(f.) A substance derived from the malt, becoming dark-brown on the addition of sulphuric acid.

(3.) Chloroform extracts (a.), (b.), and (e.), and also (f.), a substance partly precipitated by potassium iodide and phosphomolybdic acid;

(g.) A substance reducing ammoniacal solution of silver nitrate;

(h.) A substance crystallisable from ether. All of these are derived from the malt.

The normal reactions of the substances being known, the following scheme will be found useful, always bearing in mind that few chemists, should they obtain any of the reactions mentioned, would conclude from this alone that the substance is actually present. The reaction would be considered as an indication only, to be supplemented by other evidence. Unless this is remembered and acted upon, the most unfortunate errors may be committed by the inexperienced. The beer is most conveniently shaken up with the solvent in the tube figured p. 69; the ether and benzine will float at the top, the chloroform will gravitate to the bottom; in either case separation is tolerably easy. It will, however, be found a good plan, in the first place, to separate the liquids rather roughly--i.e., to draw off the ether, benzine, and chloroform layers, with some of the adjacent liquid, to wash this in the same tube with water, to withdraw the solvent from the water as completely as possible by the separating tube; and if this (as sometimes happens) is not very feasible, to evaporate the impure liquid to dryness in a water-bath, and exhaust the residue with the original solvent. The latter may be, in the first place, concentrated over hot water, and then portions distributed between two or three watch-glasses, and evaporated to dryness.

I. THE ACID SOLUTION.

PETROLEUM RESIDUE.

(a.) It is amorphous, colours sulphuric acid first brown, then violet, and finally red violet. Traces of Absynthin. (b.) It is amorphous, colourless, having a hot taste, reddening the skin, and colouring sulphuric acid brownish-red. Traces of Capsicin.

(c.) It is amorphous, green, is coloured by sulphuric acid and sugar, and gives no precipitate with ammoniacal silver solution.

Resin of the Juniper berries.

(d.) It is crystalline, yellow, and becomes blood-red on warming with cyanide of potassium.

Picric acid.

BENZINE RESIDUE.

A. Crystalline residue.

It is not bitter; caustic potash colours it purple-red, sulphuric acid first red, then orange. Aloetin.

B. Amorphous residue.

a. The residue soluble in water; does not trouble or reduce gold chloride solution in the cold.

(a.) Tannin does not precipitate the solution in water; residue sharp tasting.

1. Sulphuric acid colours it red brown.

2. Sulphuric acid colours it brown.

Capsicin. Daphne bitter.

(b.) Tannin precipitates the solution in water; the residue somewhat bitter.

I. Basic lead acetate causes a weak turbidity, sulphuric acid and sugar scarcely redden.

1. Iron chloride colours the watery solution, on warming, brownish-
green; taste slightly bitter.
Gentian bitter.

2. Iron chloride colours the watery solution brown; taste peculiar,
almost unsupportably bitter.
Quassiin.

II. Basic lead acetate strongly precipitates, sulphuric acid and sugar colour it gradually a beautiful cherry-red; taste bitterish.

Cnicin. b. The residue soluble in water; does not trouble solution of gold chloride in the cold, but reduces it on warming.

(a.) Tannin causes a faint turbidity in the watery solution, ammoniacal silver solution is not reduced. Heated with diluted sulphuric acid, an ericinol smell is developed. Fröhde's reagent colours it blackbrown, sulphuric acid and sugar a beautiful red. Ledum bitter.

Trifolium bitter.

(b.) Tannin precipitates the watery solution; ammoniacal solution of silver is reduced. Heated with diluted sulphuric acid, a weak smell of menyanthol is developed. c. The residue soluble in water, precipitates in the cold chloride of gold, but does not reduce it upon warming. Heated with diluted sulphuric acid (1 of acid to 5 of water), it gives a weak benzoic acid smell.

Centaurea bitter. d. The residue soluble in water, precipitates in the cold chloride of gold, which it reduces upon warming. Sulphuric acid dissolves it first brown, then gradually violet; after the addition of water quickly a beautiful violet. Hydrochloric acid of 1·135 specific gravity colours it first green, then a beautiful blue.

CHLOROFORM RESIDUE.

A. Chloride of gold does not precipitate, and is not reduced.

Absynthin.

a. Tannin gives no precipitate; the residue has a pungent taste. Sulphuric acid colours it dark-brown red; it reddens the skin.

b. Tannin precipitates.

Capsicin.

(a.) Basic lead acetate gives a decided precipitate. Heated with diluted sulphuric acid it is first troubled, then it becomes brownred, and develops a weak smell of benzoic acid.

Cnicin.

(b.) Basic acetate of lead gives little or no precipitate.

I. Sulphuric acid colours brown.

1. Residue bitter.

aa. Strongly bitter.

bb. Residue somewhat bitter.

2. Residue tasting pungent.

Quassiin. Gentian bitter.

Daphne bitter.

II. Sulphuric acid colours but slightly yellow or not at all.

Colocynth bitter.

B. Chloride of gold does not precipitate in the cold, but is reduced in the warm.

a. Tannin does not precipitate.

1. Intoxicates fish, tastes bitter.

Picrotoxin.

2. Is tasteless or slightly bitter; caustic potash colours it red-brown. Constituent of Aloes.

b. Tannin precipitates. (a.) Ammoniacal solution of silver is reduced. Heated with dilute sulphuric acid, as well as with Fröhde's reagent, there is a strong smell of menyanthol. Menyanthin.

(b.) Ammoniacal solution of silver is not reduced. With concentrated sulphuric acid and sugar, after long standing, a splendid carmine red develops; heated with diluted sulphuric acid, as well as with Fröhde's reagent, an intense cricolin smell is developed. Ericolin. C. Chloride of gold precipitates in the cold, and is not reduced by the application of heat. Nitric acid colours violet. Colchicine.

