LEGAL CHEMISTRY.
A GUIDE
TO THE
DETECTION OF POISONS,
EXAMINATION OF TEA, STAINS, ETC.,
AS APPLIED TO
CHEMICAL JURISPRUDENCE.
TRANSLATED WITH ADDITIONS FROM THE FRENCH OF
A. NAQUET,
_Professor to the Faculty of Medicine of Paris_.
BY
J. P. BATTERSHALL, Nat. Sc. D., F.C.S.
_SECOND EDITION, REVISED, WITH ADDITIONS._
NEW YORK:
D. VAN NOSTRAND, PUBLISHER,
23 MURRAY STREET AND 27 WARREN STREET.
1884.
COPYRIGHT.
D. VAN NOSTRAND.
1876.
Transcriber's Note:
Text originally marked up as bold is surrounded by *, text in italics by
_. Obvious printer errors have been corrected. A list of all other
changes can be found at the end of the document. In the Appendix of the
book, only the most obvious errors of punctuation were remedied.
PREFACE.
The importance of exact chemical analysis in a great variety of cases
which come before the courts is now fully recognized, and the
translation of this excellent little book on Legal Chemistry, by one of
the most distinguished French Chemists, will be appreciated by a large
class of American readers who are not able to consult the original.
While it is to be regretted that the author has not presented a much
more complete work, there is an advantage in the compact form of this
treatise which compensates, in some degree, for its brevity.
The translator has greatly increased the value of the book by a few
additions and his copious index, and especially by the lists of works
and memoirs which he has appended; and while he could have further
increased its value by additions from other authors, we recognize the
weight of the considerations which induced him to present it in the form
given to it by the author. Some chapters will have very little value in
this country at this day, but the translator could not, with propriety,
omit anything contained in the original.
C. F. CHANDLER.
PREFACE TO THE SECOND EDITION.
The principal change to note in this edition of the LEGAL CHEMISTRY is
the addition of a chapter on Tea and its Adulteration. The general
interest at present evinced concerning this species of sophistication
appeared to call for a simple and concise method of examination which
would include the requisite tests without entering upon an exhaustive
treatment of the subject. The translator's practical experience in the
testing of tea at the United States Laboratory of this city has enabled
him to make a few suggestions in this regard which, he trusts, may be of
use to those interested in food-analysis. Numerous additions have also
been made to the bibliographical appendix.
J. P. B.
CONTENTS.
PAGE
INTRODUCTION 5
METHODS OF DESTRUCTION OF THE ORGANIC SUBSTANCES
By means of Nitric Acid 8
" " Sulphuric Acid 9
" " Nitrate of Potassa 10
" " Potassa and Nitrate of Lime 12
" " Potassa and Nitric Acid 12
" " Chlorate of Potassa 13
" " Chlorine 13
" " _Aqua Regia_ 14
Dialysis 15
DETECTION OF POISONS, THE PRESENCE OF WHICH IS SUSPECTED.
Detection of Arsenic 17
_Method used prior to Marsh's test_ 17
_Marsh's test_ 21
_Raspail's test_ 29
_Reinsch's test_ 30
Detection of Antimony 30
_Flandin and Danger's apparatus_ 32
_Naquet's apparatus_ 34
Detection of Mercury 36
_Smithson's pile_ 36
_Flandin and Danger's apparatus_ 37
Detection of Phosphorus 39
_Orfila's method_ 39
_Mistcherlich's method_ 40
_Dusart's method, as modified by Blondlot_ 40
_Fresenius and Neubauer's method_ 42
_Detection of Phosphorus by means of bisulphide of carbon_ 43
_Detection of Phosphorous Acid_ 45
_Estimation of Phosphorus_ 45
Detection of Acids 46
_Hydrochloric Acid_ 46
_Nitric_ " 47
_Sulphuric Acid_ 47
_Phosphoric_ " 48
_Oxalic_ " 49
_Acetic_ " 49
_Hydrocyanic_ " 50
Detection of alkalies and alkaline earths 52
Detection of chlorine, bromine and iodine 54
_Chlorine and Bleaching Chlorides_ 54
_Bromine_ 55
_Iodine_ 56
Detection of Metals 56
Detection of alkaloids and some ill-defined organic substances 65
_Stas's method_ 65
" " _as modified by Otto_ 69
" " " " _Uslar and Erdman_ 70
_Rodgers and Girdwood's method_ 71
_Prollius's method_ 72
_Graham and Hofman's method_ 73
_Application of Dialysis in the detection of Alkaloids_ 74
_Identification of the Alkaloid_ 74
_Identification of Digitaline, Picrotoxine and Colchicine_ 80
METHOD TO BE EMPLOYED WHEN NO CLEW TO THE NATURE OF THE
POISON PRESENT CAN BE OBTAINED 85
Indicative tests 86
Determinative tests 94
MISCELLANEOUS EXAMINATIONS 96
Determination of the nature and color of the hair and beard 96
_Determination of the color of the hair and beard_ 96
_Determination of the nature of the hair_ 99
Examination of Fire-arms 100
_The gun is provided with a flint-lock and was charged with
ordinary powder_ 100
_The gun is not provided with a flint-lock_ 103
Detection of human remains in the ashes of a fire-place 104
Examination of writings 105
Examination of writings, in cases where a sympathetic ink has
been used 110
Falsification of coins and alloys 112
Examination of alimentary and pharmaceutical substances 114
_Flour and Bread_ 114
_Fixed Oils_ 128
_a Olive Oil intended for table use_ 128
_b Olive Oil intended for manufacturing purposes_ 130
_c Hempseed Oil_ 130
_Tea_ 130
_Milk_ 137
_Wine_ 142
_Vinegar_ 147
_Sulphate of Quinine_ 148
Examination of blood stains 150
Examination of spermatic stains 158
APPENDIX 163
Books of Toxicology, etc. 163
Memoirs on Toxicology, etc. 168
INDEX 187
LEGAL CHEMISTRY.
