Tea, its history and mystery

by Joseph M. Walsh

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.