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solved out with water, but the amount is less than 1 per cent. Like ordinary casein and coagulated albumin, it is dissolved by alkalis; but its separation by this means from the cellulose of the leaf is unsatisfactory.
The cellulose of tea is readily acted on by the fixed alkalis, so that the albumin can be only partially recovered in an impure state. The amount of this substance may be more accurately determined by thoroughly exhausting the leaf, first with alcohol and then with water, and estimating the nitrogen in the portion of the leaf remaining insoluble, reckoning the quantity so obtained as being all derived from albumin.
When the nitrogen, associated with the cellulose in the form of vegetable albumin, is deducted from the total amount of nitrogen found in the leaf, a quantity remains which cannot be accounted for by any proportion of theine which has as yet been fairly obtained from tea. The alcoholic extract, therefore, either contains a larger amount of theine than has been recovered from it, or there is present a quantity of another and undetermined nitrogenous substance.
Gum or Dextrin.—Substances under the indefinite term of 66 gum are stated by chemists to be present to the extent of from 5 to 9 per cent. We have found, however, in samples of black and green teas, the analyses of which are given above, that dextrin, arabin, or similar gum, convertible into sugar by sulphuric acid, was practically absent. It is true that about 1⁄2 per cent. of a gum corresponding to dextrin was found in the green tea ; but unless the Chinese are exonerated from the suspicion of using such a gum in making up green teas, it is open to question whether even this small proportion is natural to the leaf.
Pectin, etc.-The characteristic gummy matter of tea appears to be pectin and pectic acid. It is obtained in considerable purity from the water extract after the tea has been well exhausted by alcohol. It is precipitated by alcohol in presence of hydrochloric acid as a transparent jelly, the reactions of which, on
subsequent treatment with acids and alkalis, are those of pectin
and pectic acid.
Sugar. Neither of the two descriptions of tea gave any indication of sugar. The tannin of the green tea gave, after boiling with a little dilute mineral acid, 133 per cent. of glucose, indicating that a portion of it existed as a glucoside. Under similar conditions the tannin of the black tea gave no sugar.
Tannin. This is the most abundant substance found in the soluble part of the tea-leaf. Although in some degree it answers to ordinary gallo-tannic acid in its reactions, yet, from its instability and the modifications it undergoes under chemical treatment, we are inclined to the opinion that it differs from that acid in some important respects.
Chlorophyll and Resin.—Tea contains a small quantity of certain substances soluble in ether and benzol, and insoluble in water. These chiefly consist of chlorophyll and resinous bodies. It is probable that the amount obtained from tea is greater than what was originally present in the leaf, as some of the tannin and other constituents are liable to be changed by oxidation into a resinouslike substance.
Cellulose. The cellulose or woody fibre, which is insoluble in water, forms a considerable proportion of the tea-leaf. After extracting all the soluble constituents of the tea with water, there are left associated with the cellulose nearly all the albumin, part of the ash, and a little of the colouring matter. These cannot be well separated without loss of cellulose, the estimation of which has consequently to be determined by difference.
Ash. The following table exhibits the composition of the ash of seven descriptions of tea, including two qualities of Congou.
In these analyses of tea-ash it will be observed that soda is present in uniformly low quantities. The percentage of iron is lower than that given in some published analyses of tea-ash, but no account is given therein of the alumina which appears to be a constant constituent of the ash, and which was probably included with the iron. The presence of sulphuric acid appears to have been disregarded by most chemists. We find that it is present in remarkably constant percentages.
The sample of "Moning" gives a high proportion of total ash (829), arising from sand and silica. It will be seen on page 28 that a second sample shows only 6.88 per cent.