may readily be detected by its striking a beautiful magenta colour with hypochoride of lime or bleaching powder. For the success of this test it is necessary that the indigo should be but little contaminated with organic matter.

A method of quantitative estimation might be founded upon its property of being destroyed and decolorised by a solution of permanganate of potash. For this purpose a solution of indigo and sulphuric acid of known strength should be made; it should be determined by experiment how much of a solution of permanganate would be required for its discoloration. The indigo obtained from a weighed quantity of tea is then dissolved by means of sulphuric acid, and the amount of permanganate solution necessary to its complete discoloration is likewise estimated. Thus all the data would be obtained which are necessary for the calculation of the amount of indigo present in the tea.

On the detection of turmeric.-The microscope is the only means of identifying turmeric. It consists of characteristic yellow cells, of a rounded form, which are filled with starch granules of a peculiar shape. The cells on the addition of an alkali turn brown, swell up, and the outlines of the large starch granules become visible (see ' Turmeric').

On the detection of black lead.-The jet black glossy and metallic lustre imparted to substances coated with this material is so characteristic as to serve in most cases for its identification. Apart from the evidence afforded by the eye alone, it may be detected in other ways. If a thin slice be removed from the surface of one of the leaves faced with this substance, and placed under the microscope, it will be seen to be thickly studded with numerous black particles.

Again, if one or two teaspoonfuls of black-leaded tea be infused in boiling water, the liquid will in many cases, where the quantity of facing is considerable, acquire a blackish hue, and on evaporation the bottom of the vessel containing it will be found to exhibit the dark, shining and characteristic coating of black lead.

Another method will be to pass the washings through a weighed filter, which will retain the black lead which may then be estimated. Black lead consists principally of carbon, with a variable amount of oxide of iron, usually about 5 per cent.

On the detection of China clay.-The matter entering into the facing of the tea must be removed, as already pointed out, by rapidly washing with cold water, and then obtained from the washings by subsidence. The deposit must be dried, ignited, weighed, and tested first qualitatively and then quantitatively if required, which it rarely will be, for silica and alumina, its two principal constituents. In this case, as in that of silicate of magnesia or soapstone, it will be necessary to fuse the powder with carbonate of potash to effect its decomposition and the formation of a soluble silicate.

On the detection of silicate of magnesia or soapstone.-The powder is collected and decomposed, as before described, and tested for silicic acid and magnesia.

The detection of sulphate of lime or gypsum.-The leaves of tea, especially those from Assam, are sometimes dusted over with sulphate of lime, and this when no other colouring substances are employed.

The sulphate must be separated, as before described, and the ash treated with hydrochloric acid; in the solution, after dilution with water, the sulphuric acid and the lime may be detected and estimated as follows:-One-half of the solution is heated to boiling, chloride of barium is added; this throws down the sulphuric acid as sulphate of barium, which is collected on a filter, incinerated and weighed.

To the other half, neutralised with ammonia and then acidulated with acetic acid, a solution of oxalate of ammonia is added, whereby the lime is precipitated as oxalate of lime, which may be collected and weighed directly or after its conversion into carbonate by incineration, or, better still, into sulphate of lime.

Various other substances have been met with, in years past, entering into the facing of teas of British fabrication. Several of these have been already referred to. Others are Dutch pink, which consists of a yellow vegetable substance in combination with chalk; Rose pink, composed of logwood in combination with carbonate of lime or chalk; carbonate of lime, and carbonate of magnesia. It is now so rare a thing to meet with the two first-named pigments that it is unnecessary to allude to them any further, while the processes for the detection and estimation of the carbonates of lime and magnesia are too well known to need any description in this place. Moreover, processes will be found given elsewhere in this work.

CHAPTER V.

COFFEE AND ITS ADULTERATIONS.

DEFINITION OF ADULTERATION.

Chicory or any other foreign vegetable or any mineral substance. THE beverage coffee consists of an infusion in boiling water of the roasted seeds of Coffea Arabica, which belongs to the natural order Rubiace, a plant indigenous in Southern Abyssinia.

