hydrochloric acid, and an excess of ammonia added. Three cases are now
possible: (_a_) A precipitate, insoluble in an excess of the
precipitant, is immediately formed; (_b_) a precipitate is formed,
which, at first dissolves, but is subsequently deposited from the fluid;
(_c_) no precipitate is produced, or, in case one forms, it dissolves in
an excess of the precipitant and fails to separate out upon allowing the
fluid to stand.
_a. Ammonia produces a permanent precipitate._
A small quantity of an aqueous solution of carbonic acid is poured over
the alkaloid in the water-glass, and notice taken whether it dissolves
or not: in either case the mixture is evaporated on a water-bath to
dryness, in order to avoid a loss of substance.
CARBONIC ACID FAILS TO DISSOLVE THE ALKALOID.
After the evaporation is completed, ether is added to the watch-glass:
the alkaloid may, or may not, be dissolved. The ether is then evaporated
at the ordinary temperature of the air.
_Ether fails to dissolve the alkaloid._
It probably consists of _berberine_.
In this case, it will possess a yellow color, and its
hydrochlorate will give a reddish-brown precipitate
upon addition of sulphide of ammonia.
_Ether dissolves the alkaloid._--A small portion is
treated with nitric acid. If an intense green
coloration is produced, the remaining portion is
dissolved in ether, and an ethereal solution of oxalic
acid added. If the precipitate now formed does not
dissolve upon the addition of a little water, there is
reason to suppose the presence of _aricine_.
Provided the addition of nitric acid did not produce a
coloration, the mixture of the alkaloid and this acid
is treated with a small quantity of sulphuric acid: if
the fluid now acquires a red color, the substance
probably consists of _narcotine_.
Should both nitric and sulphuric acids fail to cause a
reaction, the alkaloid is dissolved in ether,
precipitated by an ethereal solution of oxalic acid,
and the precipitate treated with a little water. If it
dissolves, it probably consists of _papaverine_.
CARBONIC ACID DISSOLVES THE ALKALOID.
The substance is treated with ether, notice being taken if it dissolves,
which is evaporated at the ordinary temperature of the air so as to
prevent a loss of minute portions of the alkaloid.
_Ether dissolves the alkaloid._--If nitric acid gives
first a scarlet, then a yellow color, sulphuric acid a
yellow, changing to red and violet, and hydrochloric
acid a violet color, the alkaloid present is probably
_veratrine_.
If the above colorations are not produced, chlorine
water is added to another portion of the substance,
then ammonia; the formation of a green color, changing
to violet and turning red upon a renewed addition of
chlorine water, denotes the presence of _quinine_.
In case all of these tests give but negative results,
and the alkaloid is soluble in concentrated sulphuric
acid, a solution being formed which assumes a
reddish-violet tint when stirred with a glass rod
previously dipped in bromine water, the presence of
_delphine_.
is indicated.
_Ether fails to dissolve the alkaloid._--If the
substance is capable of being sublimed,[N] it consists
of _cinchonine_.
[N] Cinchonine, when sublimed, condenses in minute brilliant
needles.--_Trans._
_b. Ammonia produces a precipitate, which redissolves in an excess of
the precipitant, but separates out after the lapse of an hour._
The substance is treated with cold absolute alcohol
and its solubility in this menstruum noted. If it
readily dissolves, it probably consists of _brucine_.
The presence of this alkaloid is confirmed by applying
the following tests: (1) Nitric acid imparts a
blood-red color to the substance; (2) if treated with
sulphuric acid, it acquires a reddish tint which
subsequently changes to yellow and green; (3) chlorine
at first fails to cause a coloration, but after some
time a yellow color which afterwards changes to a red
is produced; (4) upon treating the substance with
bromine, it immediately assumes a violet tinge.
In case the alkaloid is only slightly soluble in
alcohol, there is reason to infer the presence of
_strychnine_.
The following confirmatory tests should be applied:
(1) If the substance is treated with a mixture of
sulphuric acid and an oxidizing body, such as
bichromate of potassa, binoxide of manganese, or
peroxide of lead it acquires a violet color, which
changes into red and finally passes into a clear
yellow; (2) the addition of bichloride of platinum
produces a precipitation of the hydrochlorate.
