liquor is found in the receiver, which being neutralized with potash, and redistilled, affords a liquid of specific gravity 0.911, possessed of a peculiar pungent spicy odour, and resembling coal-oil in being immiscible with water. Here are sufficient proofs that real wood-spirit can furnish with sulphuric acid nothing in any respect resembling ether.

In the course of the above and other elaborate researches, unnecessary to be detailed here, I had the good fortune to contrive a mode of solving the following rather puzzling problem – one of great consequence in this fiscal question:

Given a mixture of wood-naphtha and alcohol, each of the same specific gravity or otherwise, and which suffer no change of density by admixture: to determine in the course of twenty minutes the proportion of each.

The solution of this problem is quite independent of the boiling temperature, which is, indeed, not precise enough to lead to correct results in the present case. It is, in fact, performed without the aid of heat.

Having terminated for the present the chemical proofs, I shall subjoin some commercial considerations upon the subject. Wood-naphtha is the product of pyroligneous acid solely, from which it is obtainable in the very small proportion of less than one per cent. But that acid is made almost solely for the use of calico-printers, so that where there are no great calicoprinting establishments, as there are none in the United States, little or no wood vinegar is prepared. Now the cargo of the present naphtha detained at Liverpool, amounting to about 2000 gallons, would be equivalent to at least 200,000 gallons of pyroligneous acid, a quantity certainly far greater than has been formed there since the days of Elizabeth. Great Britain and France supply the American females with a profusion of printed goods of such price, beauty, and fashion, as to suppress almost entirely their small homely fabrics of the kind. If they cannot, therefore, send us naphtha, which they do not make, and could not make so cheaply as in the works of Swansea and other parts of Wales, they can inundate England with their coarse ardent spirits in the depressed state of their distilleries, at the rate of one shilling per gallon, whereas, naphtha is worth six times that sum; and they can readily procure as much pyroligneous acid as will suffice to give their alcohol such a taste and flavour as to deceive chemists who take their nose for their guide. This is 'the heart of the mystery.'

Dr. Ure, after the conclusion of his paper, exhibited the apparatus and explained the process for the preparation of ether, according to Boullay's continuous process.

The Chairman expressed the thanks of the Society to Dr. Ure

for his paper, and was glad that it had come forward at that time, as it afforded a demonstration of the disposition which prevails in the Society to protect the revenue of the country, notwithstanding the persecution the members have lately suffered for selling spirit in small quantities. He took occasion to caution the members of the Society against purchasing any spirit or naphtha, if offered below the market-price, which circumstance alone would be sufficient to excite suspicion. It would be foreign to the business of the meeting to discuss the sale of spirits of wine, but he might be allowed to recommend the members to be particularly careful not to sell it under any circumstances, except for medicinal purposes.

ON CAFFEINE, THEINE, THEOBROMINE, &c. THEIR CHEMICAL CHARACTERS, AND PROBABLE PHYSIOLOGICAL ACTION.

BY ALFRED BARING GARROD, ESQ., M.B.
Associate of the Chemical Society.

WITHIN the last few years, peculiar azotized substances, neutral in most of their properties, and having a remarkable com position, have been found in coffee, tea, the cocoa plant, and in some other vegetable bodies. The discovery of these did not excite much interest at the time, and their action on the body was supposed to be little or nothing, as they do not give to the alimentary substances, from which they are derived, their peculiar properties; but very recently, since the publication of the Animal Chemistry and Physiology by Professor Liebig, they have acquired great interest, for he has endeavoured to show,. that probably man, in a state of civilization, may require such substances to assist in the formation of a secretion most important to animal life-the bile.

I shall, therefore, this evening, give you an account of these substances, including their mode of preparation, and their chemical and physical properties, and then endeavour to illustrate, by comparing their composition with that of the bile, how they may prove of use in the animal economy.

1. Caffeine. This substance was discovered by Runge in 1820. Coffee contains, besides this peculiar body, many other soluble substances, as sugar, a peculiar acid called the tannin of coffee, another acid named the caffeic or caffic acid, also colouring and extractive matters, and a little volatile oil. To obtain caffeine, several methods have been employed; perhaps, the best is to precipitate the tannin and caffeic acid by means of the subacetate of lead, from a strong decoction of raw coffee, then to digest it on freshly precipitated oxide of lead, which neutralizes any acetic acid which is set free, and causes a still further precipitate after

the subacetate has ceased to do so. Any lead remaining is to be thrown down by passing sulphuretted hydrogen through the solution, and the filtered fluid by evaporation gives beautiful crystals of caffeine, which, if coloured, can be obtained quite pure by a second crystallization and the use of a little animal charcoal.

Another mode of preparation is that of Robiquet, who precipitates the decoction of coffee by means of an infusion of nutgalls, dissolving the precipitate in alcohol, then mixing the solution with magnesia, which combines and forms an insoluble compound with the tannic acid, and leaves the caffeine in solution, from which it is obtained by evaporation. The first of these methods is preferable in this country, because it does not require the use of alcohol.

Caffeine was at first considered to be a vegetable alkali, but it is found to possess neither basic nor acid properties, its solution does not affect either red or blue litmus paper; it is not very soluble in cold water; one part of caffeine requires fifty parts of water to dissolve it, neither is it very soluble in cold alcohol, but hot water dissolves it very readily, from which it crystallizes during the cooling; acids do not alter it, but cause it to dissolve more easily than water. Its solution has a slight bitter taste. It is not precipitated by the salts of iron, copper or lead, but is precipitated by tannin.