The term Legal Chemistry is applied to that branch of the science which
has for its office the solution of problems proposed in the interest of
Justice. These most frequently relate to cases of poisoning. When the
subject of the symptoms or anatomical lesions produced by the reception
of a poison is under consideration, the services of a medical expert are
resorted to; but when the presence or absence of a poison in the organs
of a body, in the _egesta_ of an invalid or elsewhere is to be
demonstrated, recourse is had to the legal chemist. Investigations of
this character require great practice in manipulation, and, however well
the methods of analysis may be described in the works on the subject,
there would be great danger of committing errors were the examination
executed by an inexperienced person. The detection of poisons, although
perhaps the most important, is not the only subject that may come within
the province of the legal chemist; indeed, it would be somewhat
difficult to define, _a priori_, the multitude of questions that might
arise. In addition to cases of supposed poisoning, the following
researches are most often required:
1. The examination of fire-arms.
2. The analysis of ashes, in cases where the destruction of a human
body is suspected.
3. The detection of alteration of writings, and of falsification of
coins and precious alloys.
4. The analysis of alimentary substances.
5. The examination of stains produced by blood and by the spermatic
fluid.
Each of these researches justly demands a more extended consideration
than the limits of this work would permit. The several subjects will be
treated as briefly as possible, and at the same time, so as to convey an
exact idea of the methods employed, leaving to the expert the selection
of the particular one adapted to the case under investigation. We will
first mention the methods used in the search for toxical substances. The
poisons employed for criminal purposes are sometimes met with in a free
state, either in the stomach or intestines of the deceased person, or in
the bottles discovered in the room of the criminal or the victim. Under
these circumstances, it is only necessary to establish their identity by
means of their chemical properties, as directed in the general treatises
on chemistry, or by their botanical, or zoological character, in case a
vegetable or animal poison, such as cantharides, has been administered.
Examinations of this class are extremely simple, the analysis of the
substances found, confined to a few characteristic reactions, being a
matter of no great difficulty. We will not here dwell longer upon this
subject, inasmuch as the analytical methods used are identical with
those employed in more complicated cases, with the sole difference that,
instead of performing minute and laborious operations in order to
extract the poisons from the organs in which they are contained, with a
view of their subsequent identification, we proceed at once to establish
their identity. The directions given in regard to complicated
investigations apply, therefore, equally well to cases of a more simple
nature. The detection of a poison mixed with the organic substances
encountered in the stomach, or absorbed by, and intimately united with
the tissues of the various organs is more difficult. If, however, other
information than chemical can be obtained, indicating the poison
supposed to be present, and the presence or absence of this one poison
is the only thing to be determined, positive methods exist which admit
of a speedy solution of the question. When, on the other hand, the
chemical expert has not the advantage of extraneous information, but is
simply asked,--whether the case be one of poisoning?--nothing being
specified as to the nature of the poison used, the difficulty of his
task is greatly increased. Up to the present time, the works on
Toxicology have, it is true, given excellent special tests for the
detection of particular poisons; but none have contained a reliable
general method, which the chemical expert could use with the certainty
of omitting nothing. Impressed with this need, we proposed, in 1859, in
an inaugural dissertation then presented to the Faculty of Medicine, a
general method, which, after some slight modifications, is now
reproduced. The special methods which allow of the detection of various
individual poisons will, however, first be indicated. In cases where the
poison is mixed with organic matter, the latter must be removed as the
first step in the investigation, as otherwise the reactions
characteristic of the poison searched for would be obscured. When the
poison itself is an organic substance, this separation is effected by
processes modified according to the circumstances. If the detection or
isolation of a metallic poison is to be accomplished, the most simple
method consists in the destruction of the organic substances. The
various methods for effecting this decomposition will now be described.
I.
METHODS OF DESTRUCTION OF THE ORGANIC SUBSTANCES.
BY MEANS OF NITRIC ACID.
In order to destroy the organic matters by this process, a quantity of
nitric acid equal to one and a half times the weight of the substances
taken is heated in a porcelain evaporating dish, the amount of acid
being increased to four or six times that of the organic substances if
these comprise the brains or liver. As soon as the acid becomes warm,
the suspected organs, which have previously been cut into pieces, are
added in successive portions: the organs become rapidly disintegrated,
brownish-red vapors being evolved. When all is brought into solution,
the evaporation is completed and the carbonaceous residue obtained
separated from the dish and treated either with water, or with water
acidulated with nitric acid, according to the nature of the poison
supposed to be present.
