either by erasing the portion of the writing over the signature and
substituting other matter, or by changing certain words, in order to
modify the signification of a sentence.
Writings are altered either by erasure or by washing. Erasure, although
more easily executed, is seldom employed, as it renders the paper thin
in places, and in this way leaves effects apparent even to the naked
eye, and, although the original thickness can be restored by application
of sandarac or alum, these substances possess properties differing from
those exhibited by paper, and may, moreover, be completely removed, thus
exposing the thinning of the paper.
In case washing by means of chlorine has been resorted to, the
sizing--which renders the paper non-bibulous, and which is only with
difficulty replaced--may have been removed. Formerly paper was sized by
immersion in a solution of gelatine; at present, however, a soap of
resin, or wax, and alumina (a little starch being added) is more
commonly used. In the latter case, the sizing is less easily removed by
the action of water than when the gelatine preparation is employed; the
detection of its attempted restoration is also a matter of less
difficulty, as gelatine would be employed for this purpose, and this
body possesses properties different from those exhibited by the
substances normally contained in paper: iodine, for instance, which
imparts a yellow color to gelatine, turns starch violet-blue. In order
to detect the alteration of a writing, the following examinations are
made:
1º. The paper is carefully examined in all of its parts, and in various
positions, by aid of a lens. In this way, either thinned points, caused
by erasure, or remaining traces of words, may possibly be discovered.
2º. The paper is next placed upon a perfectly clean piece of glass, and
completely and uniformly moistened with water. The glass is then
removed, and the transparency of the paper examined by aid of a lens.
When uniform transparency is exhibited, and certain portions are neither
more transparent nor more opaque than the rest of the paper, it is
probable that erasure has not been attempted. If, on the other hand,
opaque points are observed, it is almost certain that letters have been
erased, and sandarac, which is not affected by water, subsequently
applied. In case transparent points are detected, there is reason to
suspect that words have been removed, and the spots either left intact
or afterwards coated with a substance soluble in water, such as alum.
3º. The paper is dried and the above operation repeated with alcohol of
87 per cent. Indications may now be observed which failed to occur in
the treatment with water; as well as these latter confirmed. As alcohol
dissolves sandarac, the points that formerly appeared opaque may now
become transparent.
4º. The paper is again dried, then placed under a sheet of very thin
silk-paper, and a warm iron passed over it. This operation frequently
causes the reappearance of words that have been partially obliterated.
It is also advisable--as suggested by _M. Lassaigne_--to expose the
paper to the action of iodine vapors. If alteration has not been
attempted, the paper will acquire an uniform color; yellow, if sized
with gelatine; violet blue, if sized with the mixture of soap, resin and
starch. When, on the contrary, a subsequent sizing of gelatine has been
applied in order to mask the alteration--the paper having been
originally sized with the above mixture--it will assume in some portions
a yellow, in others a violet-blue color.
5º. It is ascertained whether the paper possesses an acid reaction. If
so, its acidity may result from the presence of hydrochloric acid, in
case the paper was washed with chlorine, or of other acids. Alum, used
to disguise erasure, would also cause an acid reaction. The mere
detection of acidity is, in itself, of little importance, as, in the
manufacture of paper, the pulp is bleached by means of chlorine, and
this reagent may not have been entirely removed by washing. If, however,
the paper is acid only in certain spots, and these points produce a red
coloration upon blue litmus paper, having the form of letters, the
indication is of value. In order to ascertain if this be the case, it is
advisable, before wetting the paper, to slightly press it upon a sheet
of moist litmus paper: the acid spots will then leave a reddish trace
upon the latter.
6º. The manuscript under examination is again spread upon a glass-plate,
and a solution of tannin (or preferably, a solution of ferrocyanide of
potassium containing one per cent. of the salt, and acidulated with
acetic acid) applied by means of a brush. If the original writing was
executed with ordinary ink (which has as its base tannate of iron), and
the washing has been but imperfectly performed, it is quite possible
that a blue coloration will be produced by the action of the
ferrocyanide. It is, however, often necessary to apply the above
reagents several times before the original writing becomes apparent;
indeed, in some cases months have elapsed before the reaction has
occurred.
