Nature of Chemistry. There is an almost endless
diversity among the various objects by which mankind
is surrounded ; but one property, at least, they possess
in common, and that is the property of weight. All
objects are attracted by the earth, and the reason why a
thing is heavy is that this earth-attraction, known as
gravitation, offers the resistance called weight to any
efforts to raise things from its surface. This property
of weight characterizes not only solid substances like
iron or wood, but likewise liquids, such as water and oil,
and also gases, of which atmospheric air is an example.
It is convenient to have one name that shall include all
such bodies, and for this purpose the term matter is
employed. Matter, then, is anything which possesses
weight, i.e. is acted on by gravitation.
It is now easy to explain the objects of chemistry.
Matter is not only most varied in form, but its form is
also continually varying; it is the function of the
chemist to investigate these different forms of matter
and also the changes to which they are subject. These
may be summed up in the following definition :
Chemistry is that science which treats of the composition
of matter, of the changes produced therein by heat and
other natural forces, and of the action and reaction of
different kinds of matter on each other.
The composition of matter embraces all questions of
analysis.
The action of forces on matter, and of different kinds
of matter on each other, include the science of chemical
processes and manufactures.
The study of the nature and action of drugs is ex-
pressly included in the domain of chemistry. The
Institute of Chemistry is the governing body of the
chemical profession ; and, among its other functions, is
an examining body. As such it examines chemists
in Therapeutics and Pharmacology. These subjects
include " Uses of the commoner drugs . . . how far the
impurities affect the medicinal value of the drugs ; the
chemical changes which familiar drugs may undergo in
the body . . . the reputed medicinal, deleterious, and
average fatal doses of such drugs as are poisonous ; and
the reputed effects of age, idiosyncrasy, and habituation
in modifying these."
Forensic Chemistry. The qualifying word "forensic"
implies that which appertains to the proceedings of
Courts of Justice. Forensic chemistry may therefore
be regarded as including all those branches of chemistry
which are of service in solving the various questions
that arise during the course of judicial proceedings.
Thus in the administration of the Food and Drugs Acts
their whole operation depends on the results of analysis.
The same remark applies with almost equal force to
many criminal actions, of which murder by poison is
the most striking example. In civil cases too, chemistry
often plays an important part; and in such litigation as
that involved in patent actions, the chemistry of manu-
facturing processes is examined most exhaustively. A
complete treatise on forensic chemistry would therefore
have at least to deal with all the general principles of
chemistry, all analytical methods, and all processes of
chemical manufactures, in so far as they apply to the
solution of judicial problems. It is scarcely too much
to say that it would in fact require to be co-extensive
with the science of chemistry itself. Such ambitious
aims are not compatible with the scope of the present
work, which, as already intimated, owes its origin to a
course of lectures on forensic chemistry. Obviously, a
small portion only of the subject could be treated
within such limitations, and choice fell upon " chemical
evidence, its preparation and adduction." The subject-
matter of these lectures, with certain enlargements and
additions, forms also the subject-matter of this book.
Nature of Evidence. In all legal proceedings the
first essential is that the facts of the matter in dispute
shall be brought to the knowledge of the Court in the
most authentic form possible. This is done by the
giving of evidence, and evidence may be regarded as-
that by which facts are proved in the course of legal
proceedings. The Court is entitled to the very best
evidence that can be obtained, and when it is available
will usually insist on that of eye-witnesses, who are
required to come personally to the Court and there state
exactly what they have seen, or facts which are within
their personal knowledge. The correctness of their
evidence can then be tested by questions put on behalf
of all the parties, and, should he deem it necessary,
by the judge himself. Witnesses are frequently
required to bring with them and produce books or
other documents. They may also produce and show
to the Court objects which serve to explain or elucidate
their evidence.
In certain cases evidence may be given in writing, the
document, according to circumstances, being then known
either as a " statutory declaration " or an " affidavit." It
is specially enacted by the Food and Drugs Acts that a
certificate of analysis given by a Public Analyst may be
produced in Court and used as evidence.
Burden of Proof. It is the duty of the party who
alleges the affirmative case to prove that case. Such
party is generally the prosecutor or plaintiff. Thus, if
milk is said to be adulterated, the prosecutor must prove
the fact of adulteration. If the Crown accuses the
prisoner in the dock of having poisoned a man, the
Crown must prove that the man was in fact poisoned
by the prisoner. At times the burden of proof shifts
from one party to the other, and of this an illustration
is afforded in the working of the Adulteration Acts.
The Board of Agriculture is empowered to make
regulations determining what deficiency in any of the
normal constituents of genuine milk, and other articles
specified, shall raise a presumption, until the contrary
is proved, that the milk is not genuine. On the
prosecution proving such deficiency, the further burden
of proof is on the accused person, who must show by
sufficient evidence that the milk is in fact genuine.