Several objections to this method exist, the most serious of which is
based upon the fact that the carbonaceous residue, containing, as it
may, nitric acid, readily takes fire and may therefore be consumed, or
projected from the vessel. This objection is a grave one, and is not
always entirely removed by the continual stirring of the materials.
According to _M. Filhol_, the addition of 10 to 15 drops of sulphuric
acid to the nitric acid taken obviates the difficulty; not having
personally tested the question we cannot pronounce upon it. If it be the
case, this process is an advantageous one, as it is not limited in its
application, but can be used in the separation of all mineral poisons.
BY MEANS OF SULPHURIC ACID.
The organic matter to be decomposed is heated with about one-fifth of
its weight of concentrated sulphuric acid, the complete solution of the
materials being thus accomplished. The excess of acid is next removed by
heating until a spongy carbonaceous mass remains. The further treatment
of this residue depends upon the nature of the poison supposed to be
present. If the sulphate of the suspected poison is a soluble and stable
compound, the residue is directly treated with water; if, on the
contrary, there is reason to think that the sulphate has suffered
decomposition, the mass is taken up with dilute nitric acid; if,
finally, the presence of arsenic is suspected, the residue is moistened
with nitric acid, in order to convert this body into arsenic acid. The
acid is afterwards removed by evaporation, the well pulverized residue
boiled with distilled water, and the solution then filtered.
This method, when applied in the detection of arsenic, is objectionable
in that the carbonaceous residue, in contact with sulphuric acid, almost
invariably contains sulphurous acid, detected by means of permanganate
of potassa. This acid, being reduced in the presence of hydrogen, would
cause the formation of insoluble sulphide of arsenic, and in this way
prevent the detection of small amounts of arsenic by the use of Marsh's
apparatus. _M. Gaultier de Claubry_, indeed, states that he has not been
able to detect the presence of sulphurous acid in the carbonaceous
residue; but one affirmative result would, in this case, outweigh twenty
negative experiments. A further objection to this process consists in
the fact that the materials to be destroyed almost always contain
chlorides, which, in presence of sulphuric acid and an arsenical
compound, might determine the formation of chloride of arsenic, a
volatile body, and therefore one easily lost. This difficulty is
doubtless of a less serious nature than the preceding, as the operation
can be performed in a closed vessel provided with a receiver which
admits of the condensation of the evolved vapors; but even then the
process would be prolonged. The above method is still again
objectionable on account of its too limited application, it being
serviceable almost exclusively in cases where the poisoning has been
caused by arsenic, for, if applied in other instances, a subsequent
treatment would be necessary in order to redissolve the metal separated
from its decomposed sulphate.
BY MEANS OF NITRATE OF POTASSA.
This method was formerly executed as follows: Nitrate of potassa was
fused in a crucible, and the substances to be destroyed added in small
portions to the fused mass. The organic matter soon acquired a pure
white color; owing, however, to the imperfect admixture of the organic
matter with the salt used for its decomposition, it was necessary to
take a large excess of the latter.
The following process, suggested by _M. Orfila_, remedies this
inconvenience: The organs are placed in an evaporating dish, together
with one tenth of their weight of caustic potassa, and a quantity of
water varying with the weight of the substances taken. An amount of
nitrate of potassa equal to twice the weight of the organic matter is
next added, and the mixture evaporated to dryness. The residue is then
thrown by fragments into a Hessian crucible heated to redness, the
portions first taken being allowed to become perfectly white before more
is added.
Whichever process has been employed, the fused mass is decanted into a
porcelain crucible, which has previously been heated in order to avoid
danger of breakage. The portion remaining in the vessel is taken up by
boiling with a small quantity of distilled water, and the solution so
obtained likewise added to the crucible. The mass is then heated with
sulphuric acid until all nitrous fumes are expelled, as these could give
rise to an explosion, when, in the search for arsenic, the substance is
introduced into Marsh's apparatus. As soon as the nitric acid is
completely expelled, the liquid is allowed to cool; the greater portion
of the sulphate of potassa formed now separating out in crystals. The
fluid is next filtered and the crystalline salt remaining on the filter,
washed, at first with a little distilled water, then with absolute
alcohol, which is subsequently removed from the filtrate by boiling.
This method is scarcely applicable otherwise than in the detection of
arsenic, as in other instances the presence of a large amount of
sulphate of potassa would be liable to affect the nicety of the
reactions afterwards used. Its application, even in the search for
arsenic, is not to be strongly recommended; on the contrary, the
separation of the potassa salt by filtration is indispensable, as
otherwise a double salt of zinc and potassium, which might be formed,
being deposited upon the zinc used in Marsh's apparatus, would prevent
the disengagement of hydrogen, and every chemist is too well aware of
the difficulty of thoroughly washing a precipitate, not to fear the
possible loss of arsenic by this operation.
BY MEANS OF POTASSA AND NITRATE OF LIME.
In this method the organic materials are heated with water and 10 to 15
per cent. of caustic potassa. As soon as disintegration is completed,
nitrate of lime is added, and the mixture evaporated to dryness. A
glowing coal is then placed upon the carbonaceous residue obtained: the
mass, undergoing combustion, leaves a perfectly white residue. This
residue dissolves in hydrochloric acid to a clear fluid which is then
examined for poisons.
