In order to separate the soap from water, free alcali, and oxide of glyceryl, a large quantity of salt is generally added to the boiling mass, on each addition waiting until it is dissolved; the first addition increases the consistency of the mass, while each successive portion renders it more fluid, till it looses its threading character, and drops from the spatula in short thick lumps. As soon as the congelation is complete, i.e., when gelatinous flocculæ separate from a clear watery liquid, the fire is extinguished, the soap suffered to collect on the surface, and cooled either on the liquid, or ladled out, and suffered to get solid,

In the former case it is impure from water, free alcali, and other impurities of the lye, and is therefore ill adapted for commerce, although sufficiently good for domestic purposes. As in other chemical operations a precipitate is purified by boiling it in a fluid on which it is insoluble, so soap is purified by a solution of salt rendered alcaline.

The soap of the first boiling is either re-dissolved in weak alcaline lye, and precipitated by salt several times, or it is boiled with an alcaline solution of salt several times, by which means it is rendered much purer. When the saponified fluid is made with potassa, the salt (chloride of sodium) operates in a two-fold manner: it dissolves in the pasty liquid, and decomposes with the potassa salts of the fat acids, forming on the one side cloride of potassium, and on the other soda, or soda-soap. That a decomposition takes place is evident from the altered consistency of the fluid mass. Since chloride of potassium has not the property of separating soap soda, a larger quantity of salt is added. When potassa-lye is employed in soapmaking, the first salting requires more than twice the quantity of salt. In the preparation of potash soaps, a concentrated potassa lye is employed for separating the soap. Acetate, or tartrate of potassa, may be employed on a small scale. In the manufacture of soaps, the saponification of the fats is not completed by the first treatment with weak lyes; and the subsequent repetition of fresh lyes, beside purifying, also renders saponification more perfect.

In the saponifying olive and other oils, the mixture often attaches itself to the bottom of the vessel, and is burned; in these cases the alcaline lye is previously mingled with salt, so that the forming soap is obtained in a state of fine division, and yet prevented from forming a perfect solution. For common house use, soap of the first boil is only treated once with salt; that for commercial purposes is suffered to swell up in a weak salt lye, by means of which it takes up fifteen to twenty per cent. water. Grain soap (Kernseife of the Germans) is generally coloured bluish, or greenish, from sulphuret of iron, or copper, or from iron, or copper-soaps. By cooling, these colouring matters collect more or less in certain points, which gives a marbled appearance to the hard soap. Marbling is generally produced by the addition of sulphate of iron, or peroxide of iron, to the still soft mass.

For white soap, it is rendered fluid by heating it in a saline, alca

line lye, and kept in the covered vessel until all the colouring matters have subsided. The more water the soap has taken up in this operation, the more perfect the separation of the impurities, the whiter the soap. Now, since this water is not separated, but sold in the soap, it follows that it has much less real value than the grain soap. The white soap contains from forty-five to seventy, marbled soap from twenty-five to thirty-five per cent. water.

The manufacture of soft soap is the simplest of all. The drying oils, either alone, or mixed with train oil, tallow and other fats, are kept boiling with dilute potassa lye until the saponification is completed, i.e., a mass is formed which draws into long transparent threads. Particular care is had in its preparation to the dilution of the lye, for all soft soaps are insoluble in moderately strong potassa lye, and may be precipitated from their solution by the addition of strong lyes. The fluid would therefore appear cloudy, milky, with an excess of strong lye, and by adding water would become pasty, or gelatinous. A deficiency of alcali produces an acid oleate of potassa, which attaches itself in thick masses to the bottom of the vessel; but an addition of lye changes it into a neutral salt. Oxide of glyceryl is not separated from soap, although it might be done by the final use of strong alcaline lyes.

The soft soaps of commerce have a greenish, or greenish brown colour; they are transparent in thin laminæ, shining, soft but not fatty to the touch, of a peculiar odour, and have an alcaline re-action. Tallow is often added to them, which disseminates crystalline particles of stearate of potassa; communicating to them a peculiar grained character. Chevreul and Thenard found in commercial soft soap 39.2 to 44 per cent. oleic and margaric acids, 8.8 to 95 potassa, and 465 to 52 water. They always contain hydrated oxide of glyceryl and delphinate of potassa, derived from train oil, whence their peculiar odour.

When an alcaline soap is mixed with an earthy, or metallic salt, volumnious white or coloured precipitates ensue, in which the alcali is replaced by the earth, or metallic oxide. Thus the salts of lime, magnesia, &c., throw down lime, magnesia, &c., soaps. Hence the curdling appearance, when soap is used with hard waters, arises from the union of the lime or magnesia they contain with the fat acids. If carbonate of lime be in the water, it may be thrown down by a little caustic potassa or lime, which will render it softer; if sulphate of lime, or a magnesia salt be present, pearlash, (ash-lye) will separate the earths.

Description of a new Universal Photometer. By DR. CHARLES SCHAFHAEUTL, of Munich Assoc. Inst. C. E.*

THE inadequacy of the photometric instruments invented by Pictet, Rumford, and others, is universally acknowledged. The bromide • Trans. of the Inst. of Civ. Eng.

of silver, as used by Sir John Herschel, although extremely sensitive, is only slightly affected by artificial light.

These circumstances induced the author to complete the present instrument, which he contemplated about twelve years since.

The intensity of the undulations of gaseous fluids, as well as that of the air, is proportional to the amplitude of the oscillations, or, more properly, to the square of the amplitude.

A wave of light striking the retina must create a similar vibratory motion in the nerves of the retina, because the velocity of the molecular movement of the nerves depends upon the force with which they have been struck by the original wave, and if this velocity could be measured, it would show at the same time the intensity of light.

It is scarcely possible to obtain a direct accurate measurement of this velocity, but if the time during which the