In case the alteration or destruction of the document is feared in the
above test, it is well to previously provide the court with a certified
copy, and then proceed with the examination.
7º. If the paper possesses a friable appearance, it has possibly been
washed with sulphuric acid. This property may however originate from
other causes, and the presence of the acid should be confirmed by
washing the document with distilled water, and adding a solution of
chloride of barium to the washings. The precipitate should form in a
considerable quantity, as a slight cloudiness could be due to sulphates
contained in the water used in the preparation of the pulp.
If much sulphuric acid be present, it may be so concentrated by heating
as to cause the carbonization of the paper.
8º. It is also well, should washing with sulphuric acid be suspected, to
ascertain, by aid of a lens, if the filaments on the surface of the
manuscript possess an inflated appearance. This would be caused by the
escape of carbonic acid, originating from the action of sulphuric acid
upon the carbonates contained in the water used in the manufacture of
the paper.
9º. Old ink is more difficult to remove than new, and it is therefore
sometimes possible to cause the reappearance of old writings, over which
words have been subsequently written. For this purpose, a solution
containing 50 per cent. of oxalic acid is applied with a fine brush over
the suspected points. As soon as the ink disappears, the acid is
immediately removed by washing with water, and the paper dried. Upon now
repeating the operation, the presence of a former writing may be
detected after the complete disappearance of the words last written.
10º. According to _M. Lassaigne_, when the same ink has not been used
throughout a document, washing with dilute hydrochloric acid will
demonstrate the fact. This acid, while causing the gradual obliteration
of characters written with ordinary ink--the shade of the paper not
being altered--produces a red color, if ink containing log-wood has been
employed, and a green coloration, in case the ink used contained
Prussian blue.
The expert may possibly be called upon to give evidence as to the
existence of a "_trompe-l'oeil_;" as was the case in the trial of _M. de
Preigne_, which took place at Montpelier in 1852. A "_trompe-l'oeil_"
consists of two sheets of paper, glued together at the edges, but having
the upper sheet shorter than the other which therefore extends below it.
This species of fraud is executed by writing unimportant matter on the
uppermost sheet, and then obtaining the desired signature, care being
taken that it is written on the portion of the paper projecting below.
The signature having been procured, it is only necessary to detach the
two sheets in order to obtain a blank paper containing the signature,
over which whatever is desired can be inserted. The trial referred to
above, was in reference to a receipt for 3,000 francs. The expert, upon
placing pieces of moistened paper upon the suspected document, noticed
that they adhered to certain points, and that these formed a border
around the paper but passing _above_ the signature. The fraudulency of
the act was thus established, and so recognized by the court, although
the accused was acquitted by the jury.
Numerous means have been proposed, in order to render the falsification
of documents a matter of difficulty. The most reliable of these is the
use of "Grimpe's safety-paper," containing microscopic figures, the
reproduction of which is impossible. Unfortunately, up to the present,
the government has adopted methods less sure.
EXAMINATION OF WRITINGS IN CASES WHERE A SYMPATHETIC INK HAS BEEN
USED.
Sympathetic inks are those which, although invisible at the time of
writing, become apparent by the application of certain agents. They are
of two classes: those which are rendered visible by the mere application
of heat, such as chloride of cobalt, or the juice of onions; and those
which are brought out only by the action of a reagent. The inks of the
second class most frequently used are solutions of acetates of lead, and
other metals which give a colored sulphide when treated with
sulphuretted hydrogen. Characters written with a solution of
ferrocyanide of potassium acquire a blue color, if washed with a
solution of perchloride of iron. It is scarcely necessary to add that
the latter solution can be used as the ink, and the ferrocyanide as the
developer.
When the presence of characters written with a sympathetic ink is
suspected, the document is examined as follows:
1. The paper is at first warmed: if the ink used is of the first class,
the characters will now become legible; otherwise the examination is
continued as below.