Caffeine crystallizes in two forms, from a strong and acid solution in snow white delicate 'flexible needles, having a silky lustre, not unlike asbestos, but from a weak and slightly ammoniacal solution, it crystallizes in long transparent prisms, not very flexible. When heated above 212° Fahr. it loses about eight per cent. of water, and becomes opaque; at 352° Fahr. it fuses, and at a higher temperature sublimes, without leaving any residue, in needles similar in appearance to benzoic acid. The sublimed caffeine is anhydrous. The composition of caffeine deduced from the analyses of Pfaff, Liebig, and Wöhler, is Ca N2 H2 O2.

5

In the preparation of caffeine by means of the subacetate of lead, an abundant precipitate is formed, consisting of the caffeic acid and the tannin of coffee in combination with lead. When this precipitate is washed, and suspended in water, and a stream of sulphuretted hydrogen passed through till all the lead is precipitated, and the fluid filtered and evaporated, we obtain a gummy looking mass, which consists of caffeic acid, caffeates of lime, magnesia, &c. and the tannin of coffee. To separate

*Caffeine, by the action of caustic alkalies, is resolved into carbonic acid, formic acid and ammonia. With sulphuric and hydrochloric acids it forms crystallizable compounds. The action of fuming nitric acid and heat upon it, will be spoken of under theine.

these, we should digest the mass in cold alcohol, which dissolves out the tannin of coffee, and leaves the caffeic acid and caffeates. Boiling water separates the caffeic acid from the caffeates, which are insoluble.

Caffeic acid reddens strongly litmus paper: when decomposed by dry distillation, it gives out the odour of roasted coffee. Caffeic acid does not alter the colour of the salts of iron, it precipitates lime and barytes water; the precipitates are soluble in nitric acid. Caffeic acid colours the salts of copper green, and causes a dark green precipitate. The composition of caffeic acid has not been accurately determined, but it is composed of carbon, hydrogen, and oxygen, without any nitrogen.

Tannin of Coffee obtained by evaporating the alcohol, which has been digested on the tanno-caffeic acid described above, forms a brown mass, soluble in water and alcohol in all proportions; it colours the salts of iron green; it is converted by nitric acid into oxalic acid.

Roasted Coffee.-Coffee, by being roasted, loses weight, about 20 parts in 112; but this is chiefly water. The caffeine does not appear to be volatilized or altered, for it can be obtained from roasted coffee. In an experiment made for the purpose of determining the amount of caffeine in raw and roasted coffee-the same kind of coffee being used, I found that the roasted contained about one-sixth more than the raw. This might be accounted for by the loss of water in the roasting; but it is difficult to ascertain the exact quantity by the method used, from the sugar contained in the solution preventing the crystallization of the last portions of caffeine.

In the roasting of coffee, the caffeic acid and tannin appear to be altered, and the caffeine remains unchanged. The precipitate formed by the action of subacetate of lead in a decoction of roasted coffee, is of a dirty brown colour, instead of a bright yellow, such as is obtained from the decoction of raw coffee.

Tea. There has been found in all kinds of tea a crystallizable substance, discovered by Oudry, called Theine, which has since been found to be identical with caffeine.

Besides this theine or caffeine, tea contains a great number of substances, as volatile oil, a species of tannin, gum, resin, chlorophylle, &c. The volatile oil exists in greatest quantity in the green teas, it has a very powerful odour; it becomes converted into a resin by the action of the oxygen of the air.

Theine.-To obtain it from tea several methods have been employed. It can be obtained by a similar method to that described for preparing caffeine, viz, precipitating the decoction with subacetate of lead, removing excess of lead by sulphuretted hydrogen, and then evaporating the filtered fluid, when crystals

of theine are formed, in fine needles or in prisms, according to the state of the fluid, as to dilution, acidity, &c. Dr. Stenhouse has prepared theine by a different process, founded on the volatile property of theine: he adds acetate of lead to a strong decoction of tea, evaporates to dryness, and then sublimes from a metal bath. The theine is then obtained in feathery crystals, like snow, anhydrous.

Tea-leaves dried, powdered, mixed with sand, and then heated on a bath, afford crystals of theine, without any preparation; but the heat must be carefully regulated, or an oily pyrogenous body is formed, which dissolves the theine.

The green teas do not contain so much theine as the black; the average proportion is about one per cent. In some extract of tea from China, given to me by Dr. A. T. Thomson, the quantity of theine was very large.

Now, it has been found that theine is identical with caffeine, and, therefore, the description of the properties of caffeine applies equally to theine. A test for theine or caffeine has been proposed by Dr. Stenhouse, which is the following:

Heat quickly a portion of theine, with two or three times its weight of fuming nitric acid, nearly to dryness, and to the yellow substance formed add a drop or so of ammonia, an intense purple colour is produced; so the test is the same as that for uric or lithic acids. It is very remarkable, that a substance having such a peculiar composition as theine or caffeine, should be found in both tea and coffee, for these plants do not belong to the same natural families. The peculiarity of their composition consists in their containing such a large amount of nitrogen; for, with the exception of urea and theobromine (a substance from cocoa to be presently described), caffeine contains more nitrogen than any other organic substance; and there is also the same ratio between the proportion of carbon and nitrogen in it, as there is in taurine, a crystallizable substance obtained from bile; but we shall speak more of this presently.

Tannin from Tea.-This is contained in the precipitate formed when the subacetate of lead is added to the decoction or infusion of tea. The tannin can be separated by passing sulphuretted hydrogen through the precipitate suspended in water. It seems to resemble the quercitanic acid; it blackens the solution of salts of iron. It seems to exist in tea in combination with the theine; and the compound is much less soluble in cold than in hot water, and this seems to cause a strong infusion of tea to become turbid when cold. More tannin is said to be contained in black than in green teas, as found by Sir H. Davy, and more recently by Dr. Stenhouse, although green teas appear from taste to be more astringent.