effects. These quantities are, however, mostly too minute to be detected in the water in its unconcentrated condition, and to effect its determination it is always necessary to evaporate it to a smaller bulk. This operation is performed in porcelain dishes, with the addition of a drop or two of hydrochloric acid, so as to slightly acidulate the water. If by the addition to a portion of this concentrated liquid of a few drops of sulphuretted hydrogen dissolved in water, a dark coloration is produced, one of the series of the heavy metals is sure to be present. This may be either copper or lead, but in most cases the latter metal. To ascertain which of them is present in a special case, much larger quantities of the water must be evaporated and tested. From three to four litres of water are evaporated to a small bulk, with the addition of a few drops of nitric acid. Sulphuretted hydrogen is passed through the liquid for about three or four hours, and the black precipitate which forms, if either lead or copper is present, is collected on a filter and washed with water containing some sulphuretted hydrogen. It is then boiled with pure nitric acid and evaporated on the water-bath, with the addition of a drop of sulphuric acid, and moistened again with distilled water. The residue, if any, consisting of sulphate of lead, is collected on a filter, and the filtrate tested after neutralisation with ammonia and acidulation with acetic acid, with a solution of ferrocyanide of potassium, which will give rise to a red precipitate if any copper be present.

The quantitative estimation of either metal is usually effected by a colorimetrical process-namely, by comparing the depth of colour produced by sulphuretted hydrogen in the water to be examined with that produced in a solution of lead of known strength, in precisely analogous manner as the colorimetrical determination of ammonia in water. The details are, therefore, evident to every one who is acquainted with this latter process, and need no description. The standard solution is prepared by dissolving a known quantity of crystals of pure acetate of lead.

Estimation of suspended matters.-A large quantity of the turbid water, say 1 litre, is filtered through a dried and weighed filter, which is then redried and again weighed. Thus the total suspended matter is obtained. It is subsequently incinerated in a weighed platinum crucible, and in this manner the proportion of mineral and organic suspended matter is arrived at. The substances in suspension are frequently so finely divided that they pass through the best filter paper, and sometimes they settle with such extreme slowness, that the estimation becomes practically impossible. A quantitative analysis of the mineral portion is seldom required, although it may be desirable in some cases to test it qualitatively. Again, when the sediment is thus collected a good opportunity is presented for a further microscopical examination.

CHAPTER IV.

TEA AND ITS ADULTERATIONS.

DEFINITION OF ADULTERATION.

Leaves other than those of tea, except those used for scenting; exhausted tea-leaves and damaged tea; an undue proportion of stalks or vegetable matter foreign to tea, of any kind whatever; foreign mineral matter, especially sand, quartz, soapstone, China clay, magnetic oxide of iron, &c. Lastly, the substances used for artificially colouring or painting the teas, as ferrocyanide of iron, or Prussian blue, indigo, turmeric, &c.

Growth and Preparation.

THE tea-plant, Thea sinensis, is a hardy evergreen flowering shrub, attaining the height of from three to six feet and upwards. It belongs to the natural family Columniferæ, Ternstræmiacea of Lindley, which includes the camellias and myrtles. The tea-plant occurs indigenously or is specially cultivated in China, Japan, parts of India, especially the southern side of the Himalayas, and in Western Africa but the plants will grow in many other mild climates, and it is stated that they will flourish in all latitudes from the equator up to 40°. It is usually propagated from seed; the seedlings when a year old are planted in rows, three or four feet apart. They come to maturity in three or four years, yielding in the course of the season three, and in some cases four, crops of leaves. When ten or twelve years old, the plants are dug up and replaced by other seedlings.

The first gathering takes place early in the spring, the second in the beginning of May, the third about the middle of June, and a fourth in August. The leaves of the first gathering are the most valuable, and from these Pekoe tea, which consists of the young leaves and leaf buds, as well as black teas of the highest quality, are prepared. The leaves of the last gathering are large and old, and inferior in flavour and value.

The use of tea became general in China about the year 600, but it was not until the seventeenth century that it was brought to Europe.

