solution containing 14 per cent. of potassa and examined under the
microscope, numerous minute characteristic granules, smaller than the
grains of potato-starch, are observed. These possess a vitreous
appearance, sometimes a reddish color, and usually form in squares or
very regular rectangles. The test is equally applicable to bread. The
detection of linseed and rye meals is simultaneously effected by
exhausting the suspected flour with ether, then filtering the solution
and allowing it to evaporate. If the flour contains rye, the oil left by
the evaporation, when heated with a solution of mercury in concentrated
nitric acid, is converted into a solid substance having a fine red
color; but it remains unaltered, if entirely due to linseed. In case the
oil becomes solidified, the mercury salt present should be removed by
washing with water, the residue taken up with boiling alcohol of 36° B.
and the solution filtered: upon evaporating the alcoholic filtrate, a
residue is obtained consisting of the linseed oil present.
_Buckwheat._--Flour adulterated with buckwheat is less soft to the
touch, does not pack as easily, and passes more readily through a sieve
than pure wheaten flour. It presents, here and there, blackish
particles, due to the perisperm of the grain, and has a dirty-white
color. As previously remarked, the gluten obtained from a mixture of
buckwheat and wheaten flour possesses a grey or even a black color. The
starch furnished by buckwheat flour exhibits polyhedral agglomerations,
analogous to those presented by corn.
_Darnel._--The use of darnel in the adulteration of wheaten flour may
give rise to serious sanitary results. To effect its detection, the
flour to be examined is digested with alcohol of 35° B.: if the flour be
pure, the alcohol remains limpid: it acquires a straw-yellow tint, due
to traces of bran present, but--although a peculiar resin may be
dissolved--the solution does not possess a disagreeable taste. When, on
the contrary, darnel is present, the alcohol assumes a green tint, which
gradually deepens, and possesses a bitter and nauseous taste; the
residue, left by the evaporation of the tincture to dryness, has a
greenish-yellow color, and a still more disagreeable flavor than the
alcoholic solution.
_Legumens._--Leguminous meals cannot be added otherwise than in small
proportions to wheaten flour, owing to the rapidity with which they
change the properties of the latter, and communicate to it their
characteristic odor--noticeable upon treating the flour with a little
boiling water. Their presence is also easily detected by the distinctive
properties of the vegetable itself, and by the appearance of the
amylaceous residue in the microscopic examination. In order to decide as
to the presence of legumens, the washings containing the starchy matter
of the flour, after the particles of gluten present have been separated
by passing the fluid through a silk sieve, are divided into two
portions. One portion is allowed to undergo fermentation, at a
temperature of 18° to 20°: in case leguminous substances are not
present, lactic fermentation occurs and the odor of sour milk is alone
perceptible; if, on the other hand, legumens are contained in the fluid,
rancid fermentation takes place, and an odor is emitted resembling that
of decayed cheese. The remaining portion of the washings, after being
decanted from the residue of amylaceous matter, is filtered and
evaporated until a yellowish translucent pellicle appears upon its
surface. The fluid is then again filtered from the coagulated albumen
common to all flours, and the leguminous substances present coagulated
by the addition, drop by drop, of acetic acid.
The leguminous deposit produced appears white and flaky; when examined
under the microscope, it presents lamilla emarginated at the border; it
is odorless and tasteless; when dried, it assumes a horny appearance; it
is insoluble, both in water and alcohol, and does not become gelatinous
when treated with boiling water; it is readily soluble in potassa and
other alkaline solutions, from which it is precipitated upon addition of
nitric, hydrochloric, acetic, oxalic, and citric acids; upon protracted
boiling in water, it loses its property of being soluble in ammonia. The
above tests having been applied, the residue containing the starch is
next examined. For this purpose, a small portion is moistened with a
little water, a few drops of iodine solution added, and the mixture
placed on the side of the microscope: the bluish grains contained in the
polyhedral and cellular envelope (Fig. 15) are easily recognized. The
mixture on the glass may also be treated with an aqueous solution of
potassa (containing 10 per cent. of the salt), or with dilute
hydrochloric acid: these reagents dissolve the starch present, leaving
the reticulated tissue intact. Should this examination fail to give a
definite result, the remaining portion of the amylaceous residue is
subjected to a sort of levigation, and the part most slowly deposited
separated. In this portion the reticulated tissues of the leguminous
substances present are contained, and, as they are comparatively free
from foreign matters, their identification is a matter of comparative
ease. In case the presence of reticulated tissue is indicated, it is
still necessary to apply confirmatory chemical tests.
