included. The processes suggested for this determination are rather
unsatisfactory; and there appears, moreover, to exist no direct relation
between the quality of tea and the proportion of theine contained. The
tests here mentioned, in connection with those already given, will, it
is believed, usually suffice to indicate to the analyst the presence of
spent leaves, inorganic coloring matters, and other mineral
adulterations.
TANNIN.--A good process for the estimation of tannin in tea has been
published by Allen (_Chem. News_, vol. xxix. p. 169 et seq.) A standard
solution of lead acetate is prepared by dissolving 5 grammes of the salt
in distilled water and diluting the liquid to 1,000 c.c. As an
indicator, 5 milligrammes of potassic ferricyanide are dissolved in 5
c.c. of water, and an equal volume of strong ammonia-water added. The
exact strength of the lead solution is to be determined by means of a
solution of pure tannin of known strength. Two grammes of the tea to be
tested are powdered, boiled with water, and, after filtering and
thorough washing, the decoction is made up to a volume of 250 c.c.; 10
c.c. of the lead solution are now diluted with 90 c.c. of boiling water,
and the tea infusion is gradually added from a burette until a few drops
of the liquid, when filtered and added to a little of the indicator
placed upon a porcelain slab, causes a pink coloration to appear; 125,
divided by the number of c.c. of tea infusion found to be necessary to
produce the pink color, will give directly the percentage of tannin in
the sample examined. As previously stated, green tea contains 20% of
tannin, and black tea 10%. In spent tea, however, only about 2% of
tannin is present; and, although any tea deficient in this constituent
could be fortified by the addition of catechu, its determination often
affords indications of value.
THE ASH--_a. Total Ash._--5 grammes of the sample are placed in a
platinum vessel and heated over a Bunsen burner until complete
incineration has been accomplished. The vessel is allowed to cool in a
desiccator, and is then weighed as quickly as possible. In genuine tea
the total ash should not be much below 5% or much above 6%, and it
should not be magnetic; in "faced" teas the proportion of total ash is
often 10% or 15%; in "lie-tea" it may reach 30%, and in spent leaves it
may fall as low as 3%, the ash in this case being abnormally rich in
lime salts and poor in potash salts. Tea-dust sometimes contains 10% of
total ash without necessarily being considered bad in quality. In the
proposed United States tea-adulteration law (1884) a maximum of 8% of
total ash is allowed for tea-leaf.
_b. Ash insoluble in water._--The total ash obtained in _a_ is washed
into a beaker and boiled with water for a considerable time. It is then
brought upon a filter and the insoluble residue washed, dried, ignited,
and weighed. In unadulterated tea it will not exceed 3% of the sample
taken.
_c. Ash soluble in water._--This proportion is obtained by deducting ash
insoluble in water from the total ash. Genuine tea contains from 3% to
3.5% of soluble ash, or at least 50% of the total ash, whereas in spent
or exhausted tea the amount is often but 0.5%.
_d. Ash insoluble in acid._--The ash insoluble in water is boiled with
dilute hydrochloric acid and the residue separated by filtration,
washed, ignited, and weighed. In pure tea the remaining ash ranges
between 0.3% and 0.8%; in "faced" teas, or in teas adulterated by the
addition of sand, etc., it may reach the proportion of 2% to 5%.
Fragments of silica and brick-dust are occasionally to be found in the
ash insoluble in acid.
THE EXTRACT.--Two grammes of the carefully-sampled tea are boiled with
water until all soluble matter is dissolved, water being added from time
to time to prevent the solution becoming too concentrated. The solution
is poured upon a tared filter, and the remaining insoluble leaf
repeatedly washed with hot water until the filtered liquid becomes
colorless. The filtrate is now diluted to a volume of 200 c.c., and of
this 50 c.c. are taken and evaporated in a weighed dish over the
steam-bath until the weight of the extract remains constant; its weight
is then determined. Genuine tea affords from 32% to 50% of extract,
according to its age and quality; in spent tea the proportion of extract
will be greatly reduced.
INSOLUBLE LEAF.--The insoluble leaf obtained in the preceding operation,
together with the weighed filter, is placed in an air-bath and dried for
at least eight hours at a temperature of 110° C.; its weight is then
determined. In unadulterated tea the amount of insoluble leaf ranges
between 47% and 54%; in exhausted tea it may reach a proportion of 75%.