Should, however, the substance be only slightly soluble
in alcohol, and the above reactions fail to take place,
the presence of _solanine_.
is indicated. In presence of this alkaloid the following
reactions will occur: (1) Upon treating the substance
with concentrated sulphuric acid, it assumes a rose
tint, which changes after some time has elapsed first to
a deep violet, then to a brown color; (2) a solution of
a salt of the alkaloid reduces gold and silver salts;
(3) the addition of oxalic acid produces a precipitate
in the aqueous and even acid solution of its salts.
_c. Ammonia fails to produce a precipitate, or redissolves permanently
the one formed._
The solubility of the alkaloid in ether is ascertained. If it be
soluble, it may consist of aconitine, atropine or codeine; if insoluble,
of emetine or morphine.
_The alkaloid is soluble in ether._--If bichloride of
platinum fails to precipitate the hydrochlorate from a
neutral solution of the alkaloid, and sulphuric acid
causes it to assume a yellow color which subsequently
changes to a reddish-violet, it probably consists of
_aconitine_.
In case bichloride of platinum causes a precipitate
and sulphuric acid fails to produce the yellow
coloration referred to above, the presence of either
atropine or codeine is indicated. In order to decide
which of these bases is present, the substance is
dissolved in pure chloric acid and the solution allowed
to spontaneously evaporate. If the alkaloid is
deposited during this operation, it probably consists
of _atropine_.
If this is not the case, there is reason to infer the
presence of _codeine_.
_The alkaloid is insoluble in ether._--If it dissolves
in acetone it probably consists of _emetine_.
If acetone fails to dissolve it, the presence of
_morphine_.
is indicated.
The following confirmatory tests should be applied: (1)
Upon treating the substance with nitric acid, it
acquires a blood-red color; (2) the addition of a
solution of a persalt of iron produces an evanescent
blue coloration; (3) chloride of gold is colored blue,
when treated with the alkaloid; (4) the substance
reduces iodic acid: this reduction is detected by
adding to the acid a little starch-paste, which turns
blue upon the liberation of the iodine; (5)
permanganate of potassa, if heated with the substance,
is reduced and acquires a green color.
IDENTIFICATION OF DIGITALINE, PICROTOXINE AND COLCHICINE.
It has already been remarked that in exhausting the first acid solution
with ether--previous to the neutralization, according to Otto's
method--colchicine, a weak alkaloid, digitaline, an indefinite mixture,
picrotoxine (which appears to possess the properties of an acid), and
traces of atropine, pass into solution.
The ether is evaporated on a water-bath to dryness, the residuary mass
treated with slightly warmed water and the solution filtered from the
undissolved resinous matter. The aqueous solution is next rendered
feebly alkaline by addition of soda lye, and then well agitated with
ether, until this fluid ceases to leave a residue upon evaporation. The
ethereal solution is now decanted, and the water present removed by
means of chloride of calcium. If it is evaporated, a residue containing
the _colchicine_, _digitaline_ and traces of atropine (mixed possibly
with a minute quantity of picrotoxine, which is here left out of
consideration) is obtained.
_a._ The _alkaline solution_, from which the ether has been removed, is
acidulated with hydrochloric acid and again shaken with ether. The
_picrotoxine_ present is now dissolved, and upon dehydrating (by means
of fused chloride of sodium) and evaporating the ethereal solution can
be obtained in crystals. The crystals of picrotoxine are easily
recognized by their forming in feathery tufts as well as by their length
and silky brilliancy. Should crystals fail to form in a short time, it
is advisable to take up the residue, left by the evaporations of the
ether, with slightly warmed alcohol, and to allow the latter to
spontaneously evaporate on a watch-glass, or, if the quantity of
substance is exceedingly minute, on the slide of a microscope. After
determining the form of the crystals, it should be ascertained that they
possess an intense bitter taste and exhibit the other characteristic
properties of picrotoxine. The following reaction is distinctive: If the
crystals are dissolved in an aqueous solution of soda and a few drops of
"Fehling's solution"[O] added, a reddish precipitate of cuprous oxide is
formed.
