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.