added, is evaporated to dryness, the residue obtained taken up with pure
fuming nitric acid, and the liquid again evaporated. The second residue
is next saturated with a solution of carbonate of soda. A mixture of 1
part of carbonate and 2 of nitrate of soda is then added, the mixture
evaporated to dryness, and the residual mass heated to fusion. The fused
mass, when cold, is treated with cold water, and any remaining residue
washed with a mixture of equal parts of alcohol and water. The filtered
fluids are now evaporated in order to remove the alcohol, sulphuric acid
is then added, and the mixture heated until white fumes of the acid
begin to evolve. In this way the complete expulsion of the nitric acid
present is rendered certain. When cold, the residue is treated with
water and the _solution_ introduced into Marsh's apparatus, or, in case
a quantitative estimation of the arsenic is desired, it is treated with
sulphuretted hydrogen and the weight of the precipitate formed
determined, as directed under the detection of arsenic.
Should a residue insoluble in water remain, it may contain tin,
antimony and traces of copper. Upon dissolving it in _aqua regia_ and
placing a sheet of pure zinc in the solution, these metals are thrown
down in the metallic state. The precipitate is collected, the zinc
present completely removed by treatment with _dilute_ hydrochloric acid,
and the residue boiled with concentrated hydrochloric acid which
dissolves the _tin_ present. The fluid is filtered and the _filtrate_
tested for this metal by adding solution of chloride of gold, which, in
its presence, produces a purple precipitate, and, by treating it with
sulphurated hydrogen, which forms a brown precipitate, soluble in
sulphide of ammonium.
If the _residue_, insoluble in concentrated hydrochloric acid, is
thoroughly washed and then treated with nitric acid, the copper present
goes in solution. The fluid is filtered, and ammonia added to the
filtrate: in presence of _copper_, the solution acquires a blue color,
and gives a reddish precipitate upon addition of ferrocyanide of
potassium.
_Antimony_, if present, remains by the treatment with nitric acid as an
insoluble intermediate oxide. This is dissolved in hydrochloric acid, in
which it is now soluble, and the solution introduced into Marsh's
apparatus.
TREATMENT OF PRECIPITATE III.
This precipitate may contain the sulphides of mercury, copper, cadmium
and bismuth. Upon treating it with nitric acid, all but the sulphide of
mercury are dissolved. In case no residue remains, the absence of
_mercury_ is indicated; if, on the other hand, a residue is left, it is
well washed, dissolved in _aqua regia_, and the solution examined,
either by means of Smithson's pile, or in the apparatus of Flandin and
Danger. (_Vide Detection of Mercury._)
Whether a residue remains or not, an excess of ammonia is next added to
the filtered solution in nitric acid: the formation of a permanent
precipitate denotes the presence of _bismuth_. In this case, the fluid
is filtered, and the alkaline filtrate further tested for copper and
cadmium. For this purpose, cyanide of potassium is added, and
sulphuretted hydrogen conducted through the filtrate: if _cadmium_ be
present, a yellow precipitate is produced, copper not being thrown down
in presence of an alkaline cyanide. The precipitate of sulphide of
cadmium is separated from the solution by filtration, and the filtrate
saturated with hydrochloric acid. _Copper_, if present, is now
precipitated as sulphide: its separation is completed by conducting
sulphuretted hydrogen through the fluid.
The precipitate is collected, washed, dissolved in nitric acid, and its
identity established as previously directed. If the metal be present in
sufficient quantity, it should be obtained in a metallic state upon a
plate of iron; it is then coherent, possesses its natural color, and can
conveniently be exhibited to the Jury.
TREATMENT OF SOLUTION _b_.
This solution may contain: cobalt, nickel, iron, manganese, chromium,
zinc and aluminium. Of these, only zinc and chromium are poisonous; the
search for these two metals is therefore all that is necessary in
criminal cases. The solution is treated with a slight excess of ammonia,
sulphide of ammonium added, and the fluid, after being allowed to stand
for several hours, filtered. The precipitate may consist of sulphide of
zinc and hydrated oxide of chromium, as well as of traces of sulphide of
iron and phosphate of lime. If the suspected materials contained a
_chromate_, this salt, in presence of hydrochloric acid and sulphuretted
hydrogen, would be converted into sesquichloride of chromium a compound
which is precipitated by sulphide of ammonium as a hydrated oxide.
