organs with water is not distilled but is concentrated to one-sixth of
its original volume, and then agitated with ether for about ten minutes.
By this treatment the ether takes up the free sulphuric acid, but not
the acid sulphates present. After ten minutes contact, the ether is
decanted and allowed to spontaneously evaporate. Upon treating the
residue, which contains the free sulphuric acid and fatty substances,
with water, a solution containing only the sulphuric acid is obtained.
Nitrate of baryta is then added to a portion of the fluid: in presence
of sulphuric acid, a white precipitate, insoluble in acids, is produced.
If this is heated on charcoal before the blow-pipe, a mass is formed,
which, when moistened with hydrochloric acid and placed upon a clean
silver coin, produces a black spot on the metal. Another portion of the
solution is mixed with copper and the mixture evaporated in a tube
closed at one end: sulphurous acid is evolved towards the end of the
operation. This gas is detected by allowing it to pass over paper
saturated with a mixture of iodic acid and starch; a blue coloration is
produced which, owing to the transformation of the iodine set free into
hydriodic acid, subsequently disappears. (We have never been able to
effect the disengagement of sulphurous acid spoken of above when an
exceedingly dilute sulphuric acid was used, even upon evaporating the
mixture to dryness, notwithstanding Orfila's statement that the reaction
occurs very readily.)
PHOSPHORIC ACID.
The aqueous solution is evaporated to dryness, the residue taken up
with alcohol of 44° B., the fluid again evaporated, and the second
residue dissolved in water. Upon adding acetate of lead to the solution,
a white precipitate is produced if phosphoric acid be present. The
precipitate is washed, suspended in water and a current of sulphuretted
hydrogen passed through the mixture. If the fluid is then filtered, and
the excess of sulphuretted hydrogen expelled from the filtrate by
boiling, a liquid possessing the distinctive properties of a solution of
phosphoric acid will be obtained. This should then be submitted to the
following tests: Some pulverized charcoal is added to a portion of the
solution, the mixture evaporated to dryness, and the residue obtained
introduced into a Hessian crucible heated to redness: in presence of a
considerable amount of the acid, free phosphorous is liberated and burns
with a bright flame in the upper part of the crucible. In case this
reaction fails to occur, other portions of the fluid are treated with a
solution of a baryta salt, which causes a white precipitate, soluble in
nitric acid; with an ammoniated solution of sulphate of magnesia, which
throws down a crystalline white precipitate; and by boiling with
molybdate of ammonia, acidulated with nitric acid, which produces a
yellow precipitation, or at least a yellow coloration of the solution.
OXALIC ACID.
The solution is subjected to the same treatment as in the search for
phosphoric acid, with the exception that, instead of adding acetate of
lead to the fluid obtained by taking up the residue left from the
alcohol with water, it is divided into two portions which are examined
separately. A solution of a lime salt is added to one portion: if oxalic
acid be present, a precipitate, which is insoluble in acetic acid or in
chloride of ammonium, and effervesces when slightly calcined and treated
with hydrochloric acid, is formed. Nitrate of silver is added to the
remaining portion of the solution: the formation of a precipitate, which
detonates when dried and heated in a glass tube closed at one end, is
further evidence of the presence of the acid.
ACETIC ACID.
The solution obtained by treating the alimentary canal with water is
distilled, as in testing for nitric and hydrochloric acids, and the
following properties verified in the distillate: 1st. It has an acid
reaction, and possesses the odor of vinegar; 2nd, unless previously
neutralized with a base, it fails to redden the per-salts of iron; 3rd,
if the distillate is added to a solution of the per-salts mentioned and
sulphuretted hydrogen conducted through the fluid, a black precipitate
is formed; 4th, upon boiling the still acid fluid with a small quantity
of starch, the property of the latter to become colored in presence of
free iodine is not changed; 5th, if heated with an excess of litharge, a
basic salt which restores the blue color to reddened litmus paper is
produced.
HYDROCYANIC ACID.
