the air is a proof, that the coffee has lost some of its most volatile parts; and as that liquor is found to have lost its peculiar flavour, and also its exhilarating quality, it is inferred, that both these qualities must undoubtedly depend on the preservation of those volatile parts which so readily escape.

If the liquid were perfectly at rest, the particles which could escape from its surface, would be incomparably less in quantity, than would escape by agitation, which would continually present new portions of the fluid to the air. But all fluids, while heating or cooling, by partial communication, are known to be agitated; a fact long and well known, but particularly explained and insisted upon by our author, in many of his valuable works, and which he again perspicuously and familiarly explains in the present essay. His object is to indicate by what means the heat of the liquor may be uniformly kept up in all its parts for the consequence being, that the parts will, in those circumstances, be at rest, the motions by which the aromatic parts might have been dissipated, will not take place.

:

"By pouring boiling water on the coffee, and surrounding the containing vessel with boiling water or with the steam of boiling water, the coffee itself will be kept permanently at the same heat, and will not circulate, or be agitated.

"The count observes, that from the well-known fact, that boiling water is not the most favourable for extracting the saccharine parts from malt in brewing, he was induced to try a lower temperature than the boiling heat in making coffee; but the coffee did not prove so good. The cold infusion of coffee, which

he also tried, was of very inferior quality.

"The common method of boiling coffee in a coffee pot, is neither economical nor judicious. A large quantity of the material is wasted in this method, and more than half of the aromatic parts, so essential to its good qualities, are lost.

One pound of good Mocha coffee, which, when properly roasted and ground, weighs only fourteen ounces, will make, by proper management, fifty-six full cups of the very best coffee that can be made.

"If it be not ground finely, the surfaces of the particles only will be acted upon by the hot water, and the waste will be very great, from the large proportion of coffee left in the grounds.

"The size of a coffee cup in England usually answers to 8 cubic inches, but the count considers the gill measure as a proper standard for a cup of coffee, which he therefore adopts. This will fill the former cup to seven-eighths of its capacity, and a quarter of an ounce of ground coffee will be fully sufficient to make a gill of the most excellent coffee.

"It is well known to chemists, that any solvent already in part charged with a substance intended to be taken up, will be less disposed than before to take up any additional quantity; and upon this is founded the process of percolation or straining, as is practised in brewing and other arts, and has been for some time recommended and used in making coffee. To this the count gives this approbation. He finds, by experience, that the stratum of ground coffee to be laid upon a perforated metallic bottom of a vessel or strainer, ought to be about twothirds of an inch thick, and to be $2

reduced

=

=

1educed by pressure by a piston or flat plate of metal (after levelling it) to less than half an inch. From the data he infers, by a chain of observations, that if the height of a cylindrical vessel or strainer be taken constantly at 5 inches, the diameter of its bottom must be To make 1 cup of coffee 1 inch 2 cups 2-3 or 4 cups = 2 -5 or 634-7 or 84-9 or 10 = 43-11 or 12 = 5. "These strainers are to be suspended in their reservoirs or vessels for containing the coffee, and the whole included in another vessel called the boiler, which is to contain boiling water, kept hot by a lamp, or otherwise. The forms of these are given with drawings, upon which it does not seem needful to enlarge in the present abridgment, because there are several vessels of this description, with the exception of the surrounding boiler, to be found in our shops.

"The reader must have recourse to the essay itself for these and other particulars of considerable interest, and delivered in the familiar and perspicuous style which distinguishes the writings of this author. The poor, and those who prefer simplicity of structure to the extremes of perfection, will be gratified by a description of his last apparatus, fig. 8 It is a porcelain, or earthen jug, with a tubular spout, not unlike those which we call milk jugs, except that these commonly have a lip-spout (which would answer nearly as well). Into the mouth of this is fitted a tin vessel, which fits and descends a little way down. It has a flat bottom perforated with many holes, and a good close cover ¿

and it would be well to have a round plate or rammer, to compress the coffee on its bottom, and defend it from the stream of hot water, when poured in. These several parts are to be dipped in boiling water before using, and the difference between coffee made by this simple and cheap apparatus, of which the mug may also be applied to other uses, and that made by the most perfect, machines, will scarcely be distinguishable.

"Sufficient length has already been given to our abstract, to forbid us to follow the count in the explanation of his views directed to the benefit of society, with relation to the comforts of individuals, as well as to the economy of the political aggregate. That it would be preferable to consume an article produced by the colonies of European nations, who demand the manufactures and products of the parent state, instead of sending bullion to China for an article of less value: that it would be preferable that the poor should enjoy the innocent exhilaration of coffee, and the nutriment of sugar, instead of forgetting their hardships during the momen tary intervals of insanity, produced by fermented and distilled liquors; that they should be cheerful, benevolent, animated, healthy, and industrious with coffee, instead of becoming outrageous, mischievous, diseased, idle, and sunk in languor and debility with gin, &c. &c. are among the meditations interspersed through this little work, which the reader will be gratified in consulting, and will probably be induced to make others in his turn.

hese

ON

colour. If nitric or sulphuric acid have been employed, the prussiate of lime will show this by staining the paper blue, but it cannot produce the writing.