The above process possesses the undeniable advantage of completely
destroying the organic substances, at the same time avoiding the
introduction of sulphate of potassa, the presence of which impairs the
usefulness of the preceding method; but it necessitates the presence of
numerous foreign bodies in the substance to be analysed, and this should
be avoided. The _absolute purity_ of reagents is not always to be
attained, and the results of an analysis are the more certain, in
proportion as they are less numerous and more easily purified.
BY MEANS OF POTASSA AND NITRIC ACID.
It has been proposed, instead of using nitrate of lime, to dissolve the
organic matter in potassa and then saturate the fluid with nitric acid.
This method is evidently more complicated than the simple treatment with
nitrate of potassa, and possesses, moreover, no advantages over the
latter process.
BY MEANS OF CHLORATE OF POTASSA.
The organic materials are treated with an equal weight of pure
hydrochloric acid, and water added, so as to form a clear pulp. This
being accomplished, two grammes of chlorate of potassa are added to the
mixture at intervals of about five minutes. The fluid is next filtered,
and the insoluble residue remaining on the filter washed until the
wash-water ceases to exhibit an acid reaction. The filtrate is then
evaporated, an aqueous solution of sulphurous acid added, until the odor
of this reagent remains distinctly perceptible, and the excess of the
acid removed by boiling the solution for about an hour. The fluid is now
adapted to further examination for arsenic, or other metallic poisons.
This method is one of the best in use, both chlorate of potassa and
hydrochloric acid being reagents easily procured in a state of great
purity; their use, however, is liable to the objection that they convert
silver and lead into insoluble chlorides.
BY MEANS OF CHLORINE.
_M. Jacquelain_ suggests, in the search for arsenic, the decomposition
of the organic matters by means of a current of chlorine, and recommends
the following process: The organic substances are bruised in a mortar
and then macerated with water. The fluid so obtained, in which the
organic matter is held suspended, is next placed in a flask into which a
current of chlorine is passed until all the organic matter is deposited
in colorless flakes on the bottom of the vessel. The flask is then well
closed and allowed to stand for 24 hours, when the odor of the gas
should still be perceptible. The fluid is now filtered, the filtrate
concentrated by heating in a vessel which permits of the preservation of
the volatile chloride of arsenic possibly present, and then examined for
poisons.
This process fails to possess the degree of generality desirable, and
presents the disadvantage of requiring considerable time for its
execution.
BY MEANS OF AQUA REGIA.
This method is exceedingly simple: _Aqua regia_ (a mixture of two parts
of hydrochloric and one part of nitric acids) is placed in a tubular
retort provided with a receiver, and the organic materials, which have
previously been cut into small pieces, added; the reaction commences
immediately; if it is not sufficiently active, it is accelerated by a
gentle heat: lively effervescence now occurs, and the destruction of all
non-oleaginous substances is soon accomplished. The latter substances
alone are not immediately decomposed by _aqua regia_, which attacks them
only after prolonged action. As soon as the operation is concluded, the
apparatus is removed from the fire and taken apart. The fluid condensed
in the receiver is added to that remaining in the retort, and the whole
thoroughly cooled in an open dish. The fatty matters now form a solid
crust upon the surface of the fluid, which is removed and washed with
distilled water, and, the washings being added to the rest of the
solution, the latter is directly examined for metallic poisons. It is
recommended by _Gaultier de Claubry_, in cases where the detection of
arsenic is desired, to saturate and afterwards boil the suspected fluid
with sulphuric acid, in order to remove the nitric and hydrochloric
acids present.
DIALYSIS.
The application of the dialytic method was first proposed by _Graham_.
By its use we are enabled to distinguish between two large classes of
bodies, viz., _colloids_ and _crystalloids_. Albumen, gelatine, and
analogous substances are typical of colloid bodies; crystalloid
substances, on the other hand, are those that are capable of
crystallization, either directly or in their compounds, or, in case they
are fluids, would possess this property when brought to the solid state.
Graham discovered that when an aqueous solution containing a mixture of
colloid and crystalloid substances is placed in a vessel having for its
bottom a piece of parchment or animal membrane, and this is immersed in
a larger vessel filled with water, all of the crystalloids contained in
the first vessel transverse the porous membrane and are to be found in
the larger vessel, the colloid bodies being retained above the membrane.
The organic matter to be eliminated in toxicological researches being
colloids, and the poisons usually employed being crystalloids, the value
of dialysis as a method of separation is evident. The process is
executed as follows:
[Illustration: Fig. 1.]
A wooden,--or better, a gutta-percha--cylinder (Fig. 1), 5 cubic
centimetres in height and from 20 to 25 c. c. in diameter, is employed.
