution acquires a brown
coloration which, upon addition of sulphuric acid, changes to a violet,
if nitric acid be present. Upon conducting the disengaged gas into a
solution of narcotine, the latter acquires a beautiful red color.
Another portion of the residue should deflagrate when saturated with an
alkali and projected upon live coals.
SULPHURIC ACID.