2. The paper is exposed to the action of steam, in order to moisten the
ink present (care being taken to avoid dissolving the characters), and a
current of sulphuretted hydrogen allowed to act upon it. If the ink used
consists of a lead, bismuth, or gold salt, a black coloration will
ensue; if salts of cadmium or arsenic were employed, the characters will
acquire a yellow color; if, finally, a salt of antimony was used, a red
coloration will be produced.
3. If no coloration was caused by the action of sulphuretted hydrogen,
it is probably that either a solution of ferrocyanide of potassium or a
persalt of iron has been resorted to. Each of these solutions is
separately applied on a small portion of paper by means of a brush, and
notice taken if the characters become visible. The solution that
produced the change is then applied over the entire sheet.
4. In case only negative results were obtained in the preceding
operations, it must not yet be concluded that a sympathetic ink has not
been used, although we are left without further recourse to chemical
tests. Numerous organic compounds may have been resorted to, the
detection of which is almost impossible; moreover, if a mistake was made
in regard to the preparation supposed to have been used, the reagents
employed for its detection may render the discovery of another ink
absolutely impossible. It is therefore often necessary to apply
mechanical tests. For this purpose, the paper is spread upon a glass
plate, uniformly moistened with water, and a second plate placed over
it: if the characters were written with a pulverulent substance
suspended in water or mucilage, they may often be observed upon
examining the transparency of the paper. In case the substance used is
both colorless and soluble, the detection of the written characters will
be more difficult; still, indelible traces may possibly have been left
by the pen. If, however, the ink employed is a colorless and transparent
organic compound of rare occurrence, and was applied with a fine
pencil-brush which failed to affect the paper, it must be acknowledged
that little or nothing can be definitely determined as to its presence
or absence.
FALSIFICATION OF COINS AND ALLOYS.
In all civilized countries a fixed standard for coins and precious
alloys is established by law, in order to prevent the perpetration of
frauds which would be of serious injury to the public welfare. The
substitution of coins consisting of an alloy inferior in value to the
standard fixed by law, is too advantageous a fraud not to be often
attempted.
Coins are most frequently altered by _clipping_; by _stuffing_, that is,
by boring the coin and inserting an alloy of small value; by _doubling_,
which operation consists in covering its face with two thin laminæ taken
from a genuine coin; and by applying a coating of gold or silver by
means of electro-plating.
In order to ascertain if a coin has been counterfeited, its weight
should at first be determined. If it has been clipped, or consists of an
alloy possessing a density less than that of silver or gold, the fact is
immediately demonstrated by its decreased gravity.
The coin is further tested by throwing it down upon a hard substance:
gold and silver give a ringing sound, whereas the majority of other
metals produce a dull sound.
The result obtained by this latter test often fails to be reliable. A
skilful counterfeiter may prepare an alloy equally sonorous and heavy as
silver or gold; in fact, _M. Duloz_ exhibited to the author an alloy,
prepared by him, possessing the density, sonorousness and lustre of
silver; the composition of which, for obvious reasons, has not been
published.
In instances of this nature the fusibility of the coin should be
determined, and the result obtained compared with the melting point of
the legal alloy, or, this failing, a chemical analysis executed. In
order to perform the latter test, the coin under examination is boiled
with nitric acid: all metals are dissolved, with exception of gold and
platinum, which remain unaltered, and tin and antimony, which are
converted respectively into metastannic and antimonic acids. The fluid
is filtered, the insoluble residue well washed, and then boiled with
hydrochloric acid, which dissolves the metastannic and antimonic acids.
The solution is again filtered, and the second residue dissolved in
_aqua regia_. The metals dissolved in the several filtrates are then
detected, either by the processes previously given for the detection of
metallic poisons, or by the more complete methods contained in works on
chemical analysis. This qualitative test is, however, insufficient, in
case the falsification consisted in merely diminishing the proportions
of the valuable metals contained in the alloy, without changing its
qualitative composition: it is then necessary to execute a quantitative
estimation of the metals present. As this operation requires
considerable practice and the methods employed are to be found in all
treatises on quantitative analysis, we will not reproduce them here.
EXAMINATION OF ALIMENTARY AND PHARMACEUTICAL SUBSTANCES.