The teas of commerce are divided into black and green. All the varieties of these are derived from the same species of tea-plant, the

differences depending upon soil, climate, age of the leaves, and mode of preparation. The plants from which black teas are prepared are grown chiefly on the slopes of hills and ledges of mountains, while the green teas are cultivated in manured soils; other differences between the two kinds of tea are occasioned by the processes adopted in the preparation and roasting of the leaves. Thus, the leaves of black tea are allowed to lie in heaps for ten or twelve hours, during which they undergo a species of fermentation, and it is this which occasions them to assume a dark colour They are then tossed about till they become flaccid. They now emit the characteristic odour of tea; the leaves are next rolled with the hands into balls on a wooden table, and much liquid is said to be expressed from them. 'After which they are shaken out, roasted for a few minutes, again rolled, and while still flaccid are exposed to the air for some hours upon shallow bamboo trays; this alternate heating and rolling is repeated three or four times, and finally the leaves are dried slowly over charcoal fires.' Those of green tea are not subjected to this preliminary fermentation, but are roasted 'within an hour or two after they have been gathered, in pans over a brisk wood fire. After four or five minutes' roasting the leaves become flaccid and are rolled by the hands upon a wooden table; they are then again thrown into the drying pans, where they are kept in rapid motion, and in about an hour and a half are completely dried' (Watts). But the leaves thus prepared are of a vellowish or olive-green tint, very unlike the colour of the painted green teas imported into this country from China.

The outward characters of certain teas depend upon the rolling to which the leaves are subjected, an operation which is three or four times repeated in the case of superior teas, before the drying and rolling are considered to be complete.

The Scenting of Tea.-To certain descriptions of tea an artificial odour or scent is imparted. This is communicated to the teas chiefly by means of the Chulan flower, Chloranthus inconspicuus; those of Olea fragrans, Gardenia florida, and Jasminum sambac are, however, also sometimes used for the purpose. Two processes are adopted for the scenting of the tea. In some cases the fresh flowers are strewn between successive layers of tea, and both are then roasted until the flowers become crisp, when they are sifted out. In others the flowers are dried, powdered, and then sprinkled over the tea.

The principal kinds of black tea are Bohea, the commonest description, Congou, Souchong, Caper, and Pekoe, which last is of the highest quality, consisting of the unexpanded leaves and buds, which, when clothed with hairs or down, constitute Flowery Pekoe; but the three last named teas really possess more the characters of green than of black teas. The chief varieties of green tea are Twankay, Hyson Skin, Young Hyson, Hyson, Imperial, and Gunpowder, this last corresponding in green tea with Flowery Pekoe. Imperial, Hyson and Young Hyson consist of the second and third gatherings, while the light and inferior

leaves separated from Hyson by a winnowing machine constitute Hyson Skin, in much demand amongst the Americans.

Fig. 18.

The scented

D

B

or mixing constitutes a special art or business, and so particular are most large and wholesale firms, that they always keep portions of the first mixings to serve as standards or guides for the next mixing; uniformity of quality, so much desired by many customers, being thereby obtained.

The form of the leaves.—The leaves vary considerably in size and form, according to age. The youngest leaves are narrow, downy, and present slight evidences of serration. Those next in age and size have their edges delicately serrated, with the venation but little perceptible; in those of medium and large sizes the venation is well marked, a

Fig. 19.

Leaf of the Assam variety of the TEA-PLANT; the venation is the same as in the black and green varieties, but there is a slight difference in the serrations, which are alternately large and small-a difference which is probably not

constant.

series of characteristic loops being formed along each margin of the leaves, the serrations being stronger and deeper and wider apart. Sometimes, as in the Assam variety of the tea-plant, the serrations are alternately large and small, a difference which is probably not con

stant.

The form, serration and venation of the tea-leaf are usually sufficiently characteristic to distinguish it from most other leaves with which tea is liable to be mixed, but in cases of doubt or difficulty most valuable aid is obtained by a knowledge of the minute structure of the leaf as shown by the microscope.

Minute structure of the tea-leaf.-The tea-leaf is made up of epidermic cells, parenchimatous cells, stomata, hairs, and woody fibre, the latter forming the basis or skeleton of the leaf. The cells of the epidermis vary in accordance with the size of the leaf; in that of medium size the cells are small and slightly angular only, while in the hard and old leaf they are larger, more angular, and the walls of the cells are more