The following is a copy of my report to the _Grocer_ on a sample of the
ingredients actually used by the Chinese for coloring of tea, which
sample was sent to the _Grocer_ office by a reliable correspondent
at Shanghai (November, 1873). I reprint it because the subject has a
general interest and is commonly misunderstood:
I have examined the blue and the yellowish-white powders received from
the office, and find that the blue is not indigo, as your Shanghai
correspondent very naturally supposes, but is an ordinary commercial
sample of Prussian blue. It is not so bright as some of our English
samples, and by mere casual observation may easily be mistaken for
indigo. Prussian blue is a well-known compound of iron, cyanogen,
and potassium. Commercial samples usually contain a little clayey or
other earthy impurities, which is the case with this Chinese sample.
There are two kinds of Prussian blue—the insoluble, and the basic or
soluble. The Chinese sample is insoluble.
This is important, seeing that we do not eat our tea-leaves, but merely
drink an infusion of them; and thus even the very small quantity which
faces the tea-leaf remains with the spent leaves, and is not swallowed
by the tea-drinker, who therefore need have no fear of being poisoned
by this ornamental adulterant.
Its insolubility is obvious, from the fact that green tea does not give
a blue infusion, which would be the case if the Prussian blue were
dissolved.
There are some curious facts bearing on this subject and connected with
the history of the manufacture of Prussian blue. Messrs. Bramwell, of
Newcastle-on-Tyne, who may be called the fathers of this branch of
industry, established their works about a century ago. It was first
sold at two guineas per lb.; in 1815 it had fallen to 10_s._ 6_d._, in
1820 to 2_s._ 6_d._, then down to 1_s._ 9_d._ in 1850. I see by the
Price Current of the _Oil Trade Review_ that the price has recently
been somewhat higher.
In the early days of the trade a large portion of Messrs. Bramwell’s
produce was exported to China. The Chinese then appear to have been the
best customers of the British manufacturers of this article. Presently,
however, the Chinese demand entirely ceased, and it was discovered that
a common Chinese sailor, who had learned something of the importation
of this pigment to his native country, came to England in an East
Indiaman, visited, or more probably obtained employment at a Prussian
blue manufactory, learned the process, and, on his return to China,
started there a manufactury of his own, which was so successful that
in a short time the whole of the Chinese demand was supplied by native
manufacture; and thus ended our export trade. Those who think the
Chinese are an unteachable and unimprovable people may reflect on this
little history.
The yellowish powder is precisely what your Shanghai correspondent
supposes. It is steatite, or “soapstone.” This name is very deceptive,
and coupled with the greasy or unctuous feel of the substance,
naturally leads to the supposition that it is really as it appears, an
oleaginous substance. This, however, is not the case. It is a compound
of silicia, magnesia, and water, with which are sometimes associated
a little clay and oxide of iron. Like most magnesian minerals, it has
a curiously smooth or slippery surface, and hence its name. It nearly
resembles meerschaum, the smoothness of which all smokers understand.
When soapstone is powdered and rubbed over a moderately rough surface,
it adheres, and forms a shining film; just as another unctuous mineral,
graphite (the “black-lead” of the housemaid), covers and polishes
ironwork. On this account, soapstone is used in some lubricating
compounds, for giving the finishing polish to enameled cards, and for
other similar purposes.
With a statement of these properties before us, and the interesting
description of the process by your Shanghai correspondent, the whole
riddle of green-tea coloring and facing is solved. The Prussian blue
and soapstone being mixed together when dry in the manner described,
the soapstone adheres to the surface of the particles of blue, and
imparts to them not only a pale greenish color, but also its own
unctuous, adhesive, and polishing properties. The mixture being well
stirred in with the tea-leaves, covers them with this facing, and thus
gives both the color and peculiar pearly lustre characteristic of some
kinds of green tea. I should add that the soapstone, like the other
ingredient, is insoluble, and therefore perfectly harmless.
Considering the object to be attained, it is evident from the above
that John Chinaman understands his business, and needs no lessons from
European chemists. It would puzzle all the Fellows of the Chemical
Society, though they combined their efforts for the purpose, to devise
a more effective, cheap, simple, and harmless method of satisfying the
foolish demand for unnaturally colored tea-leaves.
When the tea-drinking public are sufficiently intelligent to prefer
naturally colored leaves to the ornamental stuff they now select, Mr.