[Illustration: Fig. 15.]
Meals prepared from beans, horse-beans, and lentils, contain a tannin
which imparts a green or black color to salts of iron. The coloration is
rendered very sensitive if a rather considerable quantity of the flour
to be examined is passed through a silk sieve, and the remaining bran
treated with a solution of sulphate of iron (_ferrico-ferrous_
sulphate): the reaction immediately occurs, even if the sample contains
but 10 per cent. of bean meal. The meals of horse-beans and of vetches
acquire a red color, when exposed to the successive action of nitric
acid and of ammonia vapors. In order to apply this test, the suspected
flour is placed upon the edge of a capsule containing nitric acid, the
latter heated, and, as a yellow coloration appears, the acid removed and
replaced by ammonia. The capsule is then set aside: if the flour is
adulterated with either of the above vegetables, reddish spots, which
are easily perceptible by aid of a magnifying glass, are soon produced.
In case bread is to be examined, it is exhausted with water, the fluid
passed through a sieve, the upper layer decanted, then evaporated, and
the residue taken up with alcohol. The tincture so obtained is
evaporated, and the second residuum treated with nitric acid and
ammonia, as directed above. When meals prepared from beans, vetches, or
lentils are heated on a water-bath with hydrochloric acid, diluted with
three to four times its volume of water, a cellular tissue, possessing
the color of wine-dregs, remains behind; flours of wheat, peas, and
kidney-beans leave a colorless residue, when subjected to the same
treatment.
Finally; the grains of the starch (_fecula_) of legumens possess a
volume about equal to that of potato granules, and exhibit either a
longitudinal furrow in the direction of their longer axis, or a double
furrow arranged in a star-like form.
_c._ EXAMINATION OF THE ASH.
Leguminous substances, and more particularly mineral salts, are detected
by the examination of the ash left upon the incineration of the flour.
_Detection of Legumens._--Pure wheaten flour furnishes an ash consisting
of about 2 per cent. of its weight; whereas meals of legumens leave from
3 to 4 per cent. of their weight in ash. This difference is, however,
too slight to furnish conclusive results; the analysis of the ash is
also necessary. The ash of wheaten flour is non-deliquescent, dry,
semi-fused, and chiefly consists of phosphates of potassa, soda,
magnesia and lime, of sulphates, and of silica. The solution obtained by
treating the ash with water has an alkaline reaction. The phosphates of
the alkalies, present in the ash of wheat, exist in the state of
pyrophosphates, and, as chlorides are absent, the addition of nitrate of
silver to the aqueous solution of the ash produces a white precipitate,
consisting entirely of pyrophosphate of silver, which is not affected by
exposure to the light.
The ash of leguminous meals is deliquescent and soluble in water,
forming a _strongly_ alkaline solution, which contains both chlorides
and _neutral_ phosphates. The latter give a clear yellow precipitate
with nitrate of silver. Upon adding a solution of this salt to the
aqueous solution of the ash, a _pale_ yellow precipitate, which turns
violet if exposed to the light, is therefore produced.
_Detection of mineral substances._--The principal mineral substances,
that are fraudulently added to flour, are ground calcined bones, sand,
lime, plaster, alum, and sulphate of copper. The two last named salts
are almost invariably added in small quantities; alum renders the flour
white, even when used in the proportion of one per cent.; sulphate of
copper is added to impart a good appearance to bread made from a damaged
flour.
_a. Ground bones_ (carbonate and phosphate of lime).--The washings of
the gluten are placed in a conical vessel, and, after some time has
elapsed, the clear supernatant fluid is removed by means of a syphon, a
conical shaped deposit remaining on the bottom of the vessel: two hours
later, the fresh layer of fluid that has formed is removed with a
pipette. As soon as the residue becomes nearly solid, it is detached
from the vessel, placed upon a fragment of plaster, and allowed to dry.