A piece of moistened parchment is securely attached to one of the
openings of the cylinder, which, upon drying, shrinks and completely
closes the aperture. If its continuity becomes impaired, the pores of
the membrane should be covered with the white of an egg which is
subsequently coagulated by the application of heat. The organs
previously cut into small pieces, or the materials found in the
alimentary canal, etc., after having been allowed to digest for 24 hours
in water at 32°[A]--or, in dilute acids, if the presence of an alkaloid
is suspected,--are then placed in the upper vessel, which is termed the
dialyser. The whole should form a layer not over 2 cubic centimetres in
height. The dialyser is next placed in the larger vessel filled with
distilled water. In about 24 hours three-quarters of the crystalloid
substances present will have passed into the lower vessel. The solution
is then evaporated over a water-bath, and submitted to analysis. The
portion remaining in the dialyser is decomposed by one of the methods
previously described, in order to effect the detection of any poisonous
substances possibly present. Instead of the above apparatus, the one
represented in Fig. 2 can be employed. The fluid under examination is
placed in a bell-shaped jar, open at the top and closed below with a
piece of parchment, which is then suspended in the centre of a larger
vessel containing water. In other respects the operation is performed in
the same manner as with the apparatus represented in Fig. 1.
[Illustration: Fig. 2.]
[A] The degrees of temperature given in the text refer to the
centigrade Thermometer; their equivalents on the Fahrenheit scale can
be obtained by means of the formula:
9/5 C° + 32 = F°.
--_Trans._
II.
DETECTION OF POISONS, THE PRESENCE OF WHICH IS SUSPECTED.
DETECTION OF ARSENIC.
It is frequently required, in chemical jurisprudence, to institute a
search for arsenic in the remains of a deceased person, whose death is
supposed to have been caused by the reception of a poison. Under these
circumstances the poison is mixed with a mass of substances which would
obscure its characteristic properties, and it becomes necessary, in
order to accomplish its identification, to isolate it, and then, by
decisive reactions, determine its character. Three methods exist which
permit of this result; they are:
1st. The method used prior to Marsh's test.
2nd. Marsh's test.
3rd. A method more recent than Marsh's, proposed by _M. Raspail_.
METHOD USED PRIOR TO MARSH'S TEST.
The materials supposed to contain arsenic are boiled in water which
has been rendered strongly alkaline by the addition of pure potassa. The
fluid is then filtered, an excess of hydrochloric acid added, and a
current of sulphuretted hydrogen conducted through it. If arsenic be
present in the suspected fluid, it is soon precipitated as a yellow
sulphide. In dilute solutions the formation of the precipitate fails to
take place immediately, and only a yellow coloration of the fluid is
perceptible; upon slightly boiling the solution, however, the
precipitation of the sulphide is soon induced. The precipitate is
collected on a filter, well washed with boiling water, and then removed,
if present in a quantity sufficient to admit of this operation. It is
next dissolved in ammonia,[B] and the solution so obtained subsequently
evaporated to dryness on a watch-glass. The residue of sulphide of
arsenic is placed in a tube closed at one end containing nitrate of
potassa in a state of fusion: it is decomposed by this treatment into a
mixture of sulphate and arsenate of potassa, the reaction being
completed in about fifteen minutes. The mixture is now dissolved in
water, and lime water added to the solution: a precipitate of arsenate
of lime is formed, which is separated from the fluid by filtration,
dried, mixed with charcoal, and introduced into a second tube. A few
pieces of charcoal are then placed in the tube adjoining the mixture and
exposed to a red heat, the part of the tube containing the arsenical
compound being also heated. By this operation the arsenic acid is
reduced to arsenic, which is deposited upon the cold portion of the tube
in the form of a metallic mirror. This mirror is then identified by
subsequent reactions. The method just described is no longer in use,
although the precipitation of the arsenic by sulphuretted hydrogen is
still often resorted to in its separation from the other metals with
which it may be mixed. The destruction of the organic substances is,
however, accomplished by means of chlorate of potassa and hydrochloric
acid. To insure the complete precipitation of the arsenic, it is
advisable to conduct sulphuretted hydrogen through the solution, at a
temperature of 70° for twelve hours, and then allow the fluid to remain
in a moderately warm place, until the odor of the gas is no longer
perceptible, the vessel being simply covered with a piece of paper. The
precipitate is next freed from the other metals possibly present, as
directed in the general method of analysis, collected on a filter, and
dissolved in ammonia. The ammoniacal solution is evaporated on a watch
crystal, as previously described, and the residuary sulphide reduced to
metallic arsenic. This reduction is effected by a process somewhat
different from the one previously mentioned: the residue is fused, in a
current of carbonic acid gas, with a mixture of carbonate of soda and
cyanide of potassium. The apparatus employed is represented in Fig. 3:
_a_, is an apparatus producing a constant supply of carbonic acid. Upon
opening Mohr's clamp, _g_, the gas passes into the flask _h_, which
contains sulphuric acid; it is then conducted, by means of the tube _i_,
into the reduction tube _k_, which has an interior diameter of 8 mm.
This tube is represented, in half size, in Fig 4.
[B] The sulphur, usually accompanying the precipitate of sulphide of
arsenic, is insoluble in ammonia.--_Trans._
[Illustration: Fig. 3.]
[Illustration: Fig. 4.]
