(c.) There is no change of colour on the addition of hydrochloric acid, &c. Heat with ammoniacal copper solution, bluish-green; confirm the presence of picric acid by the cyanide of potassium test, a blood-red colour-PICRIC ACID; the colour becomes an olive greenNAPHTHALINE YELLOW.

B. Various shades of colour from green to almost black-MADDER YELLOW, FUSTIC, FUSTET, QUERCITRON, FLAVIN, BERRIES, WELD. Boil with aluminium sulphate, with the addition of an equal volume of water; liquid becomes yellow, with a red reflection-MADDER YELLOW, with tin. Yellow, with a bluish-green reflection-FUSTIC. Liquid yellow without reflection. Heat with baryta water, a red colour-FUSTET. The colour is only darkened. Boil with glacial acetic acid. On cooling, if the liquid is yellow, or greenish-yellow-ENGLISH FLAVIN. If the solution is not at all, or only faintly, coloured, boil with basic lead acetate. This, with regard to fabrics, if a tissue is dyed with WELD, the tissue will not change colour; if with QUERCITRON or BERRIES, the tissue will change to orange-brown; but articles of food will be scarcely coloured with these substances.

GREEN COLOURS.

If the green colouring-matter is not soluble in water, it is probably chlorophyll, unless indeed it is a mineral colouring substance. Chlorophyll best recognised by the spectroscopic characters of its alcoholic solution (see p. 104). If not chlorophyll nor a mineral substance, then

A. Boil with a moderately concentrated solution of potassic cyanide. (a.) Colour changes into brown or yellow-ANILINE GREEN, GREEN, containing INDIGO-SULPHURIC ACID (carmine green).

(b.) Does not change, or changes into a brownish- or yellowish-greenGREEN, containing INDIGO with or without CARMINE GREEN. B. In any of the foregoing cases add an equal volume of water, and then a solution of aluminium sulphate until an abundant precipitate is formed; filter and wash. (Excess of the precipitate must be avoided.)

(a.) Filtrate yellow or reddish-ANILINE GREEN.

(b.) Filtrate blue-(1) precipitate colourless-CARMINE GREEN with PICRIC ACID; (2) precipitate yellow CARMINE GREEN with a vegetable yellow. Dissolve the yellow precipitate in water, add sulphuric acid, and filter: a green fluorescence-FUSTIC; no fluorescence WELD, TURMERIC. Test for turmeric in the original substance by boiling with alcohol, and adding boric and hydrofluoric acids.

(a.) Filtrate colourless, precipitate yellow-INDIGO.

(b.) Filtrate blue; if the precipitate is colourless, PICRIC ACID may be present, and should be tested for; if coloured, there is probably a vegetable colour present.

BLUE COLOURS.

Dissolve out the colouring-matter with alcohol of 80 per cent., or treat the substance itself with alcohol, allowing it to remain in the liquid, and add a few drops of hydrochloric acid: a red colour-LOGWOOD. Confirm by adding to an alcoholic solution ammonia and then alum; a blue or violet precipitate should result. If the liquid does not dissolve any of the colour, it is most probably Prussian blue, but it may also be indigo. If, on the other hand, although some of the colour is extracted, yet the substance still remains blue, it is probably ANILINE BLUE or INDIGO-SULPHURIC ACID. Add strong sulphuric acid, with INDIGO-SULPHURIC ACID, no change. The colour changes into a yellow or reddish-brown in presence of ANILINE BLUE. On heating with sodium carbonate again, INDIGO is not changed, but PRUSSIAN BLUE is changed into yellow or brown.

VIOLET AND PURPLE COLOURS.

Heat with ammonium sulphide.

A. The tissue is bleached; soluble ANILINE VIOLET, MAGENTA, with INDIGO CARMINE. These two may be distinguished by the action of boiling alcohol: SOLUBLE VIOLET remains violet, MAGENTA becomes red, the substance becomes brownish-red. Presence of MAUVE, or HOFFMAN'S VIOLET. These may be distinguished by the addition of hydrochloric acid, which colours HOFFMANN'S VIOLET yellow, but MAUVE becomes purple.

B. Turns olive brown-ALKANET. (Confirm by spectrum.)

D. Hardly any change. Presence of ARCHIL, ARCHIL with INDIGO, LOGWOOD, or MADDER.

Boil with alcohol

a. The solution is pink, and changes to violet on the addition of ammonia ARCHIL; if the ARCHIL is accompanied with INDIGO, hot chloroform will colour blue.

b. Solution in alcohol remains colourless. Heat with dilute hydrochloric acid: LOGWOOD is coloured red, and may be further identified by test already given; if INDIGO is associated with it, hot chloroform will colour blue. With hydrochloric acid, madder, if it is coloured at all, becomes yellow.

The accompanying Tables will also be found useful in the identification of organic colours.

THE MINERAL MATTERS OR "ASH" OF FOOD.

ANALYSIS OF THE ASH OF ORGANIC SUBSTANCES.

§ 65. As a general rule, testing the ash for abnormal metals and alkaline earths is necessary, and more especially if the ash present any unusual character, whether in weight, colour, or

solubility. Leaving for the present the special tests, the number and nature of the constituents which require to be determined for the purpose of the food-analyst, vary according to the particular substance under examination, e. g.

In all substances, the percentage.

In such fluids as milk, the alkaline phosphates and the chlorides. In seeds, such as wheat, cocoa, &c., the total phosphoric acid. In beer-ash, the amount of common salt.

In bread-ash, the presence or absence of alumina, magnesia, and proportion of silica to alumina.

In tea-ash, the alkalinity, the iron, the silica, and proportion of soluble to insoluble ash.

In coffee-ash, likewise the proportion of soluble to insoluble ash, but the presence or absence of silica becomes also of importance.

From these illustrations (which might be multiplied) it follows that, for the purposes of the food-analyst, the general constitution of the ash will be sufficiently known when the following determinations have been made :

(1.) The total percentage of ash.

(2.) The total percentage of ash soluble in water.
(3.) The total percentage of ash soluble in acid.
(4.) The alkalinity of the ash.

(5.) The percentage of chlorine.

(6.) The percentage of phosphoric acid.

(1.) The Total Percentage of Ash.-Of the various methods of estimating an ash, the simplest and most practical appears to be -to place a sufficient quantity of the substance to be burnt in a capacious platinum dish, and to consume at the lowest possible temperature by heating with a ring burner.* The quantity to be taken is regulated by the amount of ash in the substances. For example, flour, containing only 7 per cent. of ash, would give with 50 grms. 35 ash, which is about as small a quantity as it is possible to work with conveniently, whilst in the case of coffee, tea, and cocoa, from 5 to 20 grms. is for most purposes ample.

If the sulphuric acid in the ash is not to be determined, a wide glass tube (such as the chimney of a common paraffin lamp) adjusted over the dish, by its powerful up-draught greatly expedites the operation; but if the sulphuric acid is to be determined, the impure gas of commerce renders the results too high. It is, however, of course open to the analyst to make the gas pass through a proper absorption-apparatus, or to use as a fuel, alcohol.