The bones, being heavier than the amylaceous substances, are to be found
in the apex of the cone formed by the residue. This is detached, and
incinerated: in case the ash obtained contains phosphate and carbonate
of lime, the addition of hydrochloric acid will cause effervescence,
and, upon adding ammonia to the acid solution, a white precipitate will
be formed. If the solution is then filtered and oxalate of ammonia added
to the filtrate, a precipitate will be produced which, when heated to
redness, leaves a residue of caustic lime possessing an alkaline
reaction.
_b. Sand._--As this substance possesses a much greater specific gravity
than the usual constituents of flour, it is only necessary, in order to
accomplish its separation, to repeatedly stir the flour with water, and
remove the deposit at first formed, which, if consisting of sand, will
be insoluble in acids, and will grate, when placed between the teeth.
_c. Carbonates of lime and magnesia; vegetable ashes._--Carbonic acid
is always evolved, upon treating flour with hydrochloric acid. If the
base present be calcium, upon adding oxalate of ammonia to the filtered
solution--which has previously been neutralized with ammonia--a white
precipitate, possessing the properties mentioned above, will be formed;
in case the base is magnesia, the addition of oxalate of ammonia will
fail to cause a precipitate, but upon adding solution of phosphate of
ammonia to the fluid a granular precipitate of phosphate of ammonia and
magnesia is produced; if, finally, the flour contains vegetable
ashes--_i. e._ carbonates of the alkalies--bichloride of platinum will
produce in the acid solution a yellow precipitate: the addition of
vegetable ashes, moreover, would render the ash of the flour
deliquescent and very strongly alkaline.
_d. Lime._--In presence of lime, carbonic acid produces a white
precipitate, when conducted into the filtered aqueous extract of the
flour.
_e. Plaster._--The flour is boiled with water acidulated with
hydrochloric acid, the fluid filtered, and lime detected in the filtrate
by means of ammonia and oxalate of ammonia. The presence of sulphuric
acid is indicated by the formation of a precipitate insoluble in acids,
upon addition of solution of chloride of barium. Upon calcining the
flour without access of air, sulphate of lime is converted into the
corresponding sulphide: the residue of the calcination, when treated
with hydrochloric acid, evolves sulphuretted hydrogen, and the lime
present in the filtered acid solution is likewise precipitated by the
addition of ammonia and oxalate of ammonia.
_f. Alum._--A portion of the flour to be examined is treated with water,
the fluid filtered, and the filtrate divided in two portions: in one,
sulphuric acid is detected by means of chloride of barium; in the other,
alumina by adding a solution of potassa, which gives with its salts a
white gelatinous precipitate, soluble in an excess of the reagent.[R]
[R] If the detection of alum in bread is desired, a portion of the
crumb is incinerated in a platinum dish, the ash is treated with
concentrated hydrochloric acid, the filtered solution evaporated to
dryness, and the residue treated with hydrochloric acid, which now
leaves the silica present undissolved. The acid solution is then
filtered, nearly neutralized with carbonate of soda, and an alcoholic
solution of potassa added in excess. The earthy phosphates present are
now precipitated, alumina remaining in solution. The use of aqueous
potassa in this case--as well as in the case mentioned in the text--is
not advisable, as it is seldom entirely free from alumina. Upon
slightly acidulating the alkaline filtrate with hydrochloric acid, and
adding carbonate of ammonia, the alumina present is precipitated, and
may be dried and tested by means of the reaction with nitrate of
cobalt before the blow-pipe.
In the quantitative estimation of alumina, the phosphoric acid
usually present in the precipitate should be removed. This is done by
dissolving the precipitate in nitric acid and immersing a piece of
metallic tin in the boiling solution: phosphoric acid is thrown down
as a mixture of stannic oxide and phosphate, and the alumina is then
precipitated as usual by carbonate of ammonia.--_Trans._
_g. Sulphate of copper._--About 200 grammes of the bread under
examination are incinerated; the ash treated with nitric acid; the
mixture evaporated until it acquires a sticky consistence, and the mass
then taken up with water. The aqueous solution is next filtered; an
excess of ammonia and several drops of solution of carbonate of ammonia
added; the fluid again filtered, the filtrate slightly acidulated with
nitric acid, and divided into two parts. It is then ascertained if
sulphuretted hydrogen produces in one portion of the solution a brown
precipitate of sulphide of copper, and if solution of ferrocyanide of
potassium produces in the other a reddish-brown precipitate of
ferrocyanide of copper.[S]
[S] According to Wagner, if the ash, obtained by incinerating the
adulterated bread, is washed with water, shining spangles of metallic
copper are separated.--_Trans._
FIXED OILS.
