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.
IRON AND STEEL FILINGS IN TEA
Are best detected by pulverizing a sample of the suspected tea and spreading the powder on a piece of glass or plate, and applying a magnet to the dust. If a quantity of the particles gravitate and adhere to it, the tea is undoubtedly adulterated in this form. While fabrications and sophistications in general may be best exposed by treating an infusion of the leaves with a watery solution of sulphuretted hydrogen or a weak solution of ammonia. Under the first treatment the liquor of pure teas will retain its natural color, but will assume a light-blue tint under the latter.
Another simpler method for those who may not have the chemicals or appliances convenient is to place a small quantity of tea-leaves in a wine-glass or goblet, pour on cold water, and stir or shake well for a few minutes. The tea, if pure, will only slightly color the water, but if adulterated, a dark-colored liquor is quickly yielded, which if boiled and let stand until cold will, if spurious, become bitter and almost transparent as it cools, while pure tea under the same conditions assumes a darker color and pleasing flavor. The latter changes arise from the tannin (a natural property in tea) of which artificial tea is entirely devoid and adulterated teas in proportion. Mineral adulterants, however, must be dealt with by the ash-test, which is unerring, spurious leaves by their botanical character and structural marks, deficiency of tannin being invariably an indication of spent or exhausted leaves.
The part of the tea which we really use being that which passes into the infusion, in other words—the Extract of tea—it is natural to look to this extract as affording the directest evidence of the quality and genuineness of a sample of tea. The extract may be regarded both quantitatively and qualitatively, and from the former point of view we are led to the tea-assay or determination of the weight of the tea-extract which a given weight of tea is capable of yielding.
In Peligot’s analyses we find the following determinations of the tea-extract—the author being quite alive to the importance of such a test:—
| GREEN TEAS. | ||
|---|---|---|
| Part soluble in boiling water. | ||
| Variety. | Dried Leaf. | Ordinary Conditions. |
| Imperial, | 43.1 | 39.6 |
| Gunpowder, | 50.2 | 49.9 |
| BLACK TEAS. | ||
| China, | 42.8 | 39.0 |
| Japan, | 45.8 | 41.5 |
| India, | 45.4 | 41.7 |
| Java, | 35.2 | 32.7 |
| Ceylon, | 44.4 | 39.8 |
These results being arrived at by the employment of a valid but rather inconvenient method of weighing out ten grams of tea-leaves and boiling them with water as long as anything is dissolved out of them, and afterwards drying up the exhausted leaves, first at a low temperature and then at a higher one, finally weighing the exhausted leaves. The loss in weight is the weight of the tea-extract, care being taken to weigh the original tea and the exhausted tea-leaves in the same state of dryness. The results, as will be observed, are stated both in the dried tea and in the tea in its ordinary commercial condition. But, instead of weighing the tea-leaves before and after extraction and taking the difference in weight as the weight of the extract there is a more convenient process—that of evaporating down the extract itself to dryness and weighing it. The drying up of the exhausted leaves and the getting them into the same hygroscopic condition as the original tea presenting considerable practical difficulties.
The evaporation of the infusion to dryness and the weighing of the dry extract is also a tedious process in its unmodified state. But if a given quantity of tea be boiled with successive portions of water no more tea-extract is yielded than if the same tea be boiled once with a large quantity of water, but whether the infusion is kept for a length of time just at the boiling-point or whether it be made to boil vigorously makes some difference in the result, brisk-boiling extracting about one-tenth more than slow boiling, so that if the boiling be very vigorous half an hour’s boiling is just as effective as an hour’s slow boiling.