It may be taken as an absolute rule that the evidence
must be complete and conclusive. A very general
defence is that the evidence is incomplete and incon-
clusive. Although this may at times seem to operate
hardly against those on whom the burden of proof rests,
yet a little consideration will show the rule to be a fair
one. The defence has a perfect right to succeed if at
any one point the chain of proof breaks.
Chemical Evidence. Chemical evidence is that
which deals with chemical facts and deductions. In
general, such evidence is governed by the same rules
as apply to other evidence. To this there is one
important exception. The ordinary witness as to fact
is not allowed to give his opinion. He may state that
he saw the body of a man in a pool of water, but his
opinion that some one must therefore have thrown him
in is not evidence. But the expert witness, in which
class is included the chemist, has a somewhat wider
latitude permitted him. It was held in Folkes v. Chad
(Cockle's Leading Cases on Evidence) as early as 1782
by MANSFIELD, C. J., that " In matters such as those of
science, expert witnesses may give evidence as to their
opinion." The chemist may therefore state not merely
his facts, but also the deductions he has drawn from
them, and the opinions he has formed thereon.
Functions of Chemist and Lawyer. Although
both chemist and lawyer are concerned in the pre-
paration and formulation of chemical evidence, they
are not necessarily familiar with each other's methods
and requirements. The chemist will often wish that
he could get the lawyer to understand something at
least of the processes by which he arrives at his results,
so that the latter may realise more clearly the actual
nature and value of the evidence he is prepared to give.
The lawyer to whom a chemical report or certificate is
sent will frequently regret that such a report contains
much that is useless to him for his particular purpose,
while perhaps something absolutely necessary in order
to comply with a legal technicality is altogether
wanting. It follows that the chemist should know
sufficient of the rules of evidence to make his analyses
or experiments as useful as possible to the lawyer. To
the latter it is an immense advantage to be able to
understand something of the principles underlying the
processes by which the chemist arrives at his con-
clusions. The author's primary object in this work is
therefore to make clear to both chemists and lawyers
matters which are common ground to both professions,
and to render them sufficiently plain for the members
of each to understand, where they overlap, the work of
the other. Taking these in their natural sequence, the
principles of chemical work and analysis will first
demand consideration.
Chemical Analysis, Definition of. For the present
purpose this may be regarded as including all methods
of ascertaining and determining the composition in
whole or in part of the substance in issue.
IMPORTANT CONSIDERATIONS IN SUCH ANALYSIS.
I, Collection of Fair Samples. The taking of,
samples is in itself a matter requiring much care, and
frequently presenting considerable difficulty. Thus the
contents of a vessel may vary in composition according
to the part from which taken. For example, one part
of a barrel of butter may contain a larger proportion
of water than another. Or in a parcel of ore some
pieces may be much richer in metal than are others.
In all these cases the sample should be so taken as to
represent as nearly as possible the average quality of
the whole bulk. The chemist should himself take the
sample ; or some other person, skilled in the art of
sampling the particular product, should take it for the
purpose of analysis. The analyst will personally see to
it that his sample is uniformly mixed before he takes
portions for his analysis.
In certain bodies there is always a natural tendency
toward separation. A good example of these is milk :
the fat or cream is lighter than the remainder of the
milk, and so rises to the surface. This is remedied by
thoroughly shaking or stirring before taking the sample.
In case the sample is obtained by the ordinary method
of purchase, the responsibility for its quality rests on
the vendor. He cannot shield himself by proving that
the bulk is much richer than was the actual lot sold-
But the buyer, before dividing his purchase into parts,
should take care that each part is of the same
composition.
The point of separation of a sample was raised in a
recent case, Tucker v. Hayes and Finch, 1908. In that
case a sample was taken of a cake of candle-wax, and
submitted to analysis. In cross-examination, the chemist,
Hehner, was asked whether certain of the constituents
might not, during the solidification of the melted mass,
have first separated out and fallen to the bottom, thus
causing the upper layer to be of different composition
from the lower. In reply, the analyst was able to say
that from the nature of the constituents no such
separation could occur.
II, Changes in Sample. In the case of perishable
articles considerable changes may take place in the
substances after the purchase and before the sample
has reached the analyst. Thus milk may go sour, and
in extreme cases may lose some portion of its solid
matter by its conversion into gases as a result of
fermentation. This property is recognised by the
Food and Drugs Acts, and in the case of a certificate
regarding milk, butter, or any article liable to decom-
position, the analyst is required to specially report
whether any change had taken place in the constitution
of the article that would interfere with the analysis.