Olive oil designed for table use is frequently adulterated with the oils
of poppy, sesamé, cotton-seed, pea-nuts, and other nuts; olive oil,
intended for manufacturing purposes, is often mixed with colza and nut
oils.
The tests used are of a rather unsatisfactory character. In all
instances, when the chemist is called upon to pronounce as to the
adulteration of an oil, it is necessary to execute comparative
experiments with the pure oil, and with admixtures arbitrarily prepared:
it is only when this is done that the indications obtained are of value.
EXAMINATION OF OLIVE OIL INTENDED FOR TABLE USE.
_a._ The density of the oil is determined by means of a hydrometer
(_oleometer_) provided with a scale giving the densities from 0.8 to
0.94, for the temperature of 15.° Pure olive oil possesses a specific
gravity of 0.917; poppy oil one of 0.925; a mixture of the two, an
intermediate density. Since the fixed oils are not definite chemical
compounds, this test is seldom conclusive.
_b._ Two or three cubic centimetres of concentrated nitric acid,
containing nitric peroxide in solution (or a solution of mercury in
strong nitric acid), are added to the oil to be examined, as well as to
a sample of pure olive oil. The two samples are then allowed to stand in
a room where the temperature does not exceed 10.° The _oleine_ of the
olive oil is converted into solid _elaidine_, and the mixture after some
time becomes sufficiently thick to remain in the vessel upon inversion.
If the sample under examination is free from adulteration, it will
solidify at the same time as the pure oil; whereas, the presence of one
per cent. of poppy oil, or of other drying oils, suffices to retard the
solidification for forty minutes.
_c._ Fifteen grammes of the oil are mixed in a glass vessel with the
same amount of strong sulphuric acid, the temperature of the two liquids
being previously observed. The mixture is stirred with a thermometer,
and the maximum temperature noted: pure olive oil produces an elevation
of temperature of 37.°7; pure poppy oil, an elevation of 70.°5; and a
mixture of the two an elevation of temperature intermediate between
37.°7 and 70.°5.
_d._ One volume of nitric acid of sp. gr. 1.33 is agitated with 5
grammes of the oil, and notice taken of the coloration produced after
the lapse of five minutes. If the olive oil is pure, it acquires a pale
green color; in case it is mixed with sesamé or nut oil, a deep-red
color appears: poppy oil also communicates a reddish coloration, but one
less deep than the preceding.
If an acid of sp. gr. 1.22 is taken, it is still less difficult to
distinguish between sesamé, nut and poppy oils; the latter assumes, in
this case, a pale yellowish-red color.
Pea-nut oil fails to exhibit a coloration; but can be recognized by its
conversion into a white solid, when mixed with 1/5 of its volume of a
solution of caustic soda of sp. gr. 1.34.
EXAMINATION OF OLIVE OIL INTENDED FOR MANUFACTURING PURPOSES.
The chief adulterations are colza and nut oils. The latter is detected
by means of the reaction with nitric acid, as described above. Colza oil
is recognized by mixing 5 volumes of the sample to be examined, with 1
volume of sulphuric acid of sp. gr. 1.655: if colza or nut oils are
present, a brown coloration ensues; under the same circumstances, pure
olive oil assumes a pale greenish hue. In case the sample acquires a
brown color when treated with sulphuric acid, and a red coloration is
produced by the addition of nitric acid, it contains nut oil; if
sulphuric acid produces a brown coloration, and nitric acid fails to
change it, the presence of oil of colza is indicated.
EXAMINATION OF HEMPSEED OIL.
This oil is frequently adulterated with linseed oil. The reactions
exhibited by these oils are nearly identical, and the detection of the
admixture is extremely difficult. It is advisable to mix the suspected
oil with sulphuric acid, notice being taken of the elevation of
temperature produced, and to treat it with nitric acid and with dilute
potassa solution, subjecting, at the same time, an artificial mixture of
the two pure oils to the same treatment, and comparing the results
obtained.