We will next enumerate the methods employed in the detection of the
principal adulterations to which flour, bread, oils of seeds, milk,
wines, vinegar and the sulphate of quinine are subjected. These
researches, united with those preceding, fail to embrace all the diverse
examinations which the chemical expert may be expected to execute; but
we do not claim to foresee all the contingencies that may arise, and
will describe the steps to be pursued in instances which are
anticipated, at the same time indicating general methods applicable to
cases not here included.
FLOUR AND BREAD.
The adulterations to which flour and bread are exposed usually consist
in adding damaged or an inferior grade of flour to wheaten flour, or in
disguising the presence of a poor quality of flour by the addition of
mineral substances, such as: plaster, chalk, lime, alum, and sulphate of
copper.
Good flour has a white color, possessing a slightly yellow tinge, but is
entirely free from red, grey or black specks. It is soft to the touch
and adheres to the fingers, acquiring, when compressed in the hand, a
soft cushion-like form. If mixed with water, it forms an elastic,
homogeneous, but slightly coherent dough, which can be extended out in
thin layers.
Flour of an inferior quality possess a dull white color, and does not
assume the cushion-like condition mentioned above, when pressed in the
hand, but escapes between the fingers: the dough formed is of a poorer
quality.
Flour which has been damaged by moisture has a dull or reddish-white
hue, and possesses a mouldy, or even a noxious, odor, as well as a
bitter and nauseous taste which produces a marked acid sensation in the
throat. Occasionally the presence of moisture causes the growth of
_fungi_, the introduction of which in the digestive organs would cause
serious results.
The constituents of pure flour are:
_Gluten._
_Starch_, in the proportion of 50 to 75 per cent.
_Dextrine_, in the proportion of several per cent.
_Glucose_, in the proportion of several per cent.
_Salts_, remaining in the ash obtained by the calcination of the flour,
in a proportion not exceeding 2 per cent.
_Water_, of which it loses 12 to 15 per cent., at the heat of a
water-bath, and 15 to 20 per cent., at a temperature of 160°.
_Bran_, (ligneous and fatty matter,) in a very small proportion, when
the flour has been properly bolted.
In the process of bread-making, the gluten undergoes fermentation by
the action of the leaven and liberates carbonic acid, which causes the
dough to become porous and swell up, or, as it is termed, to _rise_.
Bread contains the same substances as flour, but gluten and starch are
present in a state that does not admit of their separation by mechanical
means, and glucose, if present at all, exists in a smaller quantity: the
proportion of dextrine and water is, on the other hand, considerably
increased. The bread of the Paris city bakeries contains 40 per cent. of
water--the crumb, which forms 5/6 of the weight of the bread, containing
45 per cent.; the crust, which constitutes the remaining 1/6, containing
15 per cent. In army bread 43 per cent. of water are contained--the
crumb, which constitutes 4/5 of the weight of the bread, holding 50 per
cent.; the crust which forms the remaining 1/5, containing 15 per cent.
The addition of common salt naturally increases the proportion of ash
left upon calcining bread.
Water is contained in stale bread in the same quantity as in fresh
bread; but exists in a modified molecular condition: upon heating stale
bread, it acquires the properties of fresh bread.
The following substances are used in the adulteration of wheaten
flour:[P]
Potato-starch.
Meals of various grains (rice, barley, corn, oats and rye).
Vegetable meals, (beans, horse-beans, kidney-beans, peas, vetch,
lentils, etc.).
Darnel meal.
Buckwheat flour.
Linseed-meal.
Mineral substances (plaster, chalk, lime, alum, and sulphate of copper).
[P] Most of the substances here enumerated are rarely, if ever, used
for the adulteration of flour in this country. The analyst should,
however, give attention to the examination for such salts as alum,
sulphate of copper, plaster, kaolin, etc.--_Trans._
In order to detect these substances, the gluten, the starch, and the ash
are separately examined.
_a._ EXAMINATION OF THE GLUTEN.