The excise laws permit the sale of non-intoxicating
beers, as for example ginger beer and the so-called
herb beers, free of duty, provided the amount of alcohol
they contain does not exceed 2 per cent, of proof
spirit. These non-excisable beers are prepared by a
process of fermentation in which sugar is changed by
yeast into alcohol and carbon dioxide gas, just the
same as in ordinary beers. In order to prevent the
alcohol exceeding the excise limit, the quantity of
sugar must be carefully regulated and the fermenta-
tion arrested when sufficient alcohol has been produced.
The resultant beer has usually some unchanged sugar
left in it as a flavouring matter. If the beer has
simply been sterilised, and untreated with a preserva-
tive, the accidental introduction of some fresh yeast
may again set up fermentation, and thus increase the
percentage of alcohol present to an amount beyond
the permitted limit. From time to time the excise
authorities purchase samples of non-excisable beers
and submit them to analysis.- In the case of excess of
alcohol, a possible line of defence is that fermentation
has occurred during the period between purchase and
analysis, and consequently the excess at the latter
date is not conclusive proof of excess of alcohol at the
time of sale. Under such circumstances an analyst,
if pressed, would probably admit that such a change
was possible though exceedingly improbable. In
anticipation of such defence, the analyst should
observe carefully the condition of the sample when
submitted to him i.e., whether quiescent or in a state
of fermentation. If considered necessary, the beer
may be examined for living yeast cells, and also for
the presence or absence of sufficiency of preservative
to inhibit fermentation. Positive evidence may thus
be obtained which will negative the defence of after-
fermentation if raised. On the other hand, such
defence may be considerably strengthened by showing
that other bottles of the same batch (as well as a
portion of the sample taken for analysis) were in
active fermentation, or in such a condition that, on
opening, active fermentation was promptly set up.
III. Methods of Analysis, Principles of. The
methods of analysis may be conveniently divided into
two groups, namely, those of Direct and Indirect
methods.
Direct Methods.
(1) Separation, recovery, and determination of the
essential constituent. For example, fat from milk, or
arsenic from a body suspected of being poisonous.
(2) Separation, recovery, and determination of some
body which is a measure of the essential constituent.
For example, butter fat contains certain volatile acids.
The separation and estimation of these afford a measure
of the quantity of butter fat in a mixture of fats.
(3) Production, separation, recovery, and determina-
tion of some body containing a definite proportion of
the essential constituent, or some component of the
essential constituent. For example, from a substance
containing potassium phosphate, magnesium phosphate
may be obtained by precipitation and determined.
Magnesium phosphate contains a definite proportion of
anhydrous phosphoric acid, or phosphoric anhydride,
and so the amount of that body in the original substance
is ascertained.
Indirect Methods.
(1) Determination of physical characteristics. For
example, specific gravity. Thus water has a specific
gravity of TOOOO, and pure alcohol of 07935. Mixtures
of water and alcohol have intermediate specific gravities,
and as all potable spirits are mixtures of alcohol and
water the determination of the specific gravity affords
a means of ascertaining the proportions of alcohol and
water present. It is obvious that for such methods to
be trustworthy there must be no other disturbing body
in the substance. In the case of ordinary spirits, such
as whisky or gin, there are only traces of bodies other
other than alcohol and water present, and these do not
materially interfere with the results. With beers it is
different, and so all the spirit and some of the water are
first separated by distillation, and then the specific
gravity of the distilled portion (distillate) is taken.
From this, the percentage of alcohol in the beer is
obtained by calculation. If wished for the sake of
greater accuracy, spirits such as gin or whisky may
similarly be first distilled.
Another such mode of analysis is the determination
of the molecular weight of a substance. The chemist
terms the smallest possible particle of a body, which is
capable of existing alone, a molecule ; and the relative
weight of this is termed the molecular weight. Such
molecular weight may be ascertained by chemical
analysis. Suppose a substance is known to consist of
a mixture of two bodies only, one of which has a
molecular weight of 100, and the other of 200 ; and
that the mixed substance has a molecular weight of
150. Obviously, the mixture must consist of equal
quantities of each constituent. With any other inter-
mediate molecular weight, the proportions of each
constituent is simply a matter of calculation. This
mode of analysis was largely employed in the analyses
of candle waxes for the purposes of the case of Tucker
v. Hayes and Finch before referred to.
(2) Determination of some chemical effect which the
essential constituent is capable of producing. For
example, an alkali possesses the power of neutralising
an acid. If a solution of acid of known strength is
prepared, the amount of alkali in a substance under
examination may be ascertained by determining the
quantity of the acid solution it is capable of neutralising.
Conversely, the quantity of acid in a substance may
be determined by the similar employment of a solution
of alkali of known strength. The chemist prepares a
range of such solutions, known as standard or normal
alkalis and acids, and uses them for analytical operations
of this description. Such determinations are known
respectively as alkalimetry and acidimetry. The
whole branch of analysis, termed volumetric analysis,
is based on the estimation of bodies by the use of
standard solutions of known strength and which pro-
duce specific and recognisable chemical changes.