It should be noted that in the foregoing estimations the tea is taken in
its ordinary air-dried condition. If it be desired to reduce the results
obtained to a dry basis, an allowance for the moisture present in the
sample (an average of 8%), or a direct determination of the same, must
be made.
The following tabulation gives the constituents of genuine tea so far as
the ash, extract, and insoluble leaf are involved:
_Total ash_--ranges between 4.7% and 6.2%.
_Ash soluble in water_--ranges between 3% and 3.5%; should equal 50% of
total ash.
_Ash insoluble in water_--not over 2.75%.
_Ash insoluble in acid_--ranges between 0.3% and 0.8%.
_Extract_--ranges between 32% and 48%.
_Insoluble leaf_--ranges between 43% and 58%.
The table below may prove useful as indicating the requirements to be
exacted when the chemist is asked to give an opinion concerning the
presence of facing admixtures or of exhausted or foreign leaves in a
sample of tea:
_Total ash_--should not be under 4.5% or over 7%.
_Ash soluble in water_--should not be under 40% of total ash.
_Ash insoluble in water_--should not be over 3%.
_Ash insoluble in acid_--should not be over 1%.
_Extract_--should not be under 30%.
_Insoluble leaf_--should not be over 60%.
NOTE.--The British Society of Public Analysts adopt:
_Total Ash_ (dry basis)--not over 8% (at least 3% should be soluble in
water).
_Extract_ (tea as sold)--not under 30%.
MILK.
The chief constituents of milk are water, butter, caseine, lactose
(milk-sugar), traces of albumen and mineral salts. Butter is present in
the form of minute globules, held in suspension; the caseine, for the
greater part, is in solution, only a small portion being present in an
insoluble suspended condition. In milk only a few days old, the
_colostrum_ (the milk secreted during the first few days after
parturition) consists largely of rather voluminous cellular
conglomerations, containing a sufficient quantity of albumen to
coagulate upon heating.
The normal density of milk is 1.030, water being 1.000; the density
rising to 1.036, if the fluid has been skimmed.
Good milk contains, on an average, 3.7 per cent. of butter; 5.7 per
cent. of lactose, and leaves upon evaporation 12 to 14 per cent. of
solid matters.[T] The most common adulteration of milk consists in the
addition of water. This fraud is detected by means of an areometer
(_lactodensimeter_) which gives directly the specific gravity of the
fluid under examination. Should the density be much below 1.030, it is
certain that water has been added. It does not, however, necessarily
follow if it is about 1.030 that the milk is pure, since the gravity of
the fluid, which would be increased upon skimming, could be subsequently
reduced to 1.030 by the addition of water. The lactodensimeter,
therefore, although useful in the detection of a simple admixture, fails
to give reliable results if the fraud perpetrated is a double one; and a
determination of the proportion of butter present is also usually
necessary. Numerous methods have been proposed to accomplish this
estimation. The most preferable of these, owing to the rapidity with
which the operation is executed, is the use of the lactoscope
(_galactoscope_). This instrument consists of a tube provided with a
glass plate fitted at one end, and with a movable glass plate at the
other extremity. A few drops of the milk to be tested are placed between
the two plates, and the tube lengthened, by screwing out the movable
plate, until the fluid no longer transmits the light of a candle placed
at a distance of one metre. As the opacity of milk is due to the butter
present, it is evident that the proportion of this substance contained
in the sample can be estimated by the relative distance which the plates
have been separated.
[T] The British Society of Public Analysts regard the following as the
_minimum_ proportions of constituents in unadulterated milk:
Fat 2.5 per cent.
Solids, not fat 9. " "
----
Total 11.5 " "
Water 88.5 " "
--_Trans._
The lactoscope possesses, however, but a limited degree of precision.
_M. Marchand_ substitutes to its use the following tests: A test-tube is
graduated in three equal divisions, the upper one being subdivided into
hundredths extending above, in order to determine accurately the correct
volume of the fluid, expanded, as it is, by the temperature of 40°, at
which the examination is executed. The first division of the tube is
filled with milk, a drop, or two of strong potassa lye added, and the
mixture well shaken: the second portion is then filled with ether, and
the third with alcohol. The mixture is next again thoroughly agitated,
and then exposed to a temperature of 40° in a water-bath. After standing
for several hours, a layer of fatty matter becomes sufficiently
separated to allow of measurement: but, as it contains some ether and as
a small amount of butter may still be retained in the lower aqueous
fluid, a correction of the results obtained is necessary. M. Marchand
has compiled a table, which facilitates this correction (_vide_: _Journ.
de Pharm., Novembre 1854_, and _Bulletin de l'Académie de Médecine,
Paris, 1854_, xix., p. 1101).