[O] An alkaline solution of tartrate of copper, employed in the
examination of sugar, urine, and wine.--_Trans._
_b._ Provided picrotoxine has not been found, the _ethereal solution_
obtained by agitating the alkaline fluid with ether is to be examined
for colchicine and digitaline. To this end, the residue obtained upon
evaporating the solution to dryness is taken up with water, and the
filtered fluid tested as follows: 1. It is ascertained if a drop of the
solution possesses the bitter taste of digitaline. 2. Another drop is
treated with solution of tannin; if either alkaloid be present, a
precipitate is formed. 3. Two drops of the solution are next tested: one
with tincture of iodine, the other with chloride of gold. These reagents
precipitate colchicine, but do not affect solutions of digitaline or
picrotoxine. Unfortunately traces of atropine, possibly present, would
cause the same reaction; the test therefore fails to be conclusive. 4.
Several portions of the solution are evaporated on watch crystals.
Concentrated nitric acid is added to one portion: if colchicine be
present, an evanescent violet coloration is produced, which changes to a
light yellow upon addition of water, and to a pure yellow or
reddish-orange color, if the mixture is saturated with a slight excess
of caustic alkali. 5. Another portion of the residue is dissolved in a
few drops of concentrated sulphuric acid, and the solution stirred with
a glass rod moistened with bromine water: in presence of digitaline a
violet-red color is produced. This coloration is more distinct when a
small quantity of the alkaloid and an excess of sulphuric acid are
present. 6. If a large amount of substance is at hand, the residue can
be boiled with hydrochloric acid, and the green or brownish color and
characteristic odor of digitaline produced, in case this body be
present: this, however, is not a very delicate test. 7. Finally; it is
advisable when the presence of digitaline is suspected to ascertain its
physiological action. For this purpose, a minute quantity of the
substance is placed upon the heart of a frog: in presence of the
alkaloid, the pulsations are immediately retarded, or even arrested.
* * * * *
Although by means of the tests given above the existence of a special
alkaloid, or of one of the ill-defined substances just mentioned, may be
justly regarded as probable, its presence has not yet with certainty
been demonstrated. This is especially true in cases where the compound
possesses but few characteristic properties. When possible, the
suspected substance should be obtained in a crystaline form, and then
compared by aid of the microscope--if the small quantity present permits
of no other examination--with crystals of the pure alkaloid, prepared
under the same conditions.
In case 20 or even 10 centigrammes of substance are at hand, it is
best to convert the alkaloid into its hydrochlorate, and evaporate the
solution of this salt to dryness. The residue, after being weighed, is
dissolved in water, and a solution of sulphate of silver added. The
precipitate of chloride of silver formed is collected and carefully
weighed, in order to calculate the weight of the chlorine contained in
the hydrochlorate and consequently the molecular weight of the alkaloid.
The filtrate from the chloride of silver, which contains the alkaloid in
the state of sulphate, is treated with hydrochloric acid, to remove the
excess of silver present and the fluid then filtered. The filtrate is
next shaken with potassa and ether. Upon decanting and evaporating the
ethereal solution, a residue consisting of the alkaloid present is
obtained, which is then purified by crystallization from alcohol. An
elementary analysis of the alkaloid is now executed. _Certainty_ as to
the presence of an individual alkaloid is attainable only when the
execution of this confirmatory test is possible. The reactions
previously described can be performed with fifteen centigrammes of
substance, and this amount is sometimes contained in a cadaver. If but
one or two centigrammes are at hand, it is still possible to detect the
presence of an alkaloid; a conclusion, however, as to _which_ cannot be
arrived at, especially if the substance found is a liquid or an
amorphous body, and one that presents few distinctive properties.
III.
METHODS TO BE EMPLOYED, WHEN NO CLEW TO THE NATURE OF THE POISON PRESENT
CAN BE OBTAINED.
If poisoning has been caused by the administration of a mixture of
numerous substances and these greatly differ in their properties, it is
impossible to demonstrate in an incontestible manner the presence of
each individual poison. This contingency fortunately but seldom arises;
the criminal usually has recourse to one or two poisons, the detection
of which is possible. It must not be imagined, however, that the
presence of a poison in an organ can at once be detected with certainty
by the mere application of a few tests; because, in searching for a
substance which is absent, we may unwittingly destroy the one present,
or, at least, transform it into combinations which would not allow of a
definite conclusion as to its original condition.
