The amount of sugar in coffee, and in a great variety of vegetable substances, has been determined, both before and after roasting, by the process of fermentation and distillation.

The results obtained by Messrs. Graham, Stenhouse, and Campbell are given in the following tables :

SUGAR IN COFFEE BEFORE AND AFTER TORREFACTION.

The fermentation test has the advantage of being easily applied, and the results might, in combination with the microscope, prove useful in some cases. In applying the test, the process described on page 49, under the head of "Analysis," is followed.

The determination of the sugar by the copper test is more tedious than by the fermentation test; but at the same time it is not open to some of the objections which may be urged against the other. In estimating the sugar by this method, 200 grains of the coffee are exhausted with hot water to the extract is added basic acetate of lead, so long as a precipitate appears. The extract is then filtered and the precipitate washed with hot water. The filtrate is next treated with sulphuretted hydrogen, and again filtered and the lead precipitate washed. The solution is now boiled to expel sulphuretted hydrogen, and tested for glucose with a standard solution of copper, as described on page 106.

There are some cases in which the character of the ash affords evidence of adulteration. The ash of coffee is distinguished by the absence of soda, and also by the extremely small proportion of silica it contains, the amount of which varies from o'17 to 0.45 per cent. On the other hand, the amount of silica or sand in the ash of chicory and dandelion varies from 10'69 to 35.85 per cent.; barley, from 173 to 32'7; oats, from 37.82 to 50 28; and rye, from o'69 to 146. Thus it is sometimes practicable to obtain valuable information without making a formal analysis of the ash, by simply digesting it in hydrochloric acid, and observing the character and quantity of what remains insoluble. The presence of 1 per cent, or upwards of silica in the ash of a sample is sufficient to raise a suspicion of adulteration. It is not often that an analysis of the ash of a suspected sample is resorted to in practice; it is a tedious operation, and would only be performed with the view of confirming the results obtained by some of the other methods of examination to which reference has been made.

The following table, which is taken from the Coffee Report by Messrs. Graham, Stenhouse, and Campbell, exhibits a complete analysis of the ash of four kinds of chicory, also of lupins, acorns, maize, parsnips, and dandelion root.

ANALYSES OF CHICORY AND CERTAIN SEEDS AND ROOTS.*

Chicory, deducting Sand

and Silica.

Deducting Silica, etc.

Not deducting Silica, etc.

Potash

Soda

38 53 27 85 46 07 46 27 33 83 55 49 31 28 56 86 20 22 33 54 54 93 30 74 56 54 17.95 9'34 16.90 3'17 5'49 17'90 0.63

Acid
Phosphoric
Acid
Silica, etc...
Sand

34 87 17'75 063 30'95 7·81 6·98 311 6.88 12.87 775 601 306 6·851143 6:23 436 14'98 652 147 618 4 32 1472 649 131

204 322 436 460 0'56 13.82

12*27 12 61 11:00 9:59 25'74 11 26 45°29 1391 12.63 25 53 11 15 44 50 13 84 11 21 381 261 1275 10'52

...

0.87 1'01 178 0'57 11 26

The relative solubility in ether of coffee and a variety of vegetable substances used to adulterate it, may, in some cases, be found useful as a confirmatory test for indicating the character and the proportion in which the adulterating substance is present. Coffee yields much more soluble matter to ether than do sweet roots, cereals, and leguminous seeds generally. Thus roasted coffee, when agitated four times successively in ten times its weight

* These Analyses, and also those on p. 46, were made by the Author for the Coffee Report.

of ether, gives from 14'79 to 15'10 per cent. of oil and resin, including a small proportion of caffeine. Roasted chicory, when similarly treated, gives 7'72 per cent. of extract. Roasted maize gives 4.30 per cent., and roasted beans 157 per cent. The deficiency of fat in the sweet roots and other vegetable substances is frequently made up in the roasting by the addition of American or Australian tallow to prevent burning, and in applying the ether test it is therefore necessary to guard against being misled by the presence of a small proportion of foreign fat.

Venetian Red or Oxide of Iron.—It is very rare, as already stated, that any mineral matter such as oxide of iron is now employed to give colour or weight to coffee. The oxide is usually in such a fine state of division that it cannot be seen by the naked eye, or be detected and identified by the microscope. When the presence of such a compound is suspected it is necessary to burn a given weight of the coffee and observe whether the ash is of a deep red or yellowish-brown colour, and if so it is probable that oxide of iron has been added, and it will be necessary to determine the amount of iron in the ash and compare the result with the quantity found in genuine coffee, or the proportion that may be present in mixtures of chicory and coffee.

Burnt Sugar.-When a sample of coffee which is free from roots and other foreign vegetable substances, imparts to water a deep and rapid colouration, there is reason to suspect that burnt sugar has been added. The black shining particles of the caramel can usually be distinguished by the naked eye from the dull light brown fragments of coffee, and be removed for examination. The solution of the separate particles in water, and the high colour they impart to it, are indicative of burnt sugar.

When all other forms of adulteration have been disproved, it will be necessary to resort to the estimation of the glucose in the coffee, and to the specific gravity test for the proportion of burnt sugar present. As burnt sugar nearly always contains a considerable proportion of glucose, the detection of any appreciable

percentage of such sugar by the copper test would be confirmatory of the presence of caramel.

MICROSCOPIC EXAMINATION.

In the detection of the adulterants of coffee, the aid of the microscope is always resorted to. It becomes, therefore, a matter of great importance to gain some clear knowledge of the structure of the tissues of roasted coffee, and also of the various substances which are likely to be employed in its sophistication.

In coming to a decision as to the kind of adulterant which may be present in coffee, or any other article in which the microscope is relied upon for detecting the presence of a foreign substance, it is not enough, usually, to trust to any mere drawing or representation of the adulterant indicated. It is always advisable to examine under like conditions a portion of the particular seed or root which it is supposed has been added, and when the percentage is required, to make up mixtures representing different degrees of adulteration, and to judge, from the number of foreign particles on the slide, the extent to which they have been added to the pure coffee or other article.

In some instances where a foreign substance is shown to be present by the microscope, and it is possible to identify it, the knowledge thus obtained becomes of the utmost value in indicating the particular chemical and other tests which should be applied in order to determine the proportion in which the adulterant is present.

I. ROOTS.

All the roots that can be employed with advantage for mixing with coffee are very similar in structure. They mainly consist of a mass of cells, among which occur bundles of jointed tubes, the sides of which present the appearance of being marked with bars or pits.