Previously to the introduction of Marchand's apparatus, use was made of
the _lactometer_, which consists simply of a graduated glass tube, in
which the suspected milk is allowed to remain for 24 hours, at a
temperature of 15°. After the lapse of this time, the cream present
completely separates as a supernatant layer, the thickness of which
indicates the quality of the sample taken.
_M. Lacomte_ recommends the addition of glacial acetic acid, in order to
cause the more rapid separation of the cream.
The estimation of the butter being accomplished, it is frequently
needful to determine the amount of lactose present. For this purpose,
recourse is had to Barreswil's method, based upon the reduction of
cupro-potassic tartrate by milk-sugar in the presence of alkalies. A
solution is prepared containing 40 grammes of pure crystallized sulphate
of copper, 600 or 700 grammes of caustic soda lye of sp. gr. 1.12, and
160 grammes of neutral tartrate of potassa. The sulphate of copper and
tartrate of potassa are previously dissolved separately in a little
water, the three solutions united, and water added until the fluid
acquires a volume of 1154.4 cubic centimetres. In order to standardize
this test solution, a known weight of pure lactose is dissolved in water
and the fluid added, drop by drop, from a graduated burette, to a small
flask containing 10 cubic centimetres of the copper solution, diluted
with 40 cubic centimetres of distilled water, and heated to boiling. At
first a yellow precipitate forms, which gradually turns red, and is
deposited on the bottom of the flask, leaving the solution colorless. As
soon as the test solution is completely decolorized, the addition of the
lactose solution is discontinued, and the weight of lactose
corresponding to 10 cubic centimetres of the test fluid calculated from
the quantity used. The standard of the test solution having been
determined, the above operation is repeated, the milk under examination
being substituted for the solution of pure lactose. The quantity of milk
necessary to decolorize 10 cubic centimetres of the copper solution will
evidently contain the same amount of lactose as the quantity of solution
used in the preliminary test, and the actual amount of lactose present
is very easily calculated. When an estimation of the solid matter
contained in the milk is required, a known weight is evaporated to
dryness over a water-bath, and the residue weighed. In performing this
evaporation, the addition of a known amount of sand, or ground glass, is
advisable. The amount of ash present is determined by incinerating the
residue left by the evaporation.
Foreign substances are sometimes added to milk, for the purpose of
disguising the presence of an abnormal quantity of water, the principal
of which are: chalk, bicarbonate of soda, emulsion of almonds, gum
tragacanth, gum arabic, starch, flour, decoction of barley or rice,
sugar, and cerebral substances. These bodies are detected as follows:
_Chalk._--If chalk is contained in the milk, it readily subsides upon
allowing the sample to remain at rest for some time in a flask, forming
a deposit which effervesces when heated with hydrochloric acid, and
dissolves to a solution, in which the characteristic properties of a
lime salt can be recognized.
_Bicarbonate of soda._--In presence of this compound the milk possesses
a strongly alkaline reaction, furnishes a serum having a sharp and
bitter taste, and leaves a residue of the salt upon evaporation.
_Emulsion of almonds._--The milk has a specific gravity of at least,
1.033. If it is passed through a gauze, small opaque lumps are
separated. When examined under the microscope, numerous minute globules,
having a diameter of 1/400 of a millimetre, are observed, and, upon
adding a few centigrammes of amygdaline to one or two grammes of the
milk, the characteristic odor of bitter almonds is produced.
_Gum tragacanth._--When shaken in a glass flask and allowed to rest, the
milk deposits on the sides small transparent lumps, which usually
present a slightly elongated or angular form.
_Gum arabic._--The addition of alcohol produces an abundant white opaque
precipitate.
_Starch, flour, decoction of barley, rice, etc._--Upon boiling the
suspected milk, and adding tincture of iodine, the amylaceous substances
present produce a blue coloration in the fluid.
