ADULTERATION
AND
DETECTION.
--------------
The Teas of commerce are subject to four principal descriptions of
sophistication—“Facing” or Coloring with deleterious compounds, in order
to enhance their appearance;—Substituting with spent, partially-used or
exhausted leaves to increase their bulk and reduce the cost;—Mixing or
blending with spurious or foreign leaves, and—Sanding or adulterating
with a variety of mineral matter, chiefly iron or steel filings, to add
to the weight. Each trade has its own special form of adulteration, and
as in the milk business the most prevalent sophistications are watering
and skimming, so in the Tea-trade the besetting malpractice is coloring
and mixing with or substitution of partially-exhausted tea leaves, so
that the main efforts of experts and tea-analysts should be directed
more to this form of adulteration. The other forms have received some
attention from chemists and others interested in the article, but not to
the extent which the importance of the subject merits. But it is against
the two former most common and dangerous forms of adulteration that the
principal efforts of tea-analysts and inspectors should more
particularly be directed; and, while considerable of this nefarious and
positively injurious work is done in the countries of importation, by
far the greater portion is perpetrated in the countries of production.
For consummate skill in the “tricks of trade,” the Chinese as a people
have long been proverbial. “They are a self-ended people,” says an old
writer, “having the same reputation in Asia that the Jews have in
Europe.” Yet there are strong reasons for stating that many dealers in
our own and other tea-drinking countries have become expert imitators of
their methods, especially in the minor forms of coloring, mixing,
repacking and refacing. The sophistications in our own country being
chiefly confined to the admixture of damaged, stained and tainted teas
with sound, pure or high-grade goods, with the object of concealing or
disguising their defects, and the substitution of one variety for
another by repacking and relabeling. The latter form being practiced to
a much greater extent than most people imagine, giving rise to a special
branch of business in nearly all of the larger cities.
“FACED” OR COLORED TEAS.
Of the various forms of adulteration practiced in China and Japan
artificial coloring or “facing” is perhaps the most prevalent and
glaring. The material used for the purpose is usually composed of
Prussian blue, gypsum, indigo, turmeric, and more frequently, China
clay, a whitish iridescent powder, resembling mica, variously composed,
but generally consisting of _kaolin_ (soapstone), and sulphate of lime.
While that in use in Japan is not known, its composition being a secret,
known only to the manufacturers, but is evidently a preparation of
gypsum and kaolin, the Japanese contending that it is a vegetable
compound pure and simple. That kaolin is used in its preparation can
hardly be denied, as kaolin contains sulphur, and many of the lower
grades of Japan teas are found on infusion to possess a slightly
sulphurous odor. It has been proved, however, whatever its nature, to be
less harmful and injurious than the Chinese compound, and used only in
the manipulation and sophistication of the lower or commoner grades of
tea in that country.
The process of coloring or facing Green teas is performed by placing a
portion of Prussian blue in a porcelain bowl, not unlike a chemist’s
mortar, and pulverizing it into a fine powder, a small quantity of
gypsum being meanwhile burned over a charcoal fire, to soften it, after
which it is ground fine. The two substances are next mixed together, in
the proportions of one part blue to four parts gypsum, both making in
combination a light-blue preparation, in which state it is applied to
the leaves during the last process of firing, about five minutes prior
to removal from the pans, the time being regulated by a burning joss
stick. The Saihoo taking a handful of the compound, scatters it over the
leaves while in the pans, other operators tossing and turning the leaves
around rapidly with their hands meantime in order that it may equally
diffuse among them. One ounce of coloring-matter will face fifteen
pounds of leaves, imparting to them a dull leaden-blue hue, and “glossy”
or greasy appearance, readily detected in the hand. In many districts,
most notably in Ningpo and Canton, turmeric, kaolin, and China clay are
more extensively employed for the purpose. This almost transparent form
of adulteration is readily detected in the following manner:—
(1) When the tea is heavily coated it may be easily recognized by its
dull leaden-blue color and greasy appearance in the hand, or by placing
a small quantity of the leaves on a piece of glass or smooth table, on
removing them the coloring-matter will be found adhering to the hands,
glass or table, and its nature, whether Prussian blue, turmeric, kaolin
or indigo, readily determined with the aid of a microscope. (2) When
only lightly colored or suspected, place a sample of the leaves in a cup
or wine-glass and pour on briskly boiling water and stir well for two or
three minutes, then strain well through a thin muslin cloth. The
coloring-matter, if any, will be found adhering to the cloth, that
passing through, sticking to the sides, or forming a sediment at the
bottom of the vessel into which it is strained. If these deposits be
treated with a preparation of chlorine, or a solution of chloride of
lime, and turn white, the coloring substance used is indigo. But if
treated with a little potash, and it becomes brown, it will prove to be
Prussian blue, the application of a little sulphuric acid having the
effect of turning it blue again.