The reduction is performed as follows: The sulphide of arsenic is
ground in a small mortar, previously warmed, together with 12 parts of a
mixture consisting of 3 parts of carbonate of soda and 1 part of cyanide
of potassium, both salts being perfectly dry. The powder thus obtained
is placed upon a piece of paper rolled in the form of a gutter, and
introduced into the reduction tube. The latter is then turned half round
its axis, so as to cause the mixture to fall in _de_ without soiling the
other parts of the tube. The paper is now withdrawn and the apparatus
mounted. Upon opening the clamp _g_, and strongly heating the mixture by
either the flame of a gas or an alcohol lamp, a mirror-like ring of
metallic arsenic is deposited at _h_, if this poison be present in the
substances under examination. When the coating is too minute to permit
of perfect identification, it should be driven by heat to a thinner part
of the tube; in this way it is rendered easily visible, being condensed
upon a smaller space.
The above process possesses the advantage of not allowing arsenic to be
confounded with any other body; it also permits of a quantitative
estimation of the poison present. For this purpose, it is only necessary
to previously weigh the watch-crystal, upon which the ammoniacal
solution of sulphide of arsenic was evaporated, and to determine its
increased weight after the evaporation; the difference of the two
weighings multiplied by 0.8049, gives the corresponding weight of
arsenious acid, and by 0.6098, the weight of the corresponding amount of
metallic arsenic.
MARSH'S TEST.
Marsh's test is based upon the reduction of arsenious and arsenic acids
by nascent hydrogen, and the subsequent transformation of these bodies
into water and arsenetted hydrogen, a compound from which the arsenic
can be readily isolated. When pure hydrogen is generated in a flask
having two openings, one of which is provided with a perforated cork
through which a safety-tube passes, the other with a tube bent at a
right angle and drawn out to a small point at the free extremity, the
evolved gas, if ignited, burns with a pale non-luminous flame. The air
should be completely expelled from the apparatus before igniting the
gas. Upon bringing a cold porcelain saucer in contact with the point of
the flame, only water is formed. If, however, a small quantity of a
solution containing arsenious or arsenic acids is introduced into the
apparatus by means of the safety-tube, arsenetted hydrogen is produced.
This gas burns with a bright flame, yielding fumes of arsenious acid. In
case a large amount of the poison is present, it can be recognized by
the appearance of the flame, and by inclining a glass tube towards it
upon which a portion of the arsenious acid becomes deposited. These
indications are, however, not distinguishable in presence of only a
small amount of arsenic, and the following distinctive properties of the
gas should be verified:
1st. At an elevated temperature it is decomposed into its two
constituent elements.
[Illustration: Fig. 5.]
[Illustration: Fig. 6.]
2nd. The combustibility of the constituents differs: the arsenic being
less combustible than the hydrogen, begins to burn only after the
complete consumption of the latter body has taken place. For this reason
the flame (Fig. 5) is composed of a dark portion _O_ and a luminous
portion _I_, which surrounds the first. The maximum temperature exists
in _O_ at the point of union of the two parts of the flame. Owing to an
insufficient supply of oxygen, the complete combustion of the arsenic in
this part of the flame is impossible, and if it be intersected by the
cold surface _A B_, that body is deposited as a brown spot, possessing a
metallic lustre. The metallic deposit originates, therefore, from the
decomposition of the arsenetted hydrogen by heat and from its incomplete
combustion. If the spot is not large, it fails to exhibit a metallic
lustre; an experienced chemist, however, will be able to identify it by
the aid of proper tests. Spots are sometimes obtained when the substance
under examination does not contain the least trace of arsenic. These may
be caused by antimony or by a portion of the zinc salt in the generating
flask being carried over by the gaseous current. This difficulty is
remedied by giving the apparatus the form represented in Fig. 6. _A_ is
the flask in which the gas is generated. The delivery-tube _I_ connects
with a second tube _H_, filled with asbestus or cotton; this is united
by means of a cork with a third tube _C_, made of Bohemian glass. The
latter tube is quite long, and terminates in a jet at its free end,
enclosed in tin-foil;[C] it passes through the sheet-iron furnace _R_,
supported upon _G_. The screen _D_ protects the portion _D E_ of the
tube _C_ from the heat. The gas disengaged is ignited at _E_ and the
porcelain dish _P_ is held by the hand in contact with the flame. The
apparatus being mounted, zinc, water and some sulphuric acid are placed
in the generating flask,[D] and the solution containing arsenious acid
added: the evolution of gas commences immediately. The tube _H_ serves
to retain any liquids that may be held suspended. The gas then passes
through the part _C D_ of the tube _C_, which is heated by placing a few
live coals upon the furnace _R_. The greater portion of the arsenetted
hydrogen is decomposed here, and is deposited on the cold part of the
tube, in a mirror-like ring. The small quantity of gas that escapes
decomposition, if ignited at _E_, produces a metallic spot on the dish
_P_. In order to determine that the spots are due to the presence of
arsenic, and not produced by antimony, the following tests should be
applied:
[C] The fusing of the point of the tube is also prevented by
platinizing it. The tube is drawn out, its end roughened by filing,
and then immersed in solution of bichloride of platinum, so that a
drop or two of the fluid adheres. The point, upon heating, now
acquires a fine metallic lustre, and by repeating the operation a few
times a good coating of platinum is produced both on the exterior and
interior of the tube.--_Trans._
[D] The addition of a few drops of solution of bichloride of platinum
to the mixture of zinc, water and sulphuric acid is
advisable.--_Trans._
1. The color of the spots is distinctive: arsenical spots are brown and
exhibit a metallic lustre, whereas those originating from antimony
possess a black color, especially near their border. This difference is,
however, not perceptible when the deposits have a large surface.