As another example, certain sugars possess the
property of precipating in the insoluble form an oxide
of copper, known as cuprous oxide, from a solution of
copper salts. If, with the requisite precautions, a
solution of a sugar be added to the copper salt solution,
this precipitate is formed and may be separated and
weighed. The amount of the cuprous oxide thus
obtained is a measure of the quantity of the sugar
present in the body under examination. This con-
stitutes the well-known Fehling's Test.
Although the details of methods of chemical analysis
are to the lay mind most complicated and involved,
there is scarcely an operation of analysis which does
not fall either into one or other of the groups described,
or is a combination of two or more of them.
Minute Traces. Occasionally a question is raised
as to the recognition of minute traces. Thus, in some
forms of analysis a return is made of the number of
parts per million of some constituent. An objection
may be taken that accuracy in the determination of
such infinitesimal quantities is impossible, and that,
even if determined, it cannot possibly matter whether
so small a quantity of any particular substance is
present or absent. The first objection can only succeed
when those responsible for the decision are totally
ignorant of the principles of analysis. Parts per
million are by no means difficultly recognisable and
determinable by analytic methods ; and a chemist
may speak with just as much certainty of these
apparently minute quantities as he would of the
number of Ibs. of a body in a cwt. of a mixture. The
latter objection is perhaps more plausible, but equally
fallacious. Brandy should consist entirely of spirit
distilled from wine, which in turn ought only to
consist of the fermented juice of the grape. Brandy
is imitated by taking plain alcohol, colouring and
flavouring it to look and taste something like the
genuine spirit. In making an analysis, the chemist
searches for and estimates some special constituent,
which in genuine brandy is present in only the most
minute quantities, while in the fictitious spirit it is
entirely absent. It may be very likely that the trace
of this body present in the brandy does not materially
affect its quality, and if it could be removed without
any other disturbance, the spirit would not be ap-
preciably altered. This, however, is not the point;
the analyst determines this body because it is evidence
of whether the liquid is brandy or not. If present
in the normal quantity, it goes to prove the spirit is
genuine ; a diminished amount tends to show plain
spirit has been added. If the amount diminishes to
vanishing point, the conclusion is that the spirit
contains no brandy at all. It is in this way that
determinations of constituents, comparatively unim-
portant in themselves, may nevertheless be pregnant
with information as to the purity or otherwise of a
body.
Blank Experiments. Frequently there are un-
avoidable impurities in the chemical reagents used in
an analysis, or there may be errors of experiment
that should be considered and allowed for. A common
method of providing for these is by means of what
is called a " blank experiment." . For example, in what
is known as Kjeldahl's method of determining nitrogen
in organic bodies, the weighed quantity of the sub-
stance is heated in a flask with sulphuric acid and
other reagents until completely decomposed. The
nitrogen is then present in the form of ammonium
sulphate ; from this it is liberated by the addition of
sodium hydrate, and ammonia is distilled off, and
estimated. The quantity of ammonia thus found is-
the measure of the nitrogen in the original body. It
is almost impossible to get the various reagents free
from traces of ammonia. The usual practice is there-
fore to make an experiment exactly like the whole
determination, except that none of the body to be
estimated is used. The sulphuric acid and other
reagents are heated in the flask, and every stage
of the process gone through. At the end, the distilled
ammonia is determined. The quantity should not
be large ; but in practice there is always some
obtained. Whatever the amount may be, this is
used as a correction, and is deducted from that found
in the actual analyses. Such a blank experiment
should be made with each fresh lot of reagents.
But where such blank analyses are made, it must
be remembered that they are " unreliable unless all
the circumstances be thoroughly comprehended and
taken into account." For example, in Crooke's Select
Methods of Analysis, directions are given for the
testing of reagents for arsenic by a blank analysis.
On thus testing ferric chloride it gave no arsenic
reaction, and was apparently pure ; nevertheless
arsenic in considerable quantities was evolved in
the course of an experiment in which this ferric
chloride was used. On subsequently repeating the
blank test on the ferric chloride, but with the addition
of copper or carbon (charcoal), a considerable amount
of arsenic was evolved. The explanation is that the
arsenic in the ferric chloride had to be reduced to the
arsenious form before it would distil off in the
test. (Analyst XV. 16.)
When blank analyses are relied on, they should
be carefully studied from this standpoint, both by the
side submitting the result and by those whose duty it
is to question and, if necessary, attack them.
Such underlying principles as are here described,
if once grasped by the legal mind, should prove of
immense assistance in the understanding and digesting
of analytic evidence.
Range of Chemical Evidence. As already stated,
such evidence is required in a wide range of cases,
such as those arising out of the Food and Drugs Acts,
more important criminal matters, and many civil
causes. It is proposed to illustrate its utilisation by
reference to cases occurring in the administration of
these various branches of the law.