In order to follow a systematic method in researches of this nature, it
is advisable to divide the materials under examination into three parts:
one portion is preserved, in order to ascertain its physiological
effects on animals, the chemical analysis having failed to give positive
results. The other portions are submitted to analysis, but with slightly
different objects in view; one is subjected to a series of tests which
are adapted, under all circumstances, to place the chemist on the track
of the poison present, and which, in some cases, may even give
conclusive and definite results. Should these tests furnish only
_indications_ of the nature of the poison, the remaining portion serves,
with the assistance of this information, to establish beyond doubt the
identity of the substance.
INDICATIVE TESTS.
Two cases may present themselves: the materials to be examined possess
either an alkaline (or neutral) or an acid reaction. As the methods to
be pursued in either of these cases differ somewhat, they will be
treated separately.
THE SUBSTANCE POSSESSES AN ACID REACTION.
The materials are mixed with water, placed in a retort provided with a
delivery-tube which dips in a solution of nitrate of silver, and heated
over a water-bath: if a _cyanide_ be present, hydrocyanic acid will be
disengaged, and a white precipitate of cyanide of silver formed: this is
examined as previously directed (_vide_ p. 50).
In case a precipitate is not produced by the above treatment, more
water is added to the retort, and the mixture boiled for about an hour,
care being taken to collect the evolved vapors in a well-cooled
receiver. The portion remaining in the retort is thrown on a filter and
the filtrate obtained united with the distillate. The residue remaining
on the filter is next washed with boiling absolute alcohol, the washings
being added to the aqueous solution. In this way, the suspected
substances are divided into soluble and insoluble portions, which are
examined separately, as directed below.
_a._ LIQUID PORTION.
If the addition of alcohol caused a precipitation of animal matters,
these are separated by filtering the solution. The filtrate is then
placed under a bell-jar over concentrated sulphuric acid until its
volume is considerably reduced. The solution may contain organic and
inorganic bases and acids. In order to detect all bodies that are
present, the following course is pursued:
(1). A current of sulphuretted hydrogen is conducted through the
solution: the precipitation of some metals, usually thrown down by this
gas, may fail to take place in this instance, owing to the presence of
organic substances; however, some metals are precipitated, even in
presence of organic compounds, and organic acids are but seldom present.
In case a precipitate is formed, it is mixed with pure silica, collected
on a filter, and treated with nitric acid. If the precipitate fails to
dissolve, it is treated with _aqua regia_. In either case, the solution
obtained is examined for metals by the ordinary methods.
(2). The solution in which sulphuretted hydrogen failed to produce a
precipitate, or the filtrate separated from the precipitate formed, is
divided into two parts: one portion is treated with ether and a solution
of potassa; the other with ether and a solution of soda. Both mixtures
are then well agitated, and notice taken if the ether dissolves any
thing: if so, the operation is repeated several times until all soluble
substances are removed. The ethereal solutions are next decanted and
united, and then submitted to the examination for alkaloids as directed
pp. 65-84.
(3). If--the above treatment giving either positive or negative
results--a precipitate insoluble in ether is formed by the addition of
potassa or soda, it is collected on a filter, washed, and dissolved in
an acid. The solution is then tested for mineral bases.
(4). In case no definite result has been obtained by the preceding
operations, one of the portions (for instance, the one to which potassa
was added) is tested for the acids possibly present in the state of
salts. The solution is divided into two parts (A and B) which are
examined separately:
PORTION A.--This is evaporated to dryness and the residue divided into
four parts which are then tested for hydrofluoric, nitric, oxalic, and
acetic and formic acids.
_a._ HYDROFLUORIC ACID.--A portion of the residue is heated in a
platinum crucible with sulphuric acid, and the crucible covered with the
convex face of a watch-crystal coated with wax in which lines have been
traced with a pointed piece of wood. If, after gently heating the
crucible for some time and removing the watch-crystal, the lines traced
in the wax are found to be etched in the glass, the substance under
examination contains a _fluoride_.
_b._ NITRIC ACID.--If this acid be present, and a second portion of the
residue is heated with sulphuric acid and copper, reddish-fumes are
evolved. Upon conducting the vapors into a solution of sulphate of iron
or narcotine, the reactions already mentioned in treating of nitric acid
take place.