The precipitate is washed with water, to which a little sulphide of
ammonium is added, then dried, and fused with four times its weight of a
mixture of equal parts of carbonate and nitrate of potassa. After the
mass has remained in a state of fusion for a quarter of an hour, it is
treated with boiling water, mixed with a little alcohol, in order to
decompose the manganate that would be present were manganese contained
in the materials under examination. The alcohol is then expelled by
boiling the fluid, and the solution filtered. The _filtrate_ may contain
phosphate of potassa, originating from the phosphate of lime present,
and _chromate of potassa_, resulting from the oxidation of the
sesquioxide of chromium. In presence of the latter compound, the
following reactions will occur in the solution: 1st., Upon acidulation
with acetic acid and addition of solution of acetate of lead, a yellow
precipitate, soluble in potassa, is formed; 2nd., if hydrochloric acid
is added and sulphuretted hydrogen conducted into the solution, the
latter acquires a green color, and, upon adding ammonia, a bluish-grey
precipitate of chromic hydrate is produced; 3rd., if nitrate of silver
is added to the solution, a brick-red precipitate is formed.
The _precipitate_ remaining on the filter, may consist of zinc, mixed
with the oxides of iron, nickel, cobalt, aluminium and manganese. It is
dissolved in boiling hydrochloric acid, acetate of soda added, and the
fluid boiled until no further precipitation occurs. The iron is now
completely separated. The solution is then filtered, the precipitate
washed, and an excess of potassa added to the _filtrate_; if the
solution contains cobalt, nickel or manganese--which is improbable--a
permanent precipitate is formed. This is separated from the fluid by
filtration: its further examination is, however, unnecessary, as the
metals of which it consists are not poisonous. The _filtrate_ may
contain aluminium and _zinc_. The latter metal is detected by
acidulating the filtrate with acetic acid, and adding a solution of
sulphuretted hydrogen: in presence of zinc a white precipitate of its
sulphide is formed.
In case organic substances are present, the precipitation of chromium by
sulphide of ammonium may possibly have been hindered, and the metal have
passed into the filtrate. When, therefore, chromium is not detected in
the precipitate, the filtrate should also be examined. For this purpose,
the fluid is evaporated to dryness, and the residue obtained fused with
a mixture of nitrate and carbonate of soda. The fused mass is then taken
up with water, the solution acidulated with acetic acid, and a solution
of acetate of lead added: if chromium be present, a yellow precipitate,
soluble in potassa, is produced.
DETECTION OF ALKALOIDS AND SOME ILL-DEFINED ORGANIC SUBSTANCES.[L]
A general method for effecting the detection of alkaloids was first
proposed by _Stas_. Since the publication of this method, modifications
to it have been recommended by _Otto_, and by _L. Uslar_ and _J.
Erdman_. Other processes have been suggested by _Rodgers_ and _Girwood_,
by _E. Prollius_, and by _Graham_ and _Hofman_. The latter will
doubtless become general in their application; but up to the present
time they have been employed exclusively in the detection of strychnine.
Dialysis has also been recently applied in the separation of alkaloids.
[L] Colchicine, picrotoxine and digitaline.
STAS'S METHOD.
This method is based upon the facts: (_a_), that the acid salts of the
alkaloids, especially those containing an excess of tartaric or oxalic
acids, are decomposed by caustic alkalies and by the bicarbonates of
soda and potassa; (_b_), that the alkaloids, when liberated in this
manner, are combined with a certain amount of water which determines
their solution in ether, although, in a desiccated state they may be
insoluble in this menstruum; (_c_), that they may be extracted from
their aqueous solutions by agitation with ether.
Stas's original method is as follows: The suspected substances, if
organs are contained, are cut into fine shreds, then mixed with absolute
alcohol, 0.5 to 2. grammes of tartaric or oxalic acid added and the
whole introduced into a flask and heated at a temperature of 60° to 75°.