In order to separate the gluten, two parts of the flour to be examined
and one part of water are mixed into a paste, and this is placed in a
fine linen sack, in which it is kneaded under a stream of water so long
as the washings have a turbid appearance: these are preserved. The
gluten obtained from good wheaten flour possesses a light-yellow color;
emits a stale odor; and spreads out, when placed in a saucer. In case
the flour has been too strongly heated in the grinding, or otherwise
badly prepared, the gluten is granulous, difficult to collect in the
hand, and somewhat resembles flint-stone in appearance.
Gluten prepared from a mixture of equal parts of wheat and _rye_ is
adhesive, blackish, without homogeneousness, spreads out more readily
than pure wheaten gluten, separates easily and adheres somewhat to the
fingers.
Gluten obtained from a mixture of wheat and _barley_ is non-adhesive, of
a dirty reddish-brown color, and appears to be formed of intertwined
vermicular filaments.
Gluten formed from a mixture of equal parts of wheat and _oats_ has a
blackish-yellow color and exhibits, at the surface, numerous small white
specks.
The gluten from a mixture of wheat and _corn_ has a yellowish color, is
non-adhesive, but firm, and does not readily spread.
Gluten prepared from a mixture of wheat and _leguminous flour_ is
neither cohesive nor elastic, and, if the proportion of the latter
present be considerable, can be separated and passed through a sieve,
like starch.
The gluten obtained from a mixture of equal parts of wheat and
_buckwheat_ flour is very homogeneous, and is as easily prepared as the
gluten from pure wheaten flour. It possesses when moist a dark-grey
color; which changes to a deep black upon drying. The proportion of
gluten in flour is exceedingly variable: good flour contains from 10 to
11 per cent. of dry gluten; poor flour from 8 to 9 per cent. of moist
gluten, equal to about one-third of its weight of the dry compound.
_b._ EXAMINATION OF THE STARCH.
The washings of the flour are allowed to stand for some time in a
conical-shaped vessel. As soon as the amylaceous matter has entirely
settled to the bottom of the vessel, the greater portion of the water is
decanted, and the residual mass brought upon a small filter and allowed
to dry. The residue is then examined for potato and rice starch.
_Potato starch._ The grains of potato starch are much larger than those
of wheaten starch. If a portion of the residue mentioned above is
crushed in an agate mortar, the granules of potato starch present are
ruptured, and their contents liberated; the wheaten starch remaining
unaltered. The mass is then taken up with water, and the fluid filtered.
If potato starch be present, the filtrate will acquire a blue color upon
addition of an aqueous solution of iodine; otherwise, a yellow or
violet-rose coloration is produced. It is necessary to avoid crushing
the residue for too long a time, as the granules of wheaten starch would
also become ruptured by prolonged comminution.
Besides the difference presented by potato starch in the size of the
granules in comparison to those of wheaten starch, the former swell to
ten or fifteen times the volume of the latter, when treated with a
solution of potassa: wheaten starch granules are not affected by the
treatment, if the solution used does not contain more than 2 per cent.
of the salt. The results obtained by the above operation should be
confirmed by a microscopic examination.
A portion of the residue is moistened with solution of iodine, then
carefully dried, and placed on the slide of a microscope. The mass is
next moistened with a solution containing 2 per cent. of potassa, and
examined. The addition of iodine causes the potato starch granules to
acquire a blue color, and renders their shape and volume more easily
perceptible; thus allowing the two varieties of starch to be readily
distinguished. Fig. 13 represents the relative size of the granules as
observed under the microscope.[Q]
[Q] It may be added, as a distinguishing property, that granules of
potato starch, when viewed in polarized light by aid of a Nicol's
prism, present a well-defined black cross, corresponding to the hilum;
wheaten-starch fails to exhibit this phenomenon.--_Trans._
[Illustration: Fig. 13.]
The presence of potato starch in bread is also detected by crushing a
small portion of the sample under examination on the glass, and then
adding a few drops of the alkaline solution.
_Rice and Corn._--If rice or corn meal have been mixed with the flour,
angular and translucent fragments (Fig. 14) are observed in the
microscopic examination. Corn meal acquires a yellow color, if treated
with dilute potassa solution.
[Illustration: Fig. 14.]
MISCELLANEOUS TESTS.