The detection of hydrocyanic acid requires special precautions. The
substances to be examined are mixed with water, if solids are present,
and introduced into a retort provided with a delivery-tube which dips in
a solution of nitrate of silver. The retort is then heated over a
water-bath. If the evolved vapors produce a precipitate in the silver
solution, the heating is continued until a fresh portion of the latter
is no longer affected. The operation is now interrupted, hydrochloric
acid added to the retort, and heat again applied. Should a second
precipitation of cyanide of silver occur, the presence of a _cyanide_ in
the suspected materials is indicated; whereas the formation of a
precipitate by the simple action of heat would point to the presence of
free hydrocyanic acid or cyanide of ammonium.[H] In case the latter
compound is present, ammonia will be contained in the distillate.
[H] Ferrocyanides and ferricyanides--non-poisonous
compounds--likewise, evolve hydrocyanic acid when distilled with a
strong acid. Their presence is indicated by stirring a small portion
of the materials with water, filtering the fluid, acidulating the
filtrate with hydrochloric acid, and testing two portions: one with
sesquichloride of iron, the other with protosulphate of iron. If
either of the above salts be present, a blue precipitate is
produced.--_Trans._
In order to identify the cyanogen, a portion of the precipitate is
collected upon a small filter, washed, dried, and then allowed to fall
into a rather long tube, closed at one end, in the bottom of which some
iodine has previously been placed. A column of carbonate of soda is then
introduced above the precipitate for the purpose of retaining the excess
of iodine probably taken. Upon heating the lower end of the tube, white
fumes of iodide of cyanogen, which condense in needles upon the cold
portion of the tube, are produced. These are easily recognized by aid of
a magnifying glass. They are colorless and are readily volatilized by
heat. Some ammonia is next added to a solution of protosulphate of iron,
the precipitate formed thoroughly washed, and exposed to the air until
it acquires a greenish hue. The iodide of cyanogen is then withdrawn
from the tube and mixed with potassa-lye and the precipitate mentioned
above. The mixture is evaporated to dryness, the residue obtained
treated with water and the filtered solution then acidulated with
hydrochloric acid. If a solution of a persalt of iron is now added to
the fluid, a blue precipitate is formed. The addition of salts of copper
produces a reddish precipitation.
The remainder of the precipitate formed in the nitrate of silver
solution is heated with sulphur and then boiled with an aqueous solution
of chloride of sodium: if cyanogen is contained in the precipitate, a
solution of sulphocyanate of soda will be formed, and upon adding
sesquichloride of iron an intense red coloration produced.
It is evident that the presence of another acid in the solution
examined for hydrocyanic acid would render the detection of _cyanides_
impossible, but in all cases hydrocyanic acid can be separated without
arriving at a decision in regard to its original state of combination.
Nitric, hydrochloric, and several other acids would not be distilled at
the temperature of the water-bath; an examination for these by the
methods already described can therefore be instituted simultaneously
with the search for hydrocyanic acid.
DETECTION OF ALKALIES AND ALKALINE EARTHS.
The separation of these bodies in the caustic state is a matter of
difficulty owing to the great tendency they possess to become converted
into carbonates; the carbonates of lime, baryta and strontia, moreover,
being non-poisonous in their effects, will not be employed with criminal
intent, and the carbonates of soda and potassa are extensively used as
pharmaceutical preparations. Notwithstanding the small chances of
success, the isolation of the compounds under consideration in the
caustic state is to be attempted.
To this intent, the organs to be analysed, together with their
contents, are placed in a glass retort provided with a receiver, water
added, and the mixture boiled. The distillate will contain the ammonia
present. When, however, putrefaction has begun, the detection of this
compound does not necessarily indicate its original presence in the
suspected materials. If, after an hour's boiling, the fluid in the
retort possess an alkaline reaction, it is to be examined for soda,
potassa, strontia, baryta and lime. The undistilled solution is
filtered, the filtrate evaporated to dryness, and the residual mass
treated with alcohol. By this treatment, potassa and soda go in
solution, lime, baryta and strontia[I]--as well as the alkaline
carbonates--remaining undissolved. The potassa and soda are separated
from the other salts present by filtering and evaporating the alcoholic
solution to dryness and then calcining the residue in a silver crucible.