Heated with sulphuric acid, an odour somewhat like trifolium is developed, then the solution becomes red-brown, and the smell similar to benzoic acid. Centaurea bitter.

D. Chloride of gold precipitates in the cold and reduces in the warm. Sulphuric acid colours brown, then the solution becomes gradually dirty violet. Wormwood bitter.

If necessary to go further, search may be made for the alkaloids by rendering the liquid weakly alkaline by carbonate of soda or by ammonia:

II. THE ALKALINE SOLUTION.

I. RESIDUE OBTAINED BY SHAKING UP WITH BENZINE.

(1.) It dilates the pupil.

(a.) Platin chloride does not precipitate the aqueous solution. A solution in sulphuric acid gives on warming a peculiar smell.

(b.) Platin chloride precipitates.

Atropine. Hyoscyamin.

(2.) It does not dilate the pupil.

(a.) The sulphuric acid solution gives with oxide of cerium or bichromate of potash a blue colour.

Strychnine.

(b.) The sulphuric acid solution gives a red colour with nitric acid solution. Brucine.

II. RESIDUE OBTAINED FROM SHAKING IT UP WITH AMYLIC ALCOHOL. (This need only be done if salicin be suspected.) On warming with sulphuric acid and bichromate of potash, a smell of salicylic acid is developed. Salicin.

§ 269. Dr. Adams* has found that the bitter of new hops is destroyed by boiling with dilute sulphuric acid. He operates as follows:-The beer is boiled, and basic lead acetate solution added until on the point of saturation. The boiling is continued for some time, after which the precipitate is filtered off and the filtrate is acidified with sulphuric acid and filtered from the lead sulphate; the clear acid filtrate is concentrated to a small bulk, chalk is added to neutralise the acid, and the liquid again filtered. The filtrate is now devoid of bitter taste, if hops alone have been used.

A second process suitable for detecting either old hops or new is on the same principles. The boiling beer is neutralised by barium hydrate, or, rather, made alkaline. To the filtrate sulphuric acid is added until made just acid. Then the lead treatment as in the first process is followed, and a filtrate ultimately obtained devoid of bitterness, if hops alone have been used. On the other hand, most bitters, such as quassia, gentian, chiretta, and many others, are but little affected by the boiling with sulphuric acid.

A very good process, only aiming at the identification of a few principles, is recommended by Enders; it is as follows:

The beer is evaporated to a syrup, the dextrin separated by mixing it with three or four times its volume of alcohol, the liquid filtered, and the sugar precipitated by ether. The filtered ether-alcohol solution is evaporated, the residue dissolved in alcohol, mixed with water, and precipitated by means of acetate of lead. The precipitate is filtered, the filtrate put on one side. The washed precipitate is then separated from lead by SH, the lead sulphide filtered and washed with alcohol, and the filtrate (as well as the alcohol washing of lead sulphide) evaporated together. The residue is dissolved in chloroform, and the solution warmed with water until all the chloroform is driven off. The hop bitter, which remains insoluble, is filtered off, and the filtrate evaporated to dryness. The lupulin in it should taste bitter and have an acid reaction; it is soluble in alcohol, ether, and chloroform; is not precipitated when in solution in weak

*Analyst, July, 1890.

spirit by tannic acid, but is precipitated by acetate of lead. Ammoniacal solution of silver is not reduced by it. The filtrate of the first lead precipitate is freed from lead by SH2, the lead sulphide filtered off and washed with hot water, the excess of SH, driven off by warming, and then tannin added to the filtrate. If no precipitate occurs, absynthin, quassiin, and menyanthin are absent. Any precipitate is filtered, dried with carbonate of lead, boiled with alcohol, evaporated, and, lastly, treated with ether. The latter agent dissolves absynthin, which is also soluble in alcohol, and in much hot water; from the latter solution it is precipitated by tannic acid, but not by lead acetate; it is soluble in sulphuric acid, and on careful addition of water to this solution a violet-blue colour is produced. Absynthin reduces an ammoniacal solution of silver. Ether leaves menyanthin and quassiin undissolved. Both are soluble in alcohol, and the latter behaves towards tannic acid and acetate of lead like absynthin. Menyanthin reduces ammoniacal solution of silver; quassiin does

not.

Picrotoxin may be specially tested for by some one of the following processes:

Herapath's Process.-Mix the beer with acetate of lead in excess; filter, and transmit sulphuretted hydrogen through the filtrate. Filter again, concentrate the filtrate, and treat it with animal charcoal, which has the property of absorbing the picrotoxin. Wash the animal charcoal, dry at 100°, and boil with alcohol; this dissolves out the picrotoxin, from which it may be obtained in tufts of crystals.

Depaire's Process.-Mix with 1 litre of beer finely powdered rock salt (which throws down the resinous and extractive matters), and shake the liquid with ether; an impure picrotoxin crystallises on separating the ether and evaporating it: or the beer may be simply acidulated with hydrochloric acid and agitated with ether, the ether separated and evaporated as before.

Schmidt's Process.-1. Evaporate the beer in a water-bath to a syrupy consistence, mix it with tepid water till it is perfectly liquid, so as to bring the volume to a third of the liquid used; heat and shake with animal charcoal. Let it stand several hours, filter, and heat slightly; precipitate by basic acetate of lead, and again filter. The liquid should now be of a yellow wine-colour; if not, re-filter through animal charcoal. Add from 5 to 10 cubic centimetres of amylic alcohol, and shake briskly several times at intervals; after twenty-four hours the amylic alcohol, containing the greater part of the picrotoxin, collects on the surface. The remainder is subsequently eliminated by fresh treatment with amylic alcohol. Collect the limpid layers of this alcohol, and