What are known to trade as “Canton Green teas” are made from tea-dust
and exhausted leaves ground up fine and aglutinized with a preparation
of gum, glue or other starchy substance to unite and hold them together
and then artificially colored or glazed. This fabrication is readily
detected by crushing the so-called leaves between the fingers or rubbing
them between the hands, upon which they leave a yellowish-brown stain,
greasy in nature. Or by powdering a small quantity of the alleged leaves
and treating the dust with a dilution of sulphuric acid it becomes very
much discolored, and if it assumes a leaden-blue color on the
application of caustic potash it is colored with Prussian blue. Again,
place a small quantity of the leaves in a cup or glass and pour on
boiling water, they will immediately begin to disintegrate and form a
thick, gluey deposit at the bottom of the vessel. By treating this
precipitate with a little iodine the mass will become separated and
dissolve into its original dust.
FOREIGN OR SPURIOUS LEAVES IN TEA.
Another reprehensible form of adulteration is the substitution or
admixture of foreign or spurious leaves obtained from other plants,
which resemble in structure but differ widely in character from the true
tea-leaf, such as those of the willow, plum or ash. Millions of pounds
of these leaves are annually picked, cured and colored in the same
manner as tea in China, and used for the purpose of increasing the bulk
and reducing the cost, while in England, particularly, the leaves of the
birch, elm, willow, chestnut, poplar and hawthorne have been extensively
used for the same purpose. The coloring material used in the latter
country differs from that used in China and Japan being still more
dangerous and injurious to health. This form of adulteration, however,
is trivial when compared with the former one, but, nevertheless, the
expert and analyst are frequently called upon to deal with it to a much
greater extent than most people imagine.
Such foreign leaves in tea may be best detected by their botanical
character or by the absence of the special structural marks which
distinguish the genuine tea-leaf from that of all other leaves in the
vegetable kingdom, for while the true leaf bears a strong resemblance to
that of the willow, ash and plum, it varies, however, in size form and
structure. The border of the true tea-leaf is more regularly serrated,
the serration stopping just short of the stalk, and the venations are
very characteristic, the veins running out from the mid-rib almost
parallel to one another, but altering their course before the border of
the leaf is reached, and turning so as to leave a bare space just within
the border of the leaf. So that in making an examination of a sample of
tea for the purpose of ascertaining whether these distinctive
characteristics are present in the leaves under treatment, it will be
found convenient to pour hot water on them so as to soften, uncurl and
spread them out more easily, as otherwise considerable difficulty will
be experienced owing to the brittleness of the tea-leaves in the dry
state.
TRUE TEA-LEAVES.
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[Illustration: CHINESE TEA-LEAF.]
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[Illustration: JAPANESE TEA-LEAF.]
The leaf of China Green tea is much broader than that of Black in
proportion to its length, but not so thick, and somewhat accuminate or
curled at the apex, that of Black being elliptical, oblong and flat in
shape, long and pointed, that of Green being much shorter and rounder in
form.
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[Illustration: INDIA TEA-LEAF.]
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[Illustration: CEYLON HYBRID TEA-LEAF.]
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[Illustration: JAVA TEA-LEAF.]
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[Illustration: SKELETON OF GENUINE TEA-LEAF.]
But in order to better detect the presence of spurious leaves in tea a
keener knowledge of the botanical formation of the true tea-leaf is
requisite, for which purpose the use of a microscope will be found an
invaluable aid. Tea-leaves in general construction bear a strong
resemblance to those of the willow and many other plants of the kind,
vary widely in size and form, being much smaller, more deeply serrated,
and ending more regularly just short of the stalk. The venations are
very characteristic, the veins running out from the middle rib, almost
parallel with each other, altering their course before reaching the
extremities, and turning so as to leave a bare space within the border.