When quite cold, the mixture is filtered, and the undissolved portion
remaining on the filter washed with absolute alcohol, the washings being
added to the filtrate. The alcoholic solution is evaporated, either by
placing it under a bell-jar connected with an air-pump, or by passing a
current of air, having a temperature not exceeding 35° over it, until
reduced to a quarter of its original volume: the complete expulsion of
the alcohol being then rendered certain. If insoluble matter separates
during this operation, the concentrated fluid is passed through a
moistened filter, the water used in washing the residue being united to
the filtrate which is then evaporated to dryness by aid of the air-pump
or by placing the fluid in a bell-jar over concentrated sulphuric acid.
When the evaporation is completed, the residue is treated with absolute
alcohol, the alcohol allowed to evaporate at the ordinary temperature of
the air, and the second residue dissolved in the smallest possible
amount of water. The fluid thus obtained is placed in a test-tube, and a
concentrated solution of bicarbonate of soda added so long as
effervescence takes place. Ether is then added, the mixture thoroughly
shaken, and after it has remained at rest for some time, a small portion
of the supernatant ether removed and evaporated on a watch-glass: the
residue obtained will consist of the alkaloid present. Two cases are now
possible: the alkaloid is a solid, or it is a liquid and is volatile.
The further treatment of the solution is modified according to these
circumstances.
_a._ THE ALKALOID IS LIQUID AND VOLATILE.
If, upon the evaporation of the ether, oily streaks were left on the
watch-glass, a volatile alkaloid is probably present.
In this case, a solution of caustic potassa is added to the test-tube,
the mixture shaken, the supernatant ether decanted[M] into a flask and
the remaining solution again washed with ether until the last portion
fails to leave a residue upon evaporation. The etherial fluids are then
united, and two cubic centimetres of water, acidulated with one-fifth of
its weight of sulphuric acid, added. This acid retains the alkaloid,
which is now in the state of a pure acid-sulphate soluble in water, the
animal matters present remaining dissolved in the ether. The ether, in
which some sulphate of conia may be contained--although the greater
portion of this compound would remain in the aqueous solution--is then
decanted. The remaining aqueous solution of the pure sulphate of the
alkaloid is placed in a test-tube, a solution of caustic potassa and
some ether added, and the mixture well shaken. The ether is next
decanted and allowed to spontaneously evaporate in a dry place at a very
low temperature, and the ammonia possibly present is then removed by
placing the vessel containing the residue over sulphuric acid. The
residue now obtained consists of the alkaloid present in a state of
purity, and can be directly identified by means of the reactions
described further on.
[M] The necessity of decanting etherial and other solutions is
advantageously obviated by the use of a pipette.--_Trans._
_b._ THE ALKALOID IS SOLID.
It sometimes occurs that ether fails to take up all of the alkaloid
present in the fluid treated with bicarbonate of soda. Under these
circumstances the fluid should be mixed with caustic potassa, the
mixture shaken, and the ether decanted; this operation being repeated
several times, until the entire amount of the alkaloid is removed; the
ethereal fluids are then united in a capsule, and allowed to
spontaneously evaporate. The result of the evaporation may be solid;
more frequently, however, a milky liquid remains which restores the blue
color to reddened litmus paper; if so, the presence of a vegetable
alkaloid is certain. In order to purify the residue, a few drops of
water, slightly acidulated with sulphuric acid, are added to the
capsule, and the latter turned, so as to bring the fluid in contact with
the substance at all points; in this manner a colorless and limpid fluid
is obtained, the fatty substances adhering to the dish. The liquid is
decanted into a second capsule, the remaining residue washed with a
little acidulated water, and the washings likewise added to the
principal solution. The fluid is now evaporated either _in vacuo_, or
over sulphuric acid, to about three-fourths of its original volume a
concentrated solution of neutral carbonate of potassa added, and the
mixture treated with absolute alcohol, which dissolves the liberated
alkaloid, and separates it from the sulphate of potassa formed and the
excess of carbonate of potassa. The alcoholic solution is decanted and
allowed to evaporate _in vacuo_ or in the air: the alkaloid now
crystallizes out in a state suitable for further examination.
MODIFICATIONS TO STAS'S METHOD, PROPOSED BY OTTO.
In Stas's method, the loss of morphine is possible, for, if ether is not
added immediately after the addition of carbonate of soda, this alkaloid
crystallizes and is then no longer soluble in that menstruum; and, if
the ethereal solution is not quickly decanted, the portion dissolved
will likewise separate out in small crystals. In both cases, morphine
will remain in the aqueous solution from which the other alkaloids have
been extracted by the ether. _M. Otto_ recommends the addition of
chloride of ammonium and a little soda-lye, in order to dissolve the
alkaloid. Upon allowing the solution so obtained to stand for some time
exposed to the air, crystals of morphine are deposited.
