the Family Cyclopædia, article Nankin Dye, in the Supplement; to Gray's Supplement to the Pharmacopoeia; and, lastly, to the Family Dyer and Scourer, by W. Tucker, where almost innumerable solutions of annatto may be found.

Whether the addition of aqua lixivum caustic-if we can find out what it is—and of alkohol, to the solution of annatto, will give the patentee an exclusive right to the vending of this nostrum, we do not pretend to say; but this patent, in sober seriousness, appears to us to be a sort of experiment upon the credulity and understanding of the age.

Inrolled, June, 1822.

To THOMAS MARTIN and CHARLES GRAFTON, of Birmingham, Warwickshire, for their Method of making fine light BLACK, of very superior colour, which, for distinction from other Blacks, they call Spirit Black. And a new Apparatus for producing the same.

THE object of producing this fine light black is principally for the manufacturing of printers' ink. The material commonly called lamp-black is a carbonaceous matter, usually prepared by burning oil or resinous substances, and collecting the sooty particles in a winding chimney. In the improved process, which forms the subject of this patent, the black is obtained by burning common coaltar, which should be divested, as much as possible, of the ammoniacal liquor and acid held in solution.

For this purpose, it is proposed that four casks should be employed, each capable of holding one hundred and thirty gallons, and into every one of them is to be put

about sixty gallons of the rough impure tar; to which an equal quantity of lime water is to be added, and then agitated by machinery or manual labour until the limewater is completely mixed with the tar. The vessels should then be suffered to rest for about six hours, by which time the tar will settle at the bottom of the casks, and the water may be drawn off. The casks containing the tar should then be filled with hot water, which may be supplied from the boiler of a steam engine, and the whole again agitated as before. This process may be repeated three times, suffering the tar to subside between each; and twelve hours should be allowed for settling from the last water, so that the whole of the tar and water may become separated, the water rising to the top of the cask, and the tar left at bottom, in a pure state.

But, as some of the water will yet remain mechanically combined with the tar, it is proposed that the tar should be subjected to the process of distillation. For this purpose, a still, capable of holding one hundred and twenty gallons, may be employed, in which about fifty gallons at one time may be operated upon, when, by a gentle heat, the water, and other impurities which the tar may have retained, will be driven off. As soon as the water appears to have evaporated, and the spirit runs fine and clear, the process of distillation should be stopped, and, when cold, the pure tar may be drawn off, and set apart for the purpose of being employed as contemplated in the patent.

The tar thus purified may be now converted into black; or it may be subjected to further rectification to divest it of the mineral pitch or asphaltum which is combined with the oil and spirit: the latter is to be preferred; because the mineral pitch, or asphaltum, is only inflam

mable at a high temperature, which renders it more troublesome to use in the process here contemplated, and also would cause the apparatus to require frequent cleaning from the carbonized pitch deposited. In order, therefore, to get rid of the mineral pitch or asphaltum, forty gallons of the tar are to be introduced into a still, as before; and, instead of stopping the operation as soon as the spirit begins to come over, the distillation is continued with a strong heat, so as to force over the whole of the oil and spirit, leaving the residuum of asphaltum in the still this process, however, is known to every chemist, and need not be further explained.

In Plate VI. is exhibited, at fig. 1. a rude representation of the apparatus employed in preparing and collecting the fine light spirit black, produced by the combustion of the oil and spirit of coal-tar after its having been purified as above described. a, is the brickwork which supports a number of burners issuing from a tube, b, within, and here shewn by dots, as passing along its whole length. Fig. 2 is a section of the brickwork, with the tube, burner, and receiver, as will be described hereafter. The tube may be called the tar main, as it is intended to be filled with tar: it is constructed of castiron, and from it issues several (in this figure twentyfour) jets or burners, c, c, c: any other number may be employed. d, is a furnace under the tar main, the flue of which extends along, for the purpose of heating the tar to the boiling point, in order to facilitate the process. From the main, b, the tar flows into the jets, c; wicks are introduced into the jets, and, when set fire to by a red hot stick, will burn and emit a very considerable quantity of smoke; which it is the object of this apparatus to conduct through many passages, for the purpose of collecting its sooty particles.

There are a number of hoods, e, e, e, or bonnets, as

they are termed, all of which, through their pipes, have communication with, or lead into, a main chimney, ƒ, ƒ, Into these hoods or bonnets, the smoke of the burners ascends, and from thence passes into the main chimney, ƒ, and thence through the smoke tubes into the box, g: here the heaviest particles of the black deposit themselves; but, as the smoke passes on through the farther pipes, a deposition of the second, or finer, particles of black takes place in the box, h. From hence the smoke proceeds through other pipes into a series of canvas bags, i, i, i, which are proposed to be about eighteen feet long, and three feet diameter. These bags are connected together at top and bottom alternately, and through the whole series the smoke passes up one bag and down the next, depositing the fine black, called spirit black, upon the sides of the canvas. After the jets have continued burning for several days, the bags are to be beaten with a stick, so that the black may fall to the bottom; and, when a sufficient quantity has accumulated, the bags may be emptied and swept out. Thus, seventy or eighty bags may be employed; so that the smoke should pass through a length of about four hundred yards, the farthest of which will be found to contain the finest black. The last bag should be left open, in order to allow the vapour to escape into the open air.

The main tar tube will require to be emptied every four or five days, in order to clear it from the pitchy matter that may have subsided from the burners, and they also will require to be frequently poked with a wire, to clear off the black which forms upon their edges, and to drive down the carbonized tar which attaches itself to the upper part of the jets.

Inrolled, December, 1821.

77

Original Communications.

On the Reduction of any Volume of Gas at one Temperature, to its Volume at another.

As it is important, in experimental chemistry, particularly where subsequent comparison is required, to obtain every possible accuracy in the reduction of any volume or quantity of gas at one temperature, to its volume or quantity at another, I have constructed a table for this purpose on different principles to those usually met with.

Without entering largely on the subject, I shall proceed to describe the mode by which the table subjoined is calculated, leaving it afterwards to the judgment of others to discover the errors of the customary method, as applied to the same purpose.

If the assertion be true that all gaseous fluids have the property of maintaining a regular rate of expansion when submitted to heat, there is no other mode by which it can be uniform than by the increment of any individual degree being a proportional part of the volume at that degree of heat next preceding, and of no other. It will therefore be a series in geometrical progression; where, calling the volume V, the ratio R, and placing T for one degree of temperature, the following terms are produced: V, VRT, VRT, VRT, VR4T, &c. &c. When only in possession of the first and last terms, and the number of degrees of temperature, and being required to ascertain all the intermediate terms, it is necessary to ᏙᎡᏎᎢ

find the ratio; therefore, &c. = R', the root of which power being extracted, the number sought for is procured.

The method here represented has been the one attended