When infused and unfolded it is of a bright-green color, the loopings
together of the principal veinings in the true leaf being very
characteristic. While the spurious leaf is either of a greenish-yellow
or reddish-brown color, and irregular in form under the same conditions
or when deprived of its cosmetics.
To still better distinguish between them treat a sample of the suspected
tea as in making an ordinary infusion to soften and expand the leaves,
then separate and uncurl them and lay flat on a piece of glass or other
smooth surface for comparison with the genuine leaf. Next see that they
agree in description and formation, but more especially in the venations
and serrations. Or soak the leaves in hot water, and carefully unroll
and closely examine their formation and structure and then compare
closely. The epidermis of the lower surface of the true leaf can be with
a little caution detached in small portions with a sharp razor, and then
analyze the frame or skeleton of the leaf in a little water or
glycerine, under a microscope, comparing the venations and serrations
with those of the genuine tea-leaf. Still another simple and inexpensive
test is to boil a few of the suspected leaves for a minute or two on a
watch glass, with a little distilled water, and add an equal portion of
burnt magnesia, treating the whole until it is reduced to a large-sized
drop. If no crystalline sublimate is obtained therefrom by the operation
the leaves cannot be those of genuine tea.
Chemically an examination of the ash of tea-leaves also affords some
criteria which may also be utilized for the purpose of identifying the
true tea-leaf. For instance, in common kinds of wood, such as oak, deal
and pine, the proportion of ash is a few-tenths per cent. of the whole,
and by taking wood in its ordinary air-dried condition it contains some
20 to 30 per cent. of moisture. Leaves, on the other hand, contain 10,
20 and even 30 times as much mineral matter, there being doubtless a
connection between this abundance of mineral matter and the active
chemical changes which take place in the leaves during the growth of the
plant. In tea-leaves, therefore, as in leaves in general, the ash
amounts to a considerable percentage, usually averaging about 6 per
cent., so that a chemical examination of the ash forms an important part
of the analysis of tea. The proportion of ash in all teas is tolerably
constant, genuine tea rarely yielding so little as 5 and never exceeding
6 per cent. of ash on incineration. Therefore, to determine the amount
of ash, weigh a small quantity of the tea in its ordinary commercial
state and burn it in a platinum crucible and then re-weigh the resultant
ash; by observing a few simple precautions very constant and accurate
results are attainable by this method. The crucible should be clean and
bright, the lid fitting precisely; an iron triangle, covered with a
tobacco pipe may be employed to support the crucible during ignition.
The operation is then commenced by igniting the empty crucible, and
allowing it to cool, being placed for that purpose on a piece of
porcelain or iron, immediately weighing the crucible on becoming cold.
Next place one or two grams of tea in the crucible, weighing both
together, and ignite over a spirit lamp or good gas-burner, stirring the
contents with a platinum wire for a few minutes. When ignition is
complete the crucible is covered with the lid, let cool again and
immediately weighed a second time. If there is any doubt as to the
completeness of the ignition, the crucible must be again ignited, and if
there is no difference in weight, the ignition is thereby proved
finished. As is obvious, in order to obtain accurate results it is
indispensable that the crucible should be in the same condition when it
is weighed empty and when weighed with the ash, and this is insured by
the preliminary ignition and rapid re-weighing, as above described.
The following determinations of the percentages of ash in spurious
leaves most used in the adulteration of tea, dried after the manner of
tea, may serve to illustrate, the leaves being gathered towards the end
of August:—
Kind of Leaf. Per cent. of Ash.
Ash, 9.40
Plum, 9.90
Willow, 9.34
To these may be appended the determinations of Paraguay tea at 28 and
the ordinary tea of commerce at 5.92 per cent.; while in Peligot’s
analysis the average proportions of ash in true tea-leaves is given as
follows:—
Kind of Leaf. Per cent. of Ash.