TEA AND ITS ADULTERATION.
Among alimentary substances probably no article is subjected to more
adulteration than tea. The sophistications practised may be conveniently
divided into three classes:
1. Additions made for the purpose of giving increased bulk and weight,
which include foreign leaves and exhausted tea-leaves, and also certain
mineral substances, such as metallic iron, sand, brick-dust, etc.
2. Substances added in order to produce an artificial appearance of
strength in the tea decoction, catechu, or other bodies rich in tannin,
and iron salts being chiefly resorted to for this purpose.
3. The imparting of a bright and shining appearance to the tea by means
of various coloring mixtures or "facings," which adulteration, while
sometimes practised upon black tea, is much more common with the green
variety. This sophistication involves the use of steatite (soap-stone),
sulphate of lime, China clay, Prussian blue, indigo, turmeric, and
graphite; chromate of lead and copper salts being but very rarely
employed. The compound most frequently used consists of a mixture of
soap-stone (or gypsum) with Prussian blue, to which a little turmeric is
sometimes added.
Genuine tea is the prepared leaf of _Thea sinensis_. It contains:
moisture, 6% to 10%; theine, 0.4% to 4.0%; tannin, (green) 20%, (black)
10%; ash, 5% to 6%; soluble extractive matters, 32% to 50%; and
insoluble leaf, 47% to 54%.
[Illustration: Fig. 16.]
[Illustration: Fig. 17.]
[Illustration: Fig. 18.]
[Illustration: Fig. 19.]
The presence of foreign leaves, and, in some instances, of mineral
adulterants, in tea is best detected by means of a microscopic
examination of the suspected sample. The genuine tea-leaf is
characterized by its peculiar serrations and venations. Its border
exhibits serrations which stop a little short of the stalk, while the
venations extend from the central rib, nearly parallel to one another,
but turn just before reaching the border of the leaf (see Fig. 16). The
Chinese are said to employ ash, plum, camellia, velonia, and dog-rose
leaves for admixture with tea, and the product is stated to be often
subjected in England to the addition of the leaves of willow, sloe,
beech, hawthorn, elm, box-poplar, horse-chestnut, and fancy oak (see
Figs. 17, 18, and 19). For scenting purposes chulan flowers, rose,
jasmine, and orange leaves are frequently employed. In the microscopic
examination the sample should be moistened with hot water, spread out
upon a glass plate, and then submitted to a careful inspection, especial
attention being given to the general outline of the leaf and its
serrations and venations. Most foreign leaves will, in this way, be
identified by their botanical character. The presence of exhausted
tea-leaves may also often be detected by their soft and disintegrated
appearance. If a considerable quantity of the tea be placed in a long
glass cylinder and agitated with water, the coloring and other abnormal
bodies present frequently become detached, and either rise to the
surface of the liquid as a sort of scum or fall to the bottom as a
deposit. In this way Prussian blue, indigo, soap-stone, gypsum, sand,
and turmeric can sometimes be separated and subsequently recognized by
their characteristic microscopic appearance. The separated substances
should also be chemically tested. Prussian blue is detected by heating
with a solution of caustic soda, filtering, and acidulating the filtrate
with acid, and then adding chloride of iron, when, in its presence, a
blue color will be produced. Indigo is best discovered by its appearance
under the microscope; it is not decolorized by caustic alkali, but it
dissolves in sulphuric acid to a blue liquid. Soap-stone, gypsum, sand,
metallic iron, etc., are identified by means of the usual chemical
tests. A compound, very aptly termed "Lie-tea," is often met with. It
forms little pellets consisting of tea-dust mixed with foreign leaves,
sand, etc., and held together by means of gum or starch. This, when
treated with boiling water, falls to powder. In the presence of catechu
the tea infusion usually becomes muddy upon cooling; in case iron salts
have been employed to deepen the color of the liquor, they can be
detected by treating the ground tea-leaves with acetic acid and testing
the solution with ferrocyanide of potassium. Tea should not turn black
upon immersion in hydrosulphuric acid water, nor should it impart a blue
color to ammonia solution. The infusion should be amber-colored, and not
become reddened by the addition of an acid.
TEA ASSAY.