2. If the mirror be arsenical, it is readily volatilized from one part
of the tube to another, when the latter is heated, and a current of
hydrogen, or carbonic acid gas made to pass through it. Spots that are
due to the presence of antimony are much less volatile.
3. If the tube is held in an inclined position so that a current of air
traverses it, and the part containing the arsenical mirror heated, the
arsenic oxidizes and arsenious acid is sublimed and deposited higher up
in the tube in the form of a ring, which exhibits octahedral crystals
when examined with a magnifying glass. This ring should be further
tested as follows:
_a._ If it is dissolved in a drop of hydrochloric acid and a solution
of sulphuretted hydrogen added, a yellow precipitate of sulphide of
arsenic is formed. This compound is soluble in ammonia and in alkaline
sulphides, but insoluble in hydrochloric acid.
_b._ If the ring is dissolved in pure water and an ammoniacal solution
of sulphate of copper added, a beautiful green precipitate ("_Scheele's
green_"), consisting of arsenite of copper, is produced.
4. When produced by arsenic the spots are soluble in nitric acid, and
upon evaporating the solution so obtained to dryness, a residue of
arsenic acid, which is easily soluble in water, remains. If an
ammoniacal solution of nitrate of silver is added to the aqueous
solution of the residue, a brick-red precipitate is produced. Spots
consisting of antimony give, when treated with nitric acid, a residue of
an intermediate oxide, insoluble in water.
5. Upon treating the spots with a drop of solution of sulphide of
ammonium, the sulphide of the metal present is formed: if sulphide of
arsenic is produced its properties, as enumerated above, can be
recognized. It may be added that the sulphide of antimony formed is
soluble in hydrochloric acid, and possesses an orange red color, whereas
sulphide of arsenic is yellow.
6. When spots originating from arsenic are treated with a solution of
hypochlorite of soda (prepared by passing chlorine into solution of
carbonate of soda), they are immediately dissolved; if, on the other
hand, they are produced by antimony, they remain unaltered by this
treatment.
Such are the properties exhibited by soluble compounds of arsenic when
treated by Marsh's process; the following precautions are, however,
necessary when this test is made use of in medico-legal examinations.
1. If small white gritty particles, resembling arsenious acid, are
discovered in the stomach or intestines, they are directly introduced
into Marsh's apparatus. When this is not the case, the destruction of
the organic matter is indispensable even though, instead of the organs
themselves, the contents of the alimentary canal are taken. In the
latter instance, the solids are separated from the fluids present by
filtration, the solution evaporated to dryness and the residue united
with the solid portion; the organic matter is then destroyed by one of
the methods previously described. In the special case of arsenic, the
separation of the poison from the accompanying organic materials can be
accomplished by a process not yet mentioned which may prove to be of
service. The suspected substances are distilled with common salt and
concentrated sulphuric acid. By this operation the arsenic is converted
into a volatile chloride which distils over. The poison is isolated by
treating this compound with water, by which it is decomposed into
hydrochloric and arsenious acids. We must give preference, however, to
the method by means of chlorate of potassa and hydrochloric acid.
2. The solution having been obtained in a condition suitable for
examination, the air is completely expelled from the apparatus by
allowing the gas to evolve for some time, and the suspected fluid then
introduced into the generating flask. Danger of explosion would be
incurred were the gas ignited when mixed with air.[E]
[E] The effervescence of the mixture is prevented by _slowly_ adding
the arsenical solution to the generating flask. In order to avoid loss
of arsenetted hydrogen, the cold dish should be directly applied to
the flame even before the introduction of the suspected solution, and
its position changed at short intervals, so as to allow the deposit to
be formed on different parts.-_Trans._
3. It is indispensable, in applying this test, to have a second
apparatus in which only the reagents necessary to generate hydrogen are
placed: in this way, if no spots are now produced by the use of the
second apparatus, it is certain that those obtained when the first
apparatus is employed do not originate from impurities present in the
reagents used.