China Tea, 5.5
Japan “ 5.5
Java “ 5.3
India “ 6.06
Ceylon “ 6.06
Proving, as has been mentioned, that genuine tea-leaves as brought
direct from the producing countries, or such as is a fair commercial
article, does not yield less than 5, or sensibly more than 6 per cent.
of ash on incineration. When the ash much exceeds 6 per cent. the first
question to be considered is whether it is accidental or if the high
yield of ash would be maintained if a larger quantity of the sample were
incinerated. The composition of the ash of genuine tea-leaves has also
been carefully studied, yielding on analysis the following
constituents:—
Constituents. Per cent.
Soda, 0.65
Lime, 4.24
Potash, 39.22
Silica, 4.35
Chlorine, 0.81
Magnesia, 6.47
Oxide of iron, 4.38
Carbonic acid, 24.30
Sulphuric acid, A trace
Phosphoric acid, 14.55
Protoxide of manganese, 1.63
——————
Total, 100.00
This analysis is especially important, inasmuch as the tea which
furnished the ash was of guaranteed purity, so that no question of the
possibility of its sophistication could arise. On examining this
analysis it will be observed that tea-ash contains a quantity of iron,
also some manganese, the presence of manganese being so marked in
tea-ash that on subsequent treatment of the ash with water a deep-green
solution of manganate is obtained. Owing to this presence of manganese
in tea-ash it also invariably evolves chlorine very perceptibly when it
is treated with hydrochloric acid.
If the analysis of the tea-ash is referred to it will be noted that more
than one-half of it should be soluble in water, so that for all
practical purposes a complete analysis is not requisite, a determination
of the ratio of _soluble_ to _insoluble_ parts of the ash being
sufficient. Such a determination is made by boiling the ash several
times with a little water, filtering and washing the residue in the
filter, drying the precipitate, igniting and weighing it. The weight of
the insoluble part of the ash may then be subtracted from the weight of
the entire ash, in which manner both the percentage of the soluble and
insoluble ash will be conveniently arrived at, in which case the
following determination of the percentage of “soluble” and “insoluble
ash” in 100 parts of spurious leaves and pure tea when completely dried
will be of interest here:—
Kind of Leaf. Soluble Ash. Insoluble Ash.
Ash, 3.19 7.48
Plum, 5.66 4.24
Willow, 4.16 5.18
Teas of commerce, 3.55 2.47
Proving that in spurious leaves the ratio of soluble or insoluble ash is
very different from what it is in genuine tea-leaves, and that an ash of
such composition cannot be very soluble in water.
Peligot has also pointed out that tea leaves differ from other leaves by
their extraordinary richness in nitrogen, the prepared leaf being by the
process of curing rendered still more nitrogenous than the raw or spent
leaves, the former averaging, according to his experiments, 6 per cent.
of nitrogenous matter, and the latter 4.37, so that if the tea-leaf be
unique in containing such a high percentage of nitrogen, it is obvious
that a determination of nitrogen in tea may also be useful as a method
of identification.
The tea-extract also yields a comparatively large quantity of ammonia
when it is boiled with potash or permanganate of potash, and it is
probable that this characteristic may also prove very valuable in the
testing of tea. A solution containing about 10 per cent. of solid
potash, free from ammonia and nitrogenous matter is required for the
purpose, and easily obtained. So that a deficiency of theine, a
deficiency of nitrogen, and a deficiency of ammonia are all indicative
of the presence of foreign leaves in tea.
SPENT OR EXHAUSTED LEAVES IN TEA
Are principally used in the adulteration of Black teas, and is effected
by adding or substituting leaves that have been at least once used, and
from which all the vital properties have been extracted. The Chinese
being inveterate tea-drinkers, large quantities of these leaves are
always to be had for the purpose, they are re-dried and subjected to a
treatment of gypsum or terra-japonica, in order to make them retain
their curl, and then glazed or “faced” with a preparation composed of
either graphite or silica to enhance their appearance in the hand; a
decoction obtained from catechu or logwood being next added to impart a
tea-like color to the liquor when infused. This vile compound is known
to the Chinese as “Bastard tea,” and is rarely sold alone, being used
principally for mixing or blending with pure teas.