_Sugar._--If yeast is added, and the mixture allowed to stand for some
time at a temperature of 30°, alcoholic fermentation ensues; under these
circumstances, lactose does not undergo fermentation.
_Cerebral substances._--Adulteration by these substances is probably of
much less frequent occurrence than was formerly supposed. The admixture
is detected by evaporating the milk to dryness, dissolving the residue
in ether, evaporating the etherial solution, and fusing the second
residue, which consists of fatty matters, with nitrate of potassa in a
platinum crucible. The mass is then taken up with water, and chloride of
barium added to the solution. If cerebral substances were contained in
the milk, ether will dissolve the fatty matters present, the phosphorus
of which is converted into a soluble phosphate by the calcination with
nitrate of potassa and is thrown down as a white precipitate, upon the
addition of a solution of chloride of barium. This test may be confirmed
by a microscopic examination of the milk, when the peculiar appearance
of cerebral matter will be detected.[U]
[U] Fragments of nerves, and other organic structures, are frequently
observed in this examination.--_Trans._
WINE.
The most common adulteration to which wines are subjected is the
addition of water: wines having a rich color are frequently mixed by the
dealer with lighter wines, and the fraud consummated by adding water.
The detection of this adulteration is somewhat difficult, as water is a
normal constituent of wine. In Paris the following method is usually
employed: As soon as the wine is confiscated, it is ascertained what
kinds of wine are manufactured by the inculpated dealer, and a statement
obtained from him, giving the proportions of alcohol, etc., contained in
the various brands. A wine is then prepared, according to the
information received, an estimation of the alcohol contained in the
prepared sample made, and the results compared with those furnished by a
similar examination of the suspected wine. In case the proportion of
alcohol is less in the suspected wine than in the prepared sample, it is
evident that a fraudulent adulteration has been committed. If, however,
the quantity of alcohol is the same in both wines, it does not
necessarily follow that the wine has escaped admixture, since this body
may have been added after the adulteration with water. In addition to
the estimation of alcohol, it is also necessary to determine the amount
of cream of tartar (bitartrate of potassa) present, as the proportion of
this salt would be sensibly decreased by the addition of alcohol and
water to the wine. This fraud could, however, be disguised by
subsequently adding the proper amount of cream of tartar.
It is also well to ascertain if two equal quantities of the prepared
sample and the wine under examination require the same amount of
solution of hypochlorite of lime for decolorization. In case the
suspected wine has been adulterated, the quantity of hypochlorite
solution used will be less than the amount necessary to decolorize the
prepared wine. Foreign coloring matter may be added by the adulterator,
but this fraud is easily detected by adding potassa to the sample: if
its coloration is natural, a green tint is produced; whereas, if foreign
matter has been introduced, the wine assumes various other colors upon
the addition of the alkali.[V]
[V] _Cotlini_ (_Ann. du genie civil_, No. 3, 1873) states that the
following reactions occur when artificially colored wines are heated
with potassa:
Pure wine no precipitate greenish hue
Elderberry violet "
Beet-sugar red "
Logwood red violet-red "
Privet violet-blue "
Turmeric light-blue "
According to _M. de Cherville_ (_Quar. Jour. Sc._), a bright violet
coloration is produced in the above test, if litmus be present.
Fuchsin is separated by treatment with subacetate of lead and
addition of amylic alcohol (_Jour. de Ph. et de Ch. Mar.
1873_).--_Trans._
The indications furnished by the above test are rendered valueless, if
the wine has been artificially colored by the addition of the coloring
matter of grape-skins; but the execution of this fraud would require
some knowledge of chemistry, and fortunately adulterators, as a class,
are deficient in this branch of science.
Another method for detecting the addition of water is based upon the
fact that fermented liquors do not contain air in solution, but only
carbonic acid; whereas, water dissolves oxygen and nitrogen. It is
executed as follows:
The wine to be tested is placed in a flask, the delivery-tube of which
is also filled, and heated; the evolved gas being collected in a tube
filled with mercury. In case the wine is pure, the disengaged gas will
be completely absorbed by potassa; if, on the other hand, water has been
added, an unabsorbed residue, consisting of oxygen and nitrogen, will
remain.
This test is useless in case water, through which a current of carbonic
acid gas has been passed for a considerable time, has been employed.
