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precipitated by the addition of 200 cubic centimetres of alcohol of 90 per cent. The precipitate, which appears as a transparent gelatinous mass, is separated by filtration, re-dissolved in a little water, and again precipitated as before. The precipitate when well washed is dried and weighed on a tared filter. A portion is then ignited to ascertain the amount of ash present, and the remainder is boiled for four hours with water acidulated with 10 drops of sulphuric acid to convert any dextrin or similar substance into glucose. The weight of ash and dextrin, if any, is deducted from the weight of the alcoholic precipitate previously ascertained, the difference being regarded as the percentage of pectin and pectic acid present.
Dextrin.-The proportion of dextrin or gum is ascertained from the amount of sugar produced by boiling the alcoholic precipitate with dilute sulphuric acid, as in the above process for the estimation of pectin. The quantity of sugar formed is determined by an alkaline copper solution, as described on page 107, from which result the dextrin can be readily calculated : 100 parts of glucose or 95 parts of cane sugar being equal to 90 parts of dextrin.
Cellulose. The percentage of cellulose cannot be determined by direct analysis, and the process followed is usually an indirect one. The amount of cellulose is represented by the portion insoluble in alcohol and water, less the mineral matter, and insoluble albumin. The ash is obtained by igniting a known weight of the dry residue, and the albumin, as before stated, by combustion with copper oxide. The difference is the percentage of cellulose and insoluble colouring matter present in the tea.
Chlorophyll and Resin.-Fifty grains of the dry and finelypowdered tea are left in contact with ether for twenty-four hours. The ether is passed through a filter, and the tea-powder washed with warm ether. The filtrate is evaporated to dryness, and treated with hot water to dissolve out any substances soluble
therein. The portion insoluble in water is then dried and weighed.
The powder left after treatment with ether is shaken up with alcohol for some time, the alcoholic extract is filtered and gently evaporated to dryness. The residue is exhausted with benzol, and, after filtering and evaporating the benzol, the extract is treated with boiling water, as in the former part of the process. After removing the water, the resinous mass is dried and weighed. To this result is added the quantity of extract obtained by ether; the sum multiplied by 2 gives the percentage shown as "chlorophyll and resin."
At one time there were probably few articles so generally adulterated as tea, especially when its price was such as to hold out strong inducement for the manufacture and sale of a spurious commodity. The sophistication was carried on both in China and in this country; but for many years past the adulteration of tea has been effected almost entirely before its importation.
The spurious teas manufactured in this country were composed sometimes of exhausted tea-leaves, and sometimes of the leaves of other plants, such as the elder, the sloe, and the willow. The leaves, when made up to represent green tea, were generally prepared with some of the following substances: viz. gum, Dutch pink, Prussian blue, indigo, carbonate of magnesia, French chalk, and sulphate of lime; and, when made to represent black tea, the leaves were slightly coloured with Dutch pink to impart a bloom.
The sophistication of teas imported from China has most fre
quently consisted of partially exhausted leaves, and of leaves made up with a large proportion of sand or broken quartz, by the aid of a little gum, and then skilfully rolled and re-dried so as to resemble ordinary commercial teas. Plumbago was generally employed to give uniformity of colour to black, and a mixture of Prussian blue. and soapstone to green teas.
Happily, at the present time, a great change has taken place for the better in the quality of the teas found in commerce and supplied to the public. It is now of very seldom occurrence that quartz or foreign leaves are found mixed with tea, or that colouring matters to the same extent, or in the same variety as formerly, are discovered to have been used in facing tea.
The adulterants of tea may be classed under three heads:
Ist. Those substances which can be detected by their physical properties—such as foreign leaves, quartz, excess of sand, and certain colouring matters.
2nd. Those which can be distinguished by their chemical properties-for example, Prussian blue, clay, soapstone, gum, rice-water, etc.
3rd. Partially exhausted leaves.
The quartz and sand are usually made up with the tea when in a soft and flaccid condition, and are ingeniously concealed in the nodules formed of the leaves. Sometimes irregular grains of quartz have been simply coloured with plumbago or other substance, and so made to closely resemble some kinds of genuine caper tea, with which they have been mixed.
Magnetic oxide, sometimes referred to in the trade as iron filings, is found associated with quartz and sand in tea.
An attempt at explaining the presence of this compound has been made by attributing it to the ferruginous character of the soil on which, in some localities, the tea plant has been cultivated,
but the quantity found is often much too large to be accounted for by the accidental admixture of portions of the soil during the process of gathering the leaves.
The object of adding Prussian blue, China clay, and similar substances intended to impart a greenish tint appears to be twofold, namely, to improve and give uniformity to the colour of bonâfide green tea, and also—which is very reprehensible-to give to old and inferior black tea the appearance and external character of green.
In adding the colour, the leaves are usually moistened with rice-water and re-heated. Whilst in this condition, the finelypowdered colour is shaken on the tea, which is continuously stirred, until a uniform tint is obtained. Sometimes a little yellow colour such as turmeric is added first, and then the Prussian blue or indigo; in other instances, the Prussian blue mixture alone appears to have been used.
Some years ago large quantities of exhausted leaves were collected in this country, and, after the addition of gum and other matters, were rolled and re-dried so as to resemble genuine tea. This spurious tea was mixed with tea as imported and sold to the public as genuine, whereby a very serious fraud was perpetrated. By the vigilance of the authorities this practice was suppressed, and we believe that it has never since been successfully resumed. It has occasionally happened that an importation of tea has been submerged in sea-water; in some instances such tea has been re-dried and brought into the market, but perhaps more frequently re-shipped to another country. From the present general soundness, however, of the tea trade, the sale of such a description of tea has been reduced to a minimum.
It is well known that the manufacture of spurious tea has been carried on to a considerable extent in China, and that large quantities of the sophisticated article have been imported from
time to time into this country, some of which has been known in the market by the name of the "Mahloo Mixture." Owing, however, to the rigid scrutiny to which tea is now subjected, it is likely that the quantity of such spurious teas passed into this country will become very small.
It has been seen that the adulterants of tea may be conveniently studied under three heads-viz. :
Substances which can be detected by their physical
2nd. Mineral salts, along with some organic substances, all of which have distinctive chemical reactions.
3rd. Partially exhausted leaves.
When tea is treated with hot water a large proportion of the soluble organic matter of the leaf is extracted, together with some of the mineral compounds, chiefly potash salts. If in a suspected sample the problem to be solved was merely whether it consisted wholly of exhausted leaves, the proof of sophistication would be very easy. But when a portion only of the tea is in that condition the question presents greater difficulty. This arises from the fact that in vegetable products, tea amongst the rest, nature has provided no hard-and-fast line as to the proportion in which the soluble or characteristic constituents may be present. Where a given test, say that of the total water extract is relied upon and applied to a number of teas, great difference exists between the maximum and minimum results. It is obvious, therefore, that a considerable admixture of a spurious tea could be added to one of the better kinds without reducing the amount of extract below that obtained from a genuine though inferior
It will be found difficult in practice to separate individual exhausted leaves. Where this can be done, the results of an analysis of them would no doubt be conclusive. Usually it is necessary to weigh out a given quantity-say 100 grains of the