The presence of spent or exhausted leaves in either Green or Black tea
is best determined by estimating the amount of tannin contained in the
liquor after infusion, and for which experiment various tests are in
use. A large proportion of the tea-extract is found to consist of tannin
(tannic acid), there being much more in Green than in Black tea, the
larger portion of that originally existing in the latter being
dissipated by the extra fermentation to which this variety is subjected
in curing and firing. Green teas contain on an average about 15 per
cent. of tannin, Black teas never exceeding 10 per cent. This rate,
however, varies considerably from different causes, such as age,
quality, soil and climatic condition of the districts of growth, the
main average being 12 and 9 per cent. respectively in pure teas. Spent
or exhausted leaves, on the other hand, contain only 2 per cent. on an
average at the highest estimate, a difference of 7 to 10 per cent. of
tannin, as will be observed, in favor of pure teas.
For the purpose of estimating the percentage of tannin contained in tea,
the simplest method is to make an infusion of the leaves and pour it
into a cup or glass and add to it a small quantity of a standard
solution of plumbic acetate. The acetate will cause the tannin to form a
precipitate, which must be removed and weighed in a small scale fitted
for the purpose; then by taking the nominal percentage of tannin
contained in pure teas at 12 in Green and 10 in Black and 2 per cent. in
Spent or exhausted leaves, the difference will be the percentage of
adulteration, the extent being indicated by the lessened proportion of
tannin in the same ratio. The presence of Catechu (soluble salts of
iron) is best ascertained by making an ordinary infusion of the leaves,
allowing the liquor to cool and pouring it into a cup or glass. Next add
a preparation of neutral plumbic acid and separate the precipitate
formed by the introduction of the chemical by filtration, and adding a
little argentic nitrate to the filtrate. If catechu be present the
residue will turn a dark-brown, the liquid meanwhile acquiring a deep
yellow hue, while under the same conditions the liquor of pure tea will
remain unaffected. But if the cosmetic be extensively employed, a weak
solution of ferric-chloride will cause the precipitate to turn
light-green or it may be detected under the microscope if heavily
coated.
Spent and spurious leaves may also be readily detected by the “ash
test,” through the following deductions: Pure teas, as shown above,
contain from 5 to 6 per cent. of ash on incineration, 2 per cent. of
this being soluble in boiling water; any increase of these parts is a
certain indication of the presence of foreign or exhausted leaves in the
sample treated. The percentage of ash contained in spent leaves, ranging
from 10 to 30, and in spurious leaves from 40 to 50, in many instances,
while the residue of teas adulterated with mineral matter have been
known to reach as high as 75 to 80 per cent. of the incinerated sample.
The presence of logwood is best exposed by the addition of a few drops
of sulphuric acid to an infusion made with the leaves in the ordinary
way. If any of the dye be present this acid will cause the liquid to
turn a deep red, but if the tea be uncolored the liquor will remain
entirely unaffected. Graphite being visible to the naked eye is easily
distinguished by its characteristic glossy nature, or can be separated
by treating the leaves with boiling water in the usual manner and
evaporating the infusion. The substance, if present, will form a deposit
at the bottom of the vessel or will be found adhering to its sides if
used in large quantities. While Silica is readily recognized by the
increased amount of ash insoluble in the water obtained by calcimining a
sample of the tea so adulterated, as above described.
SAND AND MINERAL MATTER IN TEAS
Is frequently introduced into tea with the object of adding weight, and
is best detected by the “ash-test.” As formerly stated, the leaves of
genuine tea, or tea of fair commercial value, yield from 5 to 6 per
cent. of ash or mineral matter on incineration, 2 per cent. of which is
again soluble in water. This rate is fairly constant, and ranges from 5
in Black teas to 6 per cent. in pure Green, rarely yielding as low as 5
in the former and never exceeding 6 in the latter, while many of the
teas of commerce are found to yield from 13 to 20 per cent. of ash on
incineration. Such teas are unmistakably sophisticated, and will be
found, on analysis, to contain sand or other mineral matter in their
composition.
To determine the amount of mineral matter contained in teas so
adulterated, proceed as in the case of spurious and spent leaves, which
analysis may be again confirmed by a determination of the ratio of
soluble to insoluble matter contained in the ash. The result is obtained
by boiling the ash in a little water and filtering the precipitate,
drying, burning, weighing and subtracting the residue or insoluble
matter from the original weight of the ash. By this process both the
soluble and insoluble parts are ascertained, and if the sample be pure,
but 3 to 3½ per cent. of insoluble will remain, any increase of these
figures clearly denoting adulteration to that extent.