Ellis gives the following description of the coffee-tree :-"This tree, when in good health and full grown, attains a height in some countries not exceeding 8 or 10 feet, but in others averaging from 15 to 20 feet. It is covered with a dark, smooth, shining, and evergreen foliage. It is sown in nurseries, transplanted when about six months old, in three years comes into full bearing, and in favourable circumstances will continue to bear for twenty years. It delights in a dry soil and warm situation; its flowers are pale, white, fragrant, and rapidly fading. Its fruit is like that of the cherry-tree, but it grows in clusters; within the fruit are the seeds or berries. On dry and elevated parts the berries are smaller and have a better flavour, but berries of all sizes improve in flavour or ripen by keeping." The seeds are separated by bruising with a heavy roller, washed, and dried, and, lastly, freed from their paperlike coating. The seeds, improperly called berries, of Arabian or Mocha coffee have a more agreeable taste and smell than those of any other coffee, and are distinguished by their yellow colour and comparative smallness and roundness. The next best coffee is from Martinique and Bourbon. The berries of the former are larger than the Arabian coffee, rounded on the ends, of a greenish colour, and usually retain the thin pellicle which comes off by the roasting. The seeds of San Domingo coffee have their two extremities pointed; those of Java or East Indian coffee are larger, and of a paler yellow; while those of Ceylon, West Indian, and Brazilian coffee possess a bluish or greenish-grey tint. The dried fruits or berries are rarely imported. Occasionally, however, the seeds contained in their endocarp, or husks, are met with in commerce. Within the last few years the important fact has been made known that the leaves possess to a certain extent many of the properties of the seed, and hence it has been proposed to employ them in this country, as has long been done in the Eastern Archipelago, and especially in Sumatra.

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Mr. Ward, resident for many years in Sumatra, states that as a beverage the natives universally prefer the leaf to the berry, giving as a reason, that it contains more of the bitter principle and is more nutritious. In the lowlands, coffee is not planted for the berry, not being sufficiently productive, but for the leaf. The people plant it round their houses for their own use. It is an undoubted fact that everywhere they prefer the leaf to the berry.'

THE COMPOSITION OF COFFEE.

The following substances have been ascertained to enter into the composition of the raw coffee-seed:-Gum, sugar, fat, resin, volatile oil or caffeone, theine, caffeic, or caffeo-tannic acid and cellulose. The subjoined quantitative analyses are by Schräder and Payen:

It will be observed that the analysis of Payen is much more complete and definite than those of Schräder; but we have considered it desirable to institute the original analyses of the raw and roasted coffeeseed given below:

Water
Cane-sugar

Raw Coffee. Roasted Coffee.

It will be seen from the above analyses that the amount of caffeine is nearly as great in the roasted as in the unroasted berry. It is possible, however, that in those cases in which the roasting is carried to a high point, and the beans are much caramelized, a more appreciable reduction in the caffeine would take place. It will be further observed that the amount of fatty matter is likewise greatest in the unroasted berry. This result, although contrary to that of other chemists, is yet only in consonance with what might have been reasonably expected, since part of the oil undoubtedly becomes broken up and chemically changed in the process of roasting. The difference in the amount of oil obtained by Von Bibra and other analysts is so great that he was led to the very strange conclusion that the oil was formed in some mysterious manner in the act of roasting; but the real explanation lies in the tough and horny character of the unroasted bean itself, rendering it almost impossible to reduce it to the fine powder necessary to ensure the extraction of all the fatty matter by means of ether. This difficulty we have succeeded in overcoming by rasping the dried berries with a fine file. In this way we obtained an almost impalpable powder, which, however, should be completely dried before adding the ether.

According to Stenhouse, coffee beans contain about 12 per cent. of fat. Von Bibra obtained from roasted Mocha coffee 8.8 and 9.3 per cent., and from Java coffee 8.9 to 9.2 per cent. of oil.

We append a table of estimations of fatty matter in coffee made by ourselves:

'The fat extracted by ether has the consistency of cocoa-butter, and exhales the peculiar aroma of coffee, which appears to be produced from the volatile oil of the raw beans by roasting; by boiling the fat with water the aroma is driven off. The fat is a mixture of several glycerides, some of which are likewise soluble in alcohol. It appears to contain olein and palmitin, together with resin and some hydrocarbon, perhaps also other bodies. The ethereal extract likewise contains the whole of the free caffeine, and a body which colours iron salts greenish, precipitates lead salts, and reduces gold and silver salts' (Watts).

Messrs. Graham, Stenhouse, and Campbell state that raw coffee contains as much as from 6 to 7 per cent. of cane-sugar. We have found over 8 per cent. This is either entirely destroyed in the roasting, or it rarely exceeds 1.12 per cent. The same authorities give the nitrogen in roasted coffee as ranging between 2.5 and 3 per cent. Watts gives