It has come under the author's observation, however, that a sheet of
zinc sometimes contains arsenic in one part and not in another; in fact,
the shavings of this metal, as purchased for laboratory use, are often
taken from lots previously collected, and may therefore have been
prepared from several different sheets. If this be the case, it is
supposable that the zinc used in the second apparatus may be free from
arsenic, whereas the metal with which the suspected solution is brought
in contact may contain this poison; serious danger would then exist of
finding indications of the presence of arsenic in materials that did not
originally contain a trace of the metal. In order to obviate this
important objection, which might possibly place a human life in
jeopardy, we propose the following modifications: Pure mercury is
distilled and its absolute purity established. As the metal is a fluid
and is therefore homogeneous, it is evident if one portion be found
pure, the entire mass is so. Sodium is then fused under oil of naphtha,
in order to cause the complete admixture of its particles, and the
purity of the fused metal in regard to arsenic tested. An amalgam is
next prepared by uniting the mercury and sodium. This is eminently
adapted to toxicological investigations: in order to generate a supply
of very pure hydrogen, it is only necessary to place the amalgam in
water kept slightly acid by the addition of a few drops of sulphuric
acid, by means of which the disengagement of gas is rendered more
energetic.[F]
[F] Owing to the impurities often occurring in zinc, the use of
distilled magnesium in Marsh's apparatus has also been suggested. This
metal is now to be obtained in a state of great purity; it is,
however, sometimes contaminated with silicium, which body likewise
gives rise to a metallic deposit, but one that is readily
distinguished from arsenical spots by its insolubility in nitric acid,
_aqua regia_, and in hypochlorite of soda. The presence of magnesium
causes the precipitation of the non-volatile metals possibly contained
in the fluid tested for arsenic.--_Trans._
It should be borne in mind that the solution introduced into Marsh's
apparatus must not contain organic substances, and that, in case their
destruction has been accomplished by means of nitric acid all traces of
this compound are to be removed. The sulphuric acid used should also be
completely freed from nitrous vapors. According to _M. Blondeau_,
nascent hydrogen in the presence of nitrous compounds converts the acids
of arsenic not into arsenetted hydrogen (As H{3}), but into the _solid_
arsenide of hydrogen (As{4} H{2}). This latter compound, upon which pure
nascent hydrogen has no effect, is transformed into gaseous arsenetted
hydrogen by the simultaneous action of nascent hydrogen and organic
substances. These facts are of the greatest importance, for they might
possibly cause a loss of arsenic when it is present, as well as
determine its discovery when it is absent.
The first case is supposable: should traces of nitric acid remain in
the solution, the arsenic would be transformed into solid arsenide of
hydrogen and its detection rendered impossible. The second case may also
occur: if the zinc placed in the apparatus contains arsenic, and the
sulphuric acid used contains nitrous compounds, the evolved gas will
fail to exhibit any evidence of the presence of arsenic, owing to the
formation of the solid arsenide of hydrogen. Upon adding the suspected
solution, which, perchance, may still contain organic substances, this
arsenide is converted into arsenetted hydrogen, and the presence of
arsenic will be detected, although the solution under examination was
originally free from this metal.
RASPAIL'S METHOD.
M. Raspail suggests the following method for detecting arsenic: The
surface of a brass plate is rasped by filing. In this condition the
plate may be regarded as an innumerable quantity of voltaic elements,
formed by the juxtaposition of the molecules of zinc and copper. The
suspected materials are boiled with caustic potassa, the solution
filtered, a drop of the filtrate placed upon the brass plate, and a drop
of chlorine water added. If the plate is then allowed to stand for a
moment and the substance under examination contains arsenic, a
mirror-like spot is soon deposited upon its surface. In order to avoid
confounding this deposit with those produced by other metals, the
substitution of granulated brass for the plate is in some cases
advisable. The granulated metal is dipped successively in the suspected
solution and in chlorine water. The granules retain a small quantity of
the solutions and, owing to the action of the chlorine water, become
covered with metallic spots, if arsenic be present. They are then dried,
placed in a tube closed at one end, and exposed to the heat of an
alcohol lamp. In case the spots are arsenical, the metal volatilizes and
condenses in a ring upon the cold part of the tube, which is submitted
to the tests previously described.
This method can hardly be of great service, inasmuch as it extracts the
poison from but a very small portion of the solution containing it: we
have not, however, personally tested its merits.[G]
[G] The omission in the text of Reinsch's test should be supplied.
This test is based upon the fact that when solutions of arsenious acid
or an arsenide are acidulated with hydrochloric acid and boiled with
metallic copper, the latter becomes covered with a film consisting
largely of metallic arsenic: it is extensively employed in
chemico-legal examinations. The materials to be examined are
completely disintegrated by boiling with hydrochloric acid, and the
fluid filtered. Some pure copper gauze or foil, having a polished
surface, is then immersed in the boiling solution, and notice taken of
the formation of a grey deposit. If a coating be formed, fresh pieces
of the metal are added, so long as they become affected. The copper is
then withdrawn from the solution, thoroughly washed with water, and
dried, either by means of the water-bath or by pressing between
bibulous paper. It is next introduced into a dry tube, and heated over
a spirit lamp. The arsenic present volatilizes and is oxidized to
arsenious acid which forms a deposit, consisting of octahedral
crystals, on the cold part of the tubes. These are subsequently tested
by means of the reactions distinctive of arsenious acid. It need
hardly be added that the absolute purity of both the hydrochloric acid
and of the copper is to be carefully established. The deposit obtained
in the above operation was formerly regarded as pure arsenic, but it
has been proved to be an alloy consisting of 32 per cent. arsenic, and
68 per cent. copper. Reinsch's test possesses the advantage of
requiring but little time for its execution, of being applicable to
complex organic mixtures, and of effecting the detection of a very
minute trace of the poison.--_Trans._
DETECTION OF ANTIMONY.
Strictly speaking the salts of antimony are more therapeutic than
poisonous in their action. In fact they usually act as emetics and,
under certain circumstances, may be taken in large doses without
incurring serious results. There are instances, however, in which their
action is truly toxical, and it becomes necessary to effect their
detection in the organs of a body. It should be remarked that these
salts, if absorbed, remain by a kind of predilection in the liver and
spleen. A special examination of these organs should therefore be
instituted, particularly if the fluids of the alimentary canal are not
at hand, which is frequently the case when some time has elapsed before
the investigation is undertaken.