Where the burning of the leaves is inconvenient, the following operation
may be substituted: Weigh a sample of the suspected tea and boil with
about ten times its weight of water in a porcelain dish or beaker. This
boiling will wash the sand off the leaves and sink to the bottom, the
leaves floating in the liquid. When the liquid has cooled sufficiently,
the leaves may be removed with the hand, the liquid and sand being
poured into a filter. The sand is then washed, dried and ignited in a
platinum plate and weighed, in which manner the amount of sand yielded
by 50 or 100 grams of tea may be actually weighed and ascertained. On
examining the analysis it will be found that tea-ash contains a quantity
of iron and some manganese, the presence of the latter being so marked
in tea-ash, that on subsequent treatment of the ash with water a deep
green solution of the manganate is obtained. Owing to the presence of
this chemical, tea-ash also evolves chlorine very perceptibly,
particularly when treated with hydrochloric acid. If the sample of tea
treated yield _only_ the normal percentage of ash at the same time
contains a considerable quantity of silica, such a combination would
afford the strongest evidence of adulteration. This will be apparent
from the fact that tea-ash is an essential part of the tea, and if a
part of the tea-ash be absent, the sample must have been deprived of at
least the corresponding quantity of tea. Spent leaves contain less ash
than genuine tea, the average being about 3.06 of ash in 100 parts of
dried spent leaves, and when the ash is deficient, the explanation is
that the genuine tea has been more or less replaced by spent or
exhausted leaves. But for all practical purposes a complete analysis of
tea-ash is not necessary, a determination of the ratio of soluble to
insoluble portions of the ash answering the purpose as well. Such a
determination is made by boiling the ash several times with a little
water, filtering and washing the precipitate in the filter, drying,
igniting and weighing it. The weight of the insoluble part of the ash
may then be subtracted from the original quantity, in which manner the
percentage of soluble and insoluble ash is obtained.
Peligot has also pointed out that tea-leaves differ from the leaves of
other plants by their extraordinary richness in nitrogen, the percentage
averaging 4.37 per cent. in the raw leaf of the former, and ranging from
5.10 to 6.60 per cent. in the dried state. In the preparation of the
fresh leaves for market a quantity of juice is expressed from them, the
increase of nitrogen in the prepared leaf being accounted for on the
supposition that this juice is not as rich in nitrogen as that still
remaining in the leaf, and if the prepared leaf be unique in containing
this high percentage of nitrogen, it is obvious that a determination of
nitrogen in tea may prove useful as a method of identification.
IRON AND STEEL FILINGS IN TEA
Are best detected by pulverizing a sample of the suspected tea and
spreading the powder on a piece of glass or plate, and applying a magnet
to the dust. If a quantity of the particles gravitate and adhere to it,
the tea is undoubtedly adulterated in this form. While fabrications and
sophistications in general may be best exposed by treating an infusion
of the leaves with a watery solution of sulphuretted hydrogen or a weak
solution of ammonia. Under the first treatment the liquor of pure teas
will retain its natural color, but will assume a light-blue tint under
the latter.
Another simpler method for those who may not have the chemicals or
appliances convenient is to place a small quantity of tea-leaves in a
wine-glass or goblet, pour on cold water, and stir or shake well for a
few minutes. The tea, if pure, will only slightly color the water, but
if adulterated, a dark-colored liquor is quickly yielded, which if
boiled and let stand until cold will, if spurious, become bitter and
almost transparent as it cools, while pure tea under the same conditions
assumes a darker color and pleasing flavor. The latter changes arise
from the tannin (a natural property in tea) of which artificial tea is
entirely devoid and adulterated teas in proportion. Mineral adulterants,
however, must be dealt with by the ash-test, which is unerring, spurious
leaves by their botanical character and structural marks, deficiency of
tannin being invariably an indication of spent or exhausted leaves.
The part of the tea which we really use being that which passes into the
infusion, in other words—the Extract of tea—it is natural to look to
this extract as affording the directest evidence of the quality and
genuineness of a sample of tea. The extract may be regarded both
quantitatively and qualitatively, and from the former point of view we
are led to the tea-assay or determination of the weight of the
tea-extract which a given weight of tea is capable of yielding.
In Peligot’s analyses we find the following determinations of the
tea-extract—the author being quite alive to the importance of such a
test:—
GREEN TEAS.