The mass, which should still be alkaline, is then dissolved in dilute
sulphuric acid. If the solution is turbid, traces of baryta or strontia
may still be present and should be removed by filtration. Some
hydrochloric acid and solution of bichloride of platinum are then added
to a portion of the filtered liquid: in presence of _potassa_ a yellow
precipitate is formed.
[I] Baryta and strontia dissolve in alcohol, but only when they are
anhydrous and the alcohol is absolute, which is not the case here.
Another portion is treated with tartaric acid: a white granular
precipitate is produced. Hydrofluosilicic acid is added to a third
portion of the solution: the formation of a gelatinous precipitate is a
further indication of the presence of potassa. If the preceding tests
have given negative results, and a white precipitate is formed by the
addition of antimonate of potassa to another portion of the solution,
_soda_ is present. In both cases, it is necessary to confirm the results
by means of the spectroscope.
The above reactions are distinctive only in the absence of metals
precipitated by sulphuretted hydrogen, sulphide of ammonium or carbonate
of soda, and small portions of the solution should be tested with these
reagents.
In order to detect baryta, strontia and lime, the residue, insoluble in
alcohol is dissolved in dilute nitric acid, and an excess of carbonate
of ammonia added to the solution: the three bases, if present, are
precipitated as carbonates. The precipitate formed is separated from the
solution by filtration, dissolved on the filter in dilute hydrochloric
acid, and the solution then filtered and divided into two parts:
sulphuric acid is added to one, the fluid filtered from the precipitate
of sulphate of baryta formed, and the filtrate treated with ammonia and
oxalate of ammonia. If _lime_ be present,--although its sulphate is not
easily soluble--sufficient will be contained in the filtrate to give a
white precipitate of oxalate of lime.
The remaining portion of the solution is evaporated to dryness, and the
residue treated with absolute alcohol. Chloride of strontium goes into
solution, chloride of barium remaining undissolved. If upon evaporating
the alcoholic solution a residue is obtained which, when dissolved in
water, produces turbidity in a solution of sulphate of lime, _strontia_
is present.
The residue, insoluble in alcohol, is dissolved in water. If a
precipitate is produced by the addition of sulphuric acid or
hydrofluosilicic acid to the solution, _baryta_ is present. The latter
reaction distinguishes baryta from strontia, which is not precipitated
by hydrofluosilicic acid. Should the tests mentioned above fail to give
affirmative results, and poisoning by means of baryta and strontia be
nevertheless suspected, these compounds may possibly have remained in
the materials contained in the alimentary canal, in the state of
insoluble sulphates. To effect their detection under these circumstances
the organic substances must be decomposed by means of sulphuric acid.
The carbonaceous residue is calcined in a crucible at an elevated
temperature, and the remaining mass treated with water. In this way, a
solution of sulphides of barium and strontium is obtained, which is then
tested as directed above.
DETECTION OF CHLORINE, BROMINE, AND IODINE.
CHLORINE AND BLEACHING CHLORIDES.
The detection of chlorine is very difficult owing to the great tendency
it possesses to become converted into chlorides or hydrochloric acid,
and it is only when found in a free state that its discovery is of
importance.
In case the gas exists uncombined in the alimentary canal, its odor
will be perceptible, and, upon boiling the suspected materials with
water, vapors will be evolved which impart a blue color to paper
saturated with a mixture of iodide of potassium and starch paste. If the
addition of sulphuric acid is necessary in order to produce the above
reactions, there is reason to suspect the presence of "chloride of lime"
or "_Eau de Javelle_."[J]
[J] The so-called "chloride of lime" is probably either a mixture of
chloride and hypochlorite of calcium or an oxydichloride of the metal;
"_Eau de Javelle_" is the corresponding potassium compound.--_Trans._
BROMINE.
In case bromine exists in a free state at the time the autopsy is made,
its presence will be detected by the reddish color and unpleasant odor
it possesses. Its isolation is accomplished by treating the materials
with bisulphide of carbon which, upon dissolving the bromine, acquires a
red color. If potassa is then added to the solution, it combines with
the bromine and, upon evaporating the decanted fluid, calcining the
residue, and treating it with water, a solution of bromide of potassium
is obtained. Upon adding chlorine-water and ether to a portion of the
fluid, and shaking the mixture, the bromine is liberated and is
dissolved by the ether. The etherial solution of bromine, which
possesses a reddish-yellow color, does not mingle with, but floats upon
the surface of the colorless aqueous solution.