According to the same authority, it is advisable to omit the distinction
drawn by Stas between volatile and fixed alkaloids, and submit both to
the treatment recommended for those that are volatile.
Otto also recommends the agitation of the fluid containing the oxalates
or tartrates of the alkaloids with ether, previously to their separation
by means of bicarbonate of soda. By this treatment the elimination of
the coloring matter present--as well as of _colchicine_, _digitaline_,
_picrotoxine_, traces of _atropine_, and various impurities--is
accomplished. As soon as the ether ceases to become colored and to leave
a residue upon evaporation, alkali is added, and the operation concluded
as usual. In this way the alkaloid is obtained, almost directly, in a
pure condition. This last modification appears to us to be a very happy
one, inasmuch as it greatly facilitates the purification of the alkaloid
present.
MODIFICATIONS TO STAS'S METHOD, PROPOSED BY USLAR AND ERDMAN.
1st. The materials to be examined are brought to the consistence of a
thin paste, and digested for about two hours with water, to which some
hydrochloric acid has been added, at a temperature of 60° to 80°. The
mixture is then filtered through a moistened linen cloth, and the
residue washed with warm acidulated water; the washings being added to
the solution.
2nd. Some pure quartz sand--or, preferably, silica prepared by the
decomposition of fluoride of silicium--is added to the filtrate, the
fluid supersaturated with ammonia, and evaporated to dryness over a
water-bath: the addition of silica renders the residue friable.
3rd. The residue is boiled repeatedly with amylic alcohol, which
extracts all the alkaloid present as well as the fatty and coloring
matters, and the extracts filtered through filter paper that has been
moistened with amylic alcohol.
4th. The filtered fluid is thoroughly agitated with ten or twelve times
its volume of almost boiling water acidulated with hydrochloric acid:
the hydrochlorate of the alkaloid present goes into the aqueous
solution, the fatty and coloring substances remaining dissolved in the
oily supernatant layer. The latter is separated by means of a pipette,
and the acid aqueous solution shaken with fresh quantities of amylic
alcohol until completely decolorized.
5th. The aqueous solution is then concentrated, ammonia added, and the
mixture well shaken with warm amylic alcohol, in which the alkaloid
dissolves. As soon as the solution forms a supernatant layer upon the
surface of the fluid, it is drawn off with a pipette and evaporated on a
water-bath. In this manner, the alkaloid is usually obtained in a
sufficient state of purity to admit of its immediate identification; if,
however, a small portion turns brown when treated with concentrated
sulphuric acid, the process of purification must be repeated. Under
these circumstances it is re-dissolved in dilute hydrochloric acid, the
solution repeatedly shaken with amylic alcohol, in order to extract the
impurities present, and the alkaloid then extracted with ammonia and
amylic alcohol, as previously directed.
The method of _von Uslar_ and _Erdman_ differs from that of Stas merely
in the substitution of amylic alcohol for ether, and of hydrochloric
acid for oxalic or tartaric acid. It offers no advantages over Stas's
method if the alkaloids present are soluble in ether but is even less
advantageous in this case, inasmuch as its execution requires a longer
time. In cases where the detection of morphine, or an unknown alkaloid,
is desired, the use of amylic alcohol instead of ether is, it is true,
preferable; still, with the exercise of care, ether can also be
employed, and, as this process greatly facilitates examinations when no
clew to the poison present exists and all alkaloids may possibly be
absent, we prefer it to the one just described.
RODGERS AND GIRDWOOD'S METHOD.
This method--which as yet has only been employed in the detection of
strychnine--is based upon the solubility of this alkaloid in chloroform.