Part soluble in boiling water.
┌─────────────┴─────────────┐
Variety. Dried Leaf. Ordinary Conditions.
Imperial, 43.1 39.6
Gunpowder, 50.2 49.9
BLACK TEAS.
China, 42.8 39.0
Japan, 45.8 41.5
India, 45.4 41.7
Java, 35.2 32.7
Ceylon, 44.4 39.8
These results being arrived at by the employment of a valid but rather
inconvenient method of weighing out ten grams of tea-leaves and boiling
them with water as long as anything is dissolved out of them, and
afterwards drying up the exhausted leaves, first at a low temperature
and then at a higher one, finally weighing the exhausted leaves. The
loss in weight is the weight of the tea-extract, care being taken to
weigh the original tea and the exhausted tea-leaves in the same state of
dryness. The results, as will be observed, are stated both in the dried
tea and in the tea in its ordinary commercial condition. But, instead of
weighing the tea-leaves before and after extraction and taking the
difference in weight as the weight of the extract there is a more
convenient process—that of evaporating down the extract itself to
dryness and weighing _it_. The drying up of the exhausted leaves and the
getting them into the same hygroscopic condition as the original tea
presenting considerable practical difficulties.
The evaporation of the infusion to dryness and the weighing of the dry
extract is also a tedious process in its unmodified state. But if a
given quantity of tea be boiled with successive portions of water no
more tea-extract is yielded than if the same tea be boiled once with a
large quantity of water, but whether the infusion is kept for a length
of time just at the boiling-point or whether it be made to boil
vigorously makes some difference in the result, brisk-boiling extracting
about one-tenth more than slow boiling, so that if the boiling be very
vigorous half an hour’s boiling is just as effective as an hour’s slow
boiling.
Founded on these observations an assay of the tea-extract may be made by
the following simple process: Put ten grams of tea into a pint flask and
pour on about two-thirds of distilled water accurately measured, a cork
and bent tube is then adapted to the mouth of the flask and a connection
made with a condenser. The contents of the flask are next heated and
made to boil strongly. That having been done the boiling is stopped and
the flask and condenser disconnected and the distillate poured back into
the flask and the decoction of tea observed closely. If quite clear
fifty grams are weighed out and evaporated to dryness in a water-bath
and weighed till constant. If the decoction be not quite clear by this
time it is to be filtered hot; the first small filtrate is best thrown
away and the filtrate collected, weighed, and dried in the water-bath
until the residual tea-extract becomes quite constant. Having performed
the operation in the manner directed, the weight of the tea-extract
actually weighed will be the weight of the extract yielded by one gram
of the sample to be assayed.
But in coming to a decision as to the genuineness of a sample of tea of
which an analysis has been made by this method, it is of importance to
remember that genuine tea is subject to considerable variation in
composition. The quality and condition of the leaf at the time of
gathering and the different treatments which it undergoes in the process
of manufacture, or whether the tea is Black or Green, cause the
composition to exhibit a wide range of variation. Taking the percentage
of the extract as a basis from which to start, that in genuine tea being
from 32 up to 50 per cent. in its ordinary commercial condition. Such
being the case, it is obvious that a determination of the percentage of
extract will not enable the expert or analyst to say whether the sample
of tea be of a lower or higher grade of pure tea, or whether it is
composed of a high grade of genuine tea and a portion of exhausted
leaves. In a general way, however, this question is not of vital
importance to the analyst, as a solution may be arrived at from a
determination of the soluble ash, which would be found rather deficient
on incineration. For although tea may be exceptionally rich in extract,
and although there are difficulties in the way of deciding whether a
given sample of tea consists of average quality or of fine tea mixed
with spent tea, there are no such difficulties in recognizing the case
of tea of average grade, mixed with a considerable quantity of exhausted
leaves, as it is assumed in this formula that the soluble ash in genuine
tea is 3.6 per cent. and that in spent tea only 0.3 per cent. But in
using this formula it must be understood that the results are only rough
approximations, judgment and discrimination being required to determine
by it.