"Hidroguretted sulphurets of the alkalis, or of the alkaline earths, are very prompt and powerful tests of ferruginous salts. The alkali, or earth, combines with the acid; and the sulphuretted hidrogen with the oxide of iron, forming an hidroguretted sulphuret of iron. Iron in the state of red oxide is partly disoxidated by the hidrogen, water is formed, and the iron passes to the state of black oxide. This is the case with writing turned rusty: these re-agents immediately change it to a green black, much deeper than gallic acid would give. A solution of sulphate of iron mixed with an bidroguretted sulphuret produces a very deep green black ink.

"The same attractions are exerted when the hidroguretted tests are applied where writing has been obliterated by the oxalic acidule or the oximuriatic or nitric acid. If the oxalic acidule were employed, the characters will reappear of a green black or brown red. If the oximuriatic acid, of a green black or pale rust colour. The less the revived writing approaches a black, the more the iron was oxided in the metallic salt decomposed, or the less the iron was disoxided by hidrogen. The writing on which nitric acid has acted strongly cannot be reproduced: but on passing sulphuretted hidrogen over the paper where it was, waving lines of a green black will be formed on the remotest parts to which the sulphuretted hidrogen penetrates. These lines may be produced in great number, and in different

directions. They are owing to the sulphuretted hidrogen con.bining with the oxide of the ferruginous nitrate. If the undulating lines, or the letters that have been restored, should disappear, they may be reproduced by dipping the paper into cold water. Beside the traces of writing, and the undulating lines just mentioned, the paper takes a yellow colour when it is not impregnated with an acid, and a green more or less deep when it is. The green colour will be deeper, in proportion as the acid was stronger, or in larger quantity. In all cases the paper retains the colour of fresh butter after it is dry. The hidroguretted sulphurets should be diluted with half or two thirds their quantity of water before they are used, as in their ordinary state they are too strong.

"From what has been said, we may hope to restore writing, that has been obliterated by any agent except the nitric acid and if this have been employed only in small quantity, without the assistance of any other acid, and its action has not been too long continued, on holding the paper to the fire the writing will reappear of a rust colour.

"With regard to the improvement of ink, little progress has been made since the time of Lewis. Inks made by infusion, and with green sulphate of iron, are of a Prussian blue colour, light, pale when written with, but growing black as they dry on the paper. Those made by decoction are blacker, thicker, and form a more copious sediment, which is of a dirty Prussian blue colour. Decoction extracts from galls all the soluble parts; infusion takes up chiefly the gallic acid, and muci

lage,

lage, with a little extract and tannin. In the decoction the iron of the green sulphate becomes more oxided, and the extract and tannin acquire oxigen, by absorption from the atmosphere; and the iron in a higher state of oxidation, and the oxigenized extract, produce a deeper black with the gallic acid and tannin. The more abundant sediment is owing to a larger quantity of extract and tannate of iron. In inks made by infusion, the oxide of iron, extract, and tannin, increase their oxigenation very little, till they come to dry on paper. Nitric acid immediately obliterates writing with ink made by infusion, but that which has been made by decoction resists its action much longer, on account of the larger quantity of extract in it.

"In proportion as the infusion or decoction of galls grows old, its surface is covered with mother, which is the mucilaginous principle separated. This mother ceases to form in about a year, during which the pellicle produced on the surface should be removed three or four times. The infusion or decoction of galls grows brown as it becomes oxigenized, takes an amber colour, and emits a pleasing smell; and, when combined with green sulphate of iron, no longer produces a Prossian blue, but a green black. The amber colour of this infusion or decoction is owing to the oxigenized extract and tannin. The green colour of the ink arises from the mixture of the black of the gallate of iron with the fawn colour of the oxigenized tannin, which in this state can no longer combine with the oxide of iron. If the tannin be separated from the infusion or decoction by means of an alkali, the green or red sulphate of iron

forms with it a very black and purer ink; and the alkali in the solution facilitates the union of the oxide of iron with the gallic acid, by combining with the sulphuric acid of the sulphate. The oxigenized extract concurs in rendering the ink blacker, as does the oxide of iron more highly oxided.

" Infusion of galls is preferable to the decoction, âs it dissolves the principle, that is essential to the composition, and very little of those that are foreign to it. Logwood browns the ink, and loads it with its colour; it is better therefore, to use in its stead a small quantity of galls in addition to that directed by Lewis. The following is the composition of a good ink.

"Infuse in one litre (a wine quart] of rain or river water 125 gram. [4 oz. troy] of bruised galls, letting them stand in the sun four hours in summer, or six hours in winter. This infusion may be used immediately after straining; but it is better to let it stand four or six months, removing the mother that forms on the top now and then, and finally separating by filtration both this and the tannin that has fallen to the bottom. In this dissolve 32 gr. [a troy ounce] of pow dered gum arabic; then add the same weight of finely powdered sulphate of iron, superoxigenized by calcining it till it grows reddish; and continue shaking the mixture till this is completely dissolved. The ink thus made is fine, light, and of a purple tinge, but black when dried on the paper. It is nearly, if not precisely, the composition of Guyot's ink.

"Dr. Tarry next proceeds to his indelible ink, the composition of which however he does not disclose. He says only, that it contains neither

galls,