If nitrate of silver is added to another portion of the aqueous solution
of bromide of potassium, a precipitate of bromide of silver, soluble in
ammonia, is formed.
In case the bromine has been converted into a bromide, it is necessary
to boil the alimentary canal and the articles of food contained therein
with water. The fluid is next filtered and agitated with chlorine-water
and ether. The liberated bromine is dissolved by the ether, which
acquires a reddish-yellow color. Upon decanting the solution, and
treating it with potassa, bromide of potassium is formed, and can be
detected as directed above.
IODINE.
The detection of iodine is accomplished by a process almost identical
with the above. The isolation of the iodine having been effected, it
remains to be ascertained that it imparts a blue color to starch paste,
and a violet color to bisulphide of carbon.
DETECTION OF METALS.
Under this head we will indicate the systematic course of analysis to be
pursued, supposing a mixture of several metals including arsenic and
antimony, to be under examination.
The organic substances are first destroyed by means of chlorate of
potassa and hydrochloric acid. When this is accomplished, the excess of
chlorine is removed by boiling and the liquid filtered. The portion
remaining on the filter is preserved: it contains all the silver and a
large portion of the lead, if these metals are present. We will
designate the residue as A, the filtrate as B.
TREATMENT OF RESIDUE A.
The residue is calcined with a little carbonate of soda and cuttings of
pure Swedish filtering paper, the chlorides present being reduced to the
metallic state by this treatment. The residue is next taken up with
water acidulated with nitric acid, and the solution filtered. An
insoluble residue, that may remain, is washed with hot water until the
wash-water ceases to precipitate solution of nitrate of silver, and
dried. It is then dissolved in boiling nitric acid, the solution diluted
with water, and filtered.[K]
[K] If an insoluble residue remains by the treatment with nitric
acid, it may consist of _tin_. In this case, it is dissolved in _aqua
regia_, the metal precipitated by immersing a plate of zinc in the
solution and then re-dissolved in boiling hydrochloric acid. Upon
adding chloride of gold to the solution so obtained, a purple
precipitate is formed. Sulphuretted hydrogen produces a brown
precipitate, soluble in sulphide of ammonium, in presence of tin.
Sulphuric acid is added to the filtrate: if no precipitate forms, the
absence of _lead_, in the residue A, is indicated. If, on the contrary,
a precipitate is produced, it is collected upon a filter and washed. In
order to make sure that the precipitate consists of sulphate of lead, it
is treated with a solution of tartrate of ammonia: it should dissolve,
forming a solution in which sulphuretted hydrogen produces a black
precipitate.
The fluid which has failed to be precipitated by the addition of
sulphuric acid, or the filtrate separated from the precipitate formed,
can contain only silver. Upon adding hydrochloric acid, this metal is
thrown down as a caseous white precipitate, which is soluble in ammonia,
but insoluble in boiling nitric acid, and blackens upon protracted
exposure to light. The formation of a precipitate possessing these
properties, leaves no doubt as to the presence of _silver_.
_Remark._--In the operations described above, as well as in those
following, the difficulty in separating minute precipitates from the
filter is often experienced. When the precipitate is to be dissolved in
reagents that do not affect the paper, such as ammonia, tartrate of
ammonia, and dilute acids, it can be brought in solution directly on the
filter. In cases, however, where reagents which attack the paper are
employed, the precipitate should be separated. This is accomplished by
mixing a small quantity of pure silica, obtained by the decomposition of
fluoride of silicium by water, with the solution, before filtering. The
precipitate becomes intimately mixed with the silica, and can then be
readily removed from the paper. The presence of silica does not
interfere, it being insoluble in the reagents commonly made use of.
TREATMENT OF FILTRATE B.