Tea-extract yields a comparatively large quantity of ammonia when it is
boiled with potash and permanganate of potash, and it is probable that
this character may prove very valuable also in testing the purity of
tea, for which purpose a solution containing about 10 per cent. of solid
potash, free from ammonia and nitrogenous matter, is required and easily
obtained. Ten grams of this solution of potash is put into a small
flask-retort, working in an oil-bath and connected with a small
condenser; the whole apparatus to be carefully freed from the last
traces of ammonia, which is best accomplished by distilling the water
through it, after which from 5 to 10 parts of the tea infusion are
poured into the retort, which is then corked up and heated in an
oil-bath to 150 C. Having been maintained for a short time at this
temperature it is then lifted out of the bath and some pure water poured
into the retort, which is again to be heated in the oil-bath. More than
half of the water is then distilled over and in this manner the “free
ammonia” is obtained from the distillate. When this has been
accomplished some of the potash and permanganate solution is added to
the contents of the retort and distilled so as to yield a distillate
containing “albuminoid ammonia,” the result being as follows in pure
teas:—
Free ammonia, 0.28 milligrams.
Albuminoid ammonia, 0.43 “
—————
Total, 0.71 milligrams.
While the extract from a sample of spurious leaves yielded of
Free ammonia, 0.20 milligrams.
Albuminoid ammonia, 0.295 “
—————
Total, 0.495 milligrams.
This experiment is made with the greatest ease, and will also be found
valuable by brokers and others interested in tea for testing the
strength of the tea-infusion. As has already been observed, tea is also
remarkably rich in nitrogen, so much so that a determination of nitrogen
may be resorted to as a means of identification. With this object it is
best to take a sample of tea, first mixing it up well and powder it in a
mortar. Of this tea-powder some 0.3 grams should be accurately weighed
out. This is then to be mixed with some 50 grams of oxide of copper,
which has been first oxidized without the employment of nitric acid, and
which shortly before using had been ignited and allowed to cool. A
combustion-tube of hard German glass, closed at one end and perfectly
clean, is next charged as follows: At the closed end a layer, some three
to four inches in length, of a mixture of dry bi-carbonate of soda and
fused bi-chromate of potash is placed, the mixture being intended to
give out carbonic acid. Next to this compound place two inches of oxide
of copper, then the mixture of tea and oxide of copper, then more oxide
of copper and some clean metallic copper on top, then a perforated cork
and exit tube, which dips under the mercury, and place the
combustion-tube in an appropriate furnace to heat. By heating the layer
of carbonate of soda and bi-chromate of potash, carbonic acid is caused
to traverse the tube and expel the air from it. This having been done
the tube is next heated gradually from before so as to burn up the tea,
the gases being collected over the mercury. At the end of the operation
the carbonic acid is once more made to traverse the tube by again
heating the mixture at the back, all the nitrogen being driven from the
tube and collected. Finally the carbonic acid is absorbed by means of
the potash and, the residual nitrogen gas is measured with well-known
precautions. This gas should also be tested for bin-oxide of nitrogen by
means of oxygen and pyro-galate of potash, any bin-oxide of nitrogen gas
to be measured and allowed for in the test.
Among the most common forms of adulteration practiced by dealers in this
country is that of substituting old and valueless Young Hysons for
Japans or mixing them together the better to disguise the fraud. The
mixing or blending of old, stale, weedy or smoky Congous with Oolongs,
particularly when such teas become a drug on the market. The reduction
of Moyunes by the addition of Pingsueys in the proportions of half and
half and then refacing them as “True Moyunes.” The refacing of Ningyongs
and other Amoys as Formosas being still another form, for which at the
present low prices of the commodity there is not the slightest occasion.
The most recent “trick” of the tea trade being that of mixing Japan Nibs
with Twankays and Hysons, the latter, I regret to add, being now
extensively adopted by at one time reputable houses.
Some law should be passed in this country to ensure the public against
the possibility of purchasing spurious and adulterated teas as in
Russia, where the dealers are compelled to sell their teas under
government labels placed on the packages by experts appointed by the
Government for that particular purpose and who work under official
inspectors, the expense of examining and labeling being defrayed out of
the revenue realized from the sale of the labels to the dealers. To such
an extent was the nefarious practice carried on in that country that the
adoption of this system became imperative in order to restore the
confidence of the public in the genuineness of the tea offered for sale,
with the result of having materially checked the traffic in spurious and
adulterated teas in that country.
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