_c._ OXALIC ACID.--The third portion of the residue is heated with
sulphuric acid, and the evolved gas carefully collected. It should then
be confirmed by an elementary analysis that the gas consists of equal
volumes of carbonic oxide and carbonic acid. This test is not
conclusive; it is also necessary to ascertain if the precipitate
produced by the addition of a baryta solution (_vide_: under portion
_B._) produces the same reaction, inasmuch as other organic bodies could
give rise to carbonic oxide and carbonic acid, and the danger of both
admitting the presence of oxalic acid, when it is absent, and omitting
its detection, in case it is present, would be incurred.
_d._ ACETIC AND FORMIC ACIDS.--The fourth portion of the residue is
distilled with dilute sulphuric acid. After determining that a small
portion, previously neutralized with a base, acquires a red color, upon
addition of a solution of a persalt of iron, the distillate is divided
into two parts. One portion is treated with bichloride of mercury: if
_formic acid_ be present, metallic mercury is formed, with evolution of
carbonic acid which produces turbidity in lime-water. The remaining
portion of the fluid is digested, in the cold, with an excess of
litharge: in presence of _acetic acid_, a soluble basic salt of lead,
possessing an alkaline reaction, is produced.
PORTION B.--The second portion of the solution is supersaturated with
nitric acid, and this neutralized by addition of a slight excess of
ammonia. The ammonia is then expelled by boiling the fluid, and a
solution of nitrate of baryta added. If a _precipitate_ forms, it is
collected and subsequently examined for sulphuric, phosphoric, oxalic
and boric acids as directed below. The _filtrate_ is preserved and
tested for hydrochloric, hydrobromic and hydriodic acids.
_a._ OXALIC ACID.--A portion of the precipitate produced by the addition
of nitrate of baryta is submitted to the test mentioned under the
treatment of portion _A_.
_b._ SULPHURIC ACID.--If an insoluble residue remains upon treating the
remainder of the precipitate with dilute hydrochloric acid, it consists
of sulphate of baryta and indicates the presence of _sulphuric acid_.
_c._ PHOSPHORIC ACID.--An excess of solution of alum and ammonia is
added to the portion of the precipitate dissolved in hydrochloric acid.
If phosphoric acid be present, insoluble phosphate of alumina is
precipitated. This is brought upon a filter: the _filtrate_ being
preserved and subsequently examined for boric acid. Upon boiling the
precipitate with solution of silicate of potassa, silicate of alumina is
thrown down, and phosphate of potassa remains in solution. Chloride of
ammonia is now added to the liquid--in order to eliminate the excess of
silica from the silicate--and the solution filtered. The _filtrate_ is
then tested for phosphates, by means of molybdate of ammonia (_vide_:
_detection of phosphoric acid_, p. 48).
_d._ BORIC ACID.--The filtrate from the precipitate of phosphate of
alumina is evaporated to dryness, the residue mixed with sulphuric acid
and alcohol, and the latter ignited. If the substance contains _boric
acid_, the alcohol will burn with a _green_ flame.
The _filtrate_, separated from the precipitate produced by the addition
of nitrate of baryta, may contain hydrochloric, hydrobromic and
hydriodic acids. In order to detect these compounds, some nitrate of
silver is added to the solution, and the precipitate that may form
carefully washed and decomposed by fusion with potassa. The mass is then
dissolved in water, and the solution submitted to the following tests:
_e._ HYDRIODIC ACID.--Some starch paste and nitric acid--containing
nitrous acid in solution--are added to a portion of the solution: in
presence of an _iodide_, the fluid immediately acquires a blue color.
_f._ HYDROBROMIC ACID.--In case iodine has not been detected, chlorine
water and ether are added to a second portion of the fluid, and the
mixture well agitated. If _bromine_ be present, the ether will assume a
_brown_ color. In case iodine is also contained in the fluid, and the
detection of bromine is desired, it is necessary to acidulate the
solution with hydrochloric acid, and then shake it with chloride of lime
and bisulphide of carbon. The bisulphide of carbon dissolves the iodine,
acquiring a _violet_ color, which disappears upon a renewed addition of
chloride of lime; whereas, in presence of bromine an _orange_ coloration
remains, even after the disappearance of the iodine reaction.