CEYLON HYBRID TEA-LEAF.
JAVA TEA-LEAF.
SKELETON OF GENUINE TEA-LEAF.
But in order to better detect the presence of spurious leaves in tea a keener knowledge of the botanical formation of the true tea-leaf is requisite, for which purpose the use of a microscope will be found an invaluable aid. Tea-leaves in general construction bear a strong resemblance to those of the willow and many other plants of the kind, vary widely in size and form, being much smaller, more deeply serrated, and ending more regularly just short of the stalk. The venations are very characteristic, the veins running out from the middle rib, almost parallel with each other, altering their course before reaching the extremities, and turning so as to leave a bare space within the border. When infused and unfolded it is of a bright-green color, the loopings together of the principal veinings in the true leaf being very characteristic. While the spurious leaf is either of a greenish-yellow or reddish-brown color, and irregular in form under the same conditions or when deprived of its cosmetics.
To still better distinguish between them treat a sample of the suspected tea as in making an ordinary infusion to soften and expand the leaves, then separate and uncurl them and lay flat on a piece of glass or other smooth surface for comparison with the genuine leaf. Next see that they agree in description and formation, but more especially in the venations and serrations. Or soak the leaves in hot water, and carefully unroll and closely examine their formation and structure and then compare closely. The epidermis of the lower surface of the true leaf can be with a little caution detached in small portions with a sharp razor, and then analyze the frame or skeleton of the leaf in a little water or glycerine, under a microscope, comparing the venations and serrations with those of the genuine tea-leaf. Still another simple and inexpensive test is to boil a few of the suspected leaves for a minute or two on a watch glass, with a little distilled water, and add an equal portion of burnt magnesia, treating the whole until it is reduced to a large-sized drop. If no crystalline sublimate is obtained therefrom by the operation the leaves cannot be those of genuine tea.
Chemically an examination of the ash of tea-leaves also affords some criteria which may also be utilized for the purpose of identifying the true tea-leaf. For instance, in common kinds of wood, such as oak, deal and pine, the proportion of ash is a few-tenths per cent. of the whole, and by taking wood in its ordinary air-dried condition it contains some 20 to 30 per cent. of moisture. Leaves, on the other hand, contain 10, 20 and even 30 times as much mineral matter, there being doubtless a connection between this abundance of mineral matter and the active chemical changes which take place in the leaves during the growth of the plant. In tea-leaves, therefore, as in leaves in general, the ash amounts to a considerable percentage, usually averaging about 6 per cent., so that a chemical examination of the ash forms an important part of the analysis of tea. The proportion of ash in all teas is tolerably constant, genuine tea rarely yielding so little as 5 and never exceeding 6 per cent. of ash on incineration. Therefore, to determine the amount of ash, weigh a small quantity of the tea in its ordinary commercial state and burn it in a platinum crucible and then re-weigh the resultant ash; by observing a few simple precautions very constant and accurate results are attainable by this method. The crucible should be clean and bright, the lid fitting precisely; an iron triangle, covered with a tobacco pipe may be employed to support the crucible during ignition. The operation is then commenced by igniting the empty crucible, and allowing it to cool, being placed for that purpose on a piece of porcelain or iron, immediately weighing the crucible on becoming cold. Next place one or two grams of tea in the crucible, weighing both together, and ignite over a spirit lamp or good gas-burner, stirring the contents with a platinum wire for a few minutes. When ignition is complete the crucible is covered with the lid, let cool again and immediately weighed a second time. If there is any doubt as to the completeness of the ignition, the crucible must be again ignited, and if there is no difference in weight, the ignition is thereby proved finished. As is obvious, in order to obtain accurate results it is indispensable that the crucible should be in the same condition when it is weighed empty and when weighed with the ash, and this is insured by the preliminary ignition and rapid re-weighing, as above described.