Chinaman will assuredly be glad enough to discontinue the addition
of the Prussian blue, which costs him so much more per pound than
his tea-leaves, and will save him the trouble of the painting and
varnishing now in demand.
In the meantime, it is satisfactory to know that, although a few silly
people may be deceived, nobody is poisoned by this practice of coloring
green tea. I say “a few silly people,” for there can be only a few,
and those very silly indeed, who judge of their tea by its appearance
rather than by the quality of the infusion it produces.
With these facts before us it is not difficult to trace the origin of
the oft-repeated and contradicted statement that copper is used in
coloring green tea. One of the essential ingredients in the manufacture
of Prussian blue is sulphate of iron, the common commercial name which
is “green copperas.” It is often supposed to contain copper, but this
is not the case.
Your Shanghai correspondent overrates the market value of soapstone
when he supposes that Chinese wax may be used as a cheap substitute. In
many places—as, for instance, the “Lizard” district of Cornwall—great
veins of this mineral occur, which, if needed, might be quarried in
vast abundance, and at very little cost on account of its softness. The
romantic scenery of Kynance Cove, its caverns, its natural arches, the
“Devil’s Bellows,” the “Devil’s Post-office,” the “Devil’s Cauldrons,”
and other fantastic formations of this part of the coast, attributed to
his Satanic Majesty or the Druids, are the natural results of the waves
beating away the veins of soft soapstone, and leaving the deformed
skeleton rocks of harder serpentine behind.
“IRON FILINGS” IN TEA.
I have watched the progress of the tea controversy and the other public
performances of the public analysts with considerable interest; it
might have been with amusement, but for the melancholy degradation of
chemical science which they involve.
Among the absurdities and exaggerations which for some years past
have been so industriously trumpeted forth by the pseudo-chemists who
trade upon the adulteration panic and consequent demand for chemical
certificates of purity, the continually repeated statements concerning
the use of iron filings as a fraudulent adulterant of tea take a
prominent place. I need scarcely remark that, in order to form such an
adulterant, the quantity added must be sufficiently great to render its
addition commercially profitable to an extent commensurate with the
trouble involved.
The gentlemen who, since the passing of the Adulteration Act, have by
some kind of inspiration suddenly become full-blown chemists, have
certified to wilful adulteration of tea with iron filings, and have
obtained _convictions_ on such certificates, when, according to their
own statement, the quantity contained has not exceeded 5 per cent
in the cheapest qualities of tea. Now, the price of such tea to the
Chinaman tea-grower, who is supposed to add these iron filings, is
about fourpence to sixpence per pound; and we are asked to believe that
he will fraudulently deteriorate the market value of his commodity for
the sake of this additional 1-20th of weight. Supposing that he could
obtain his iron filings at twopence per pound, his total gain would
thus be about 1-10th of a penny per pound. But can he obtain such iron
filings in the quantity required at such a price? A little reflection
on a few figures will render it evident that he cannot, and that such
adulteration is utterly impossible.
I find by reference to _The Grocer_ of November 8th, that the total
deliveries of tea into the port of London during the first ten months
of 1872 were 142,429,337 lbs., and during the corresponding period of
1873, 139,092,409 lbs. Of this about 8½ millions of pounds in 1873,
and 10 millions of pounds in 1872, were green, the rest black. This
gives in round numbers about 160 millions of pounds of black tea per
annum, of which above 140 millions come from China. As the Russians
are greater tea-drinkers than ourselves—the Americans and British
colonists are at least equally addicted to the beverage, and other
nations consume some quantity—the total exports from China may be
safely estimated to reach 400 or 500 millions of pounds.
Let us take the smaller figure, and suppose that only one fourth of
this is adulterated, to the extent of 5 per cent, with iron filings.
How much would be required? Just five millions of pounds per annum.
It must be remembered that _coarse_ filings could not possibly be used;
they would show themselves at once to the naked eye as rusty lamps, and
would shake down to the bottom of the chest; neither could borings,
nor turnings, nor plane-shavings be used. Nothing but _fine_ filings
would answer the supposed purpose. I venture to assert that if the
China tea-growers were to put the whole world under contribution for
their supposed supply of fine iron filings, this quantity could not be
obtained.