The substances under examination are digested with dilute hydrochloric
acid, and the mixture filtered. The filtrate is then evaporated to
dryness on the water-bath, the residue taken up with pure alcohol, the
alcoholic solution evaporated, the second residue treated with water,
and the solution so obtained filtered. The filtrate is next
supersaturated with ammonia, and well shaken with chloroform, which,
upon being separated by means of a pipette and evaporated, leaves the
alkaloid in an impure state. Concentrated sulphuric acid is then poured
upon the alkaloid: the latter is not affected by this treatment, whereas
the foreign organic substances present are carbonized. After the lapse
of several hours, the mixture is treated with water, the fluid filtered,
and the strychnine extracted from the filtrate by means of ammonia and
chloroform, as already described. The operation is repeated until the
residue obtained by evaporating the chloroform is no longer affected by
the treatment with sulphuric acid.
PROLLIUS'S METHOD.
The suspected substances are boiled with aqueous alcohol, mixed with
tartaric acid, and evaporated at a gentle heat. The remaining aqueous
solution is then passed through a moistened filter, ammonia added to the
filtrate, and the mixture shaken with chloroform. The chloroform is
separated, the last trace of the original solution removed by washing
with water, three parts of alcohol added, and the fluid evaporated. If
strychnine be present, it will now separate out in crystals. This method
is applicable only in presence of a considerable quantity of strychnine,
and is less serviceable than the one preceding.
GRAHAM AND HOFMAN'S METHOD.
This method, which is applied to the detection of strychnine in beer, is
founded upon the fact that an aqueous solution of a strychnine salt
yields the alkaloid to animal charcoal, from which it can be
subsequently extracted by boiling with alcohol. The beer to be examined
is shaken with 30 grammes of animal charcoal, and the mixture then
allowed to stand twenty-four hours, with occasional shaking. The
solution is next filtered, the animal charcoal washed with water, and
boiled for half-an-hour with four times its weight of 90 per cent.
alcohol. The apparatus represented in Fig. 12 is employed, in order to
avoid a loss of substance in this operation.
[Illustration: Fig. 12.]
The alcohol is filtered hot, evaporated, and the residue obtained
treated with a small quantity of solution of potassa, and then agitated
with ether. Upon spontaneous evaporation, the ethereal solution leaves
the strychnine present in a comparatively pure state.
_Macadam_ proposes to use this process for the detection of strychnine
in animal bodies. For this purpose, the suspected materials are heated
with a solution of oxalic acid, as in Stas's method, and the strychnine
detected in the filtered solution in the manner just described. This
method is scarcely to be recommended: the use of animal charcoal is
doubtless serviceable in the examination of beer, as it effects the
separation of a small amount of strychnine from a large quantity of
fluid, but its application to other researches is much less to be
advised.
APPLICATION OF DIALYSIS IN THE DETECTION OF ALKALOIDS.
In order to apply the dialytic method to the separation of alkaloids,
the suspected substances are heated with hydrochloric acid, and the
solution introduced into the dialyzer. The hydrochlorates of the
alkaloids, being crystalline bodies, transverse the membrane, and are
contained, for the greater part, after twenty-four hours, in the outer
solution. The fluid is then concentrated, and the alkaloids either
directly precipitated, or purified by one of the preceding methods.
IDENTIFICATION OF THE ALKALOID.
The alkaloid having been isolated by one of the preceding methods, it
remains to establish its identity. Owing to the small number of
reactions characteristic of organic compounds, this is a matter of
considerable difficulty. There are two cases possible: the alkaloid may
either be volatile or fixed.
THE ALKALOID IS VOLATILE.
In this case it may consist of nicotine, conine or aniline: less known
alkaloids (piccoline, etc.) may also be present. We will confine
ourselves to the consideration of the three first mentioned.
The alkaloid is divided into several portions which are placed on
watch-glasses and submitted to the following tests:
_a._ A drop is treated with nitric acid: this may, or
may not, impart a red tint to the alkaloid; if it
does, another drop is treated with dry hydrochloric
acid gas: if it assumes a deep violet color, it
probably consists of _conine_.
_b._ In case a red color was not produced by the
addition of nitric acid, another drop is treated with
chloride of lime. If it acquires a violet tint, and
two other drops, when heated, one with arsenic acid,
the other with nitrate of mercury, become red, the
body present consists of _aniline_.
or an homologous base.
_c._ Should the above tests fail to give positive
results, and the substance, when treated with
chlorine, assumes a blood-red color, and with
hydrochloric acid does not change in the cold but
turns to a deep violet color upon boiling, it probably
consists of _nicotine_.
THE ALKALOID IS FIXED.