Under these circumstances, however, the presence of the gas would
probably be detected by the taste of the wine, as well as by the
estimation just mentioned, since the sample would invariably contain a
larger proportion of the gas than the standard with which it is
compared; indeed, it would be almost impossible to prepare a solution
which contained exactly the proportion of carbonic acid ordinarily
present in wine.
It remains to mention the methods employed in determining the amount of
alcohol and cream of tartar contained in wine.
The alcometrical method usually employed is based upon the difference in
density possessed by pure alcohol and by mixtures of alcohol and water.
_Gay-Lussac_ has proposed an areometer (_alcoholmeter_), provided with a
scale which directly indicates the proportion of alcohol contained in a
mixture. As the indications furnished by this instrument vary with the
temperature, and the scale is constructed on the basis of a temperature
of 15°, a correction of the results obtained is necessary if the
determination is made at other temperatures. Gay-Lussac has compiled a
table which indicates at once the required correction; the following
formula can also be used: _x = c ± 0.4 t_, where _x_ is the quantity of
alcohol present in the sample; _c_ the degree indicated by the
alcoholmeter, and _t_ the number of degrees differing from the
temperature of 15°: the second member of the formula is subtracted from,
or added to the first, as the temperature at which the estimation is
made is greater or less than 15°.[W]
[W] Tralles alcoholmeter is almost exclusively employed in this
country.--_Trans._
In case the wine to be examined contains substances other than water
and alcohol, which would affect its density, it is necessary, before
making use of the alcoholmeter, to distil the sample and subsequently
examine the distillate, which will consist of a simple mixture of water
and alcohol. Usually the distillation is discontinued as soon as
one-third of the sample has passed over, and a quantity of distilled
water, sufficient to render the volume of the mixture equal to the
original volume of the wine, added to the distillate: the fluid
remaining in the flask will be entirely free from alcohol. The addition
of water to the distillate is not indispensable, but otherwise it is
necessary to divide the degrees indicated by the alcoholmeter by 3, in
order to reduce the result to the original volume of the wine taken.
_M. Salleron_ offers for sale a small apparatus (Fig. 20) used in
examinations of this character, consisting of a flask, closed with a
gutta-percha cork, containing a tube which connects with a worm passing
through a cooler. The flask is supported by an iron stand, and heated
with a gas or spirit lamp.
[Illustration: Fig. 20.]
In order to estimate the cream of tartar, the wine is evaporated to the
consistency of an extract, alcohol of 82° B. added, and the residue
obtained calcined in a crucible. The amount of salt present in the fused
mass is then determined by the alkalimetric method, as directed in all
works on quantitative analysis. The carbonate obtained from 1 gr. of
cream of tartar exactly saturates 9.75 cubic centimetres of a solution
containing 100 grammes of sulphuric acid of 66° B., and 1800 grammes of
distilled water.
The detection of toxical substances, often contained in wine, is
accomplished by the methods described under the head of detection of
poisons.
VINEGAR.
Vinegar is frequently adulterated with water, and occasionally sulphuric
acid is added to artificially increase its acidity.
The ordinary reagents--such as chloride of barium, or nitrate of
silver--are not adapted to the direct detection of sulphuric acid, or of
other mineral acids, as sulphates and chlorides, which are as readily
precipitated as the free acids, may also be present.
The following method, proposed by _M. Payen_, is usually employed:
Five centigrammes of starch (fecula) are added to a decilitre of table
vinegar, the mixture boiled for 12 or 15 minutes, and, after the fluid
has become _completely cooled_, a few drops of iodine solution added:
dilute acetic acid does not affect starch, and, in case the vinegar is
pure, a blue coloration is produced; if, on the other hand, even a
minute quantity of a mineral acid be present, the starch is converted
into dextrine, and the addition of iodine fails to cause a blue
coloration.
The water present is indirectly estimated by determining the amount of
acetic acid contained in the vinegar. This can be accomplished in
different ways: either the quantity of a standard solution of an alkali,
necessary to exactly neutralize a measured quantity of the vinegar, is
ascertained, or the vinegar is supersaturated with solution of baryta,
the excess of the salt eliminated by conducting carbonic acid through
the fluid, the precipitate removed by filtration, and the baryta salt in
the filtrate precipitated by the addition of sulphuric acid. The second
precipitate is then collected on a filter, washed, weighed, and the
amount of acetic acid present calculated: this is done by multiplying
its weight by 0.515.
SULPHATE OF QUININE.