Let anyone who doubts this borrow a blacksmith’s vice, a fine file, and
a piece of soft iron, then take off his coat and try how much labor
will be required to produce a single ounce of filings, and also bear
in mind that fine files are but very little used in the manufacture of
iron. As the price of a commodity rises when the demand exceeds the
supply the Chinaman would have to pay far more for his adulterant than
for the leaves to be adulterated. As Chinese tea-growers are not public
analysts, we have no right to suppose that they would perpetrate any
such foolishness.
The investigations recently made by Mr. Alfred Bird, of Birmingham,
show that the iron found in tea-leaves is not in the metallic state,
but in the condition of oxide; and he confirms the conclusions of
Zöller, quoted by Mr. J. A. Wanklyn in the _Chemical News_ of October
10th—viz., that compounds of iron naturally exist in genuine tea.
It appears, however, that the ash of many samples of _black_ tea
contains more iron than naturally belongs to the plant; and, accepting
Mr. Bird’s statement, that this exists in the leaf as oxide mixed
with small siliceous and micaceous particles I think we may find a
reasonable explanation of its presence without adopting the puerile
theory of the adulteration maniac, who, in his endeavor to prove that
everybody who buys or sells anything is a swindler, has at once assumed
the impossible addition of iron filings as a makeweight.
In the first place we must remember that the commodity in demand is
_black_ tea, and that ordinary leaves dried in an ordinary manner are
not black, but brown. Tea-leaves, however, contain a large quantity
of tannin, a portion of which is, when heated in the leaves, rapidly
convertible into gallo-tannic or tannic acid. Thus a sample of tea
rich in iron would, when heated in the drying process, become, by the
combination of this tannic acid with the iron it contains, much darker
than ordinary leaves or than other teas grown upon less ferruginous
soils and containing less iron.
This being the case, and a commercial demand for _black_ tea having
become established, the tea-grower would naturally seek to improve the
color of his tea, especially of those samples naturally poor in iron,
and a ready mode of doing this is offered by stirring in among the
leaves while drying a small additional dose of oxide of iron, if he can
find an oxide in such a form that it will spread over the surface of
the leaf as a thin film. Now, it happens that the Chinaman has lying
under his feet an abundance of material admirably adapted for this
purpose—viz., red hæmatite, some varieties of which are as soft and
unctuous as graphite, and will spread over his tea-leaves exactly in
the manner required. The micaceous and siliceous particles found by Mr.
Bird are just what should be found in addition to oxide of iron, if
such hæmatite were used.
The film of oxide thus easily applied, and subjected to the action of
the exuding and decomposing extractive matter of the heated leaves,
would form the desired black dye or “facing.”
The knotty question of whether this is or is not an adulteration is
one that I leave to lawyers to decide, or for those debating societies
that discuss such interesting questions as whether an umbrella is an
article of dress. If it is an adulteration, and, as already admitted,
is not at all injurious to health, then all other operations of dyeing
are also adulterations; for the other dyers, like the Chinaman, add
certain impurities to their goods—the silk, wool, or cotton—in order
to alter their natural appearance, and to give them the false facing
which their customers demand, but with this difference, if I am right
in the above explanation: that in darkening tea nothing more is done
but to increase the proportion of one of its natural ingredients, and
to intensify its natural color; while in the dyeing of silk, cotton, or
wool, ingredients are added which are quite foreign and unnatural, and
the natural color of the substance is altogether falsified.
The above appeared in the _Chemical News_ November 21, 1873, when
the adulteration in question was generally believed to be commonly
perpetrated, and many unfortunate shop-keepers had been and were
still being summoned to appear at Petty Sessions, etc., and publicly
branded as fraudulent adulterators on the evidence of the newly-fledged
public analysts, who confidently asserted that they found such filings
mixed with the tea. Some discussion followed in subsequent numbers of
the _Chemical News_; but it only brought out the fact that “finely
divided iron” exists in considerable quantities in Sheffield,—may be
“begged,” as Mr. Alfred H. Allen (an able analytical chemist, resident
in Sheffield,) said. The fact that such finely divided iron is thus
without commercial value still further confirms my conclusion that it
is not used for the adulteration of tea. If it were, its collection
would be a regular business, and truck-loads would be transmitted from
Sheffield to London, the great centre of tea-importation. No evidence
of any commercial transactions in iron filings or iron dust for such
purposes came forward in reply to my challenge.
The practical result of the controversy is that iron filings are no
longer to be found in the analytical reports of the adulteration of
tea.