A current of sulphuretted hydrogen is conducted for twelve hours through
the solution, which is kept at a temperature of 70°. by means of a
water-bath. The flask containing the liquid is then closed with a piece
of paper, and allowed to remain in a moderately warm place until the
odor of the gas is no longer perceptible. The solution is next filtered
with the precaution mentioned in the preceding remark, and the
precipitate (_a_) thoroughly washed. The water used in this operation is
united to the filtrate, and the fluid (_b_) examined as directed further
on.
TREATMENT OF PRECIPITATE _a_.
In order to free the precipitate from the organic substances possibly
present, at the same time avoiding a loss of any metal, it is dried,
moistened with nitric acid, and the mass heated on a water-bath. Some
Swedish filtering paper is next added, the mixture well impregnated with
sulphuric acid, and then maintained for several hours at a temperature
of about 170°. until a small portion (afterwards returned) gives a
colorless solution when treated with water. The residue is now heated
with a mixture of one part of hydrochloric acid and eight parts of
water, the liquid filtered, the matter remaining undissolved washed with
dilute hydrochloric acid, and the washings united with the filtrate.
The residue I. and the solution II. are separately examined as directed
below.
RESIDUE I.
This may contain lead, mercury, tin, bismuth and antimony. It is heated
for a considerable time with _aqua regia_, the solution filtered, and
the second residue, should one remain, washed with dilute hydrochloric
acid. If the second residue is fused with cyanide of potassium, the
compounds present are reduced to the metallic state. The liberated
metals are treated with nitric acid, which dissolves _lead_, but leaves
_tin_ as insoluble metastannic acid. The nitrate of lead is then
filtered from the metastannic acid, and both metals are identified as
described in the treatment of residue A.
The solution, obtained by the action of _aqua regia_ on residue I, is
treated with sulphuretted hydrogen. The tin and antimony are separated
from the lead, mercury and bismuth by treating the precipitate produced
with sulphide of ammonium, which dissolves only the sulphides of the
first two metals. The solution in sulphide of ammonium is afterwards
examined for these metals, as directed under the head of solution IV.,
the search for arsenic, however, being here omitted.
Upon treating the residue insoluble in sulphide of ammonium with nitric
acid, lead, copper and bismuth go into solution, mercury remaining
undissolved. The liquid is filtered, and the undissolved mercury
submitted to the special examination previously described.
Sulphuric acid is added to the solution and the precipitate of sulphate
of lead formed, separated, washed, and examined as directed while
treating of residue A.
Finally, the solution separated from the lead is tested for _bismuth_
and _copper_, as in examination of precipitate III.
SOLUTION II.
The solution is concentrated by heating on a water-bath, a small
quantity of carbonate of soda cautiously added to a portion, and notice
taken if a precipitate forms. The part taken is then acidulated with a
little hydrochloric acid, returned to the principal solution, and
sulphuretted hydrogen conducted through the fluid, as in the examination
of solution B. In case a precipitate fails to form, all metals are
absent; if, on the contrary, a precipitate (_c_) is produced, it is
examined as directed below.
EXAMINATION OF PRECIPITATE _c_.
If the solution merely became turbid, or the precipitate formed was of
a pure white color, it consists probably of sulphur. It is, however,
indispensable, even in this case, to collect the precipitate and examine
it for _arsenic_. Provided it is of a pure yellow color, it is treated
with ammonia. In case it is entirely dissolved by this treatment, and
the addition of carbonate of ammonia failed to produce a precipitate in
solution II., it is certain that arsenic, and no other metal, is
present. Under these circumstances, the ammoniacal solution is examined
as directed in the article on the detection of arsenic. If, on the other
hand, the precipitate is not yellow, or being yellow, is but imperfectly
soluble in ammonia, and a precipitate was formed by the addition of
carbonate of ammonia to solution II., it is necessary to likewise search
for tin, antimony, mercury, copper, bismuth and cadmium. In this case,
the precipitate is placed in a small flask, allowed to digest for
several hours with ammonia and sulphide of ammonium in a moderately warm
place, and the solution filtered.
The remaining residue (III.) is washed, labelled, and preserved for
subsequent examination; the _filtrate_ (IV.) is treated as directed
below.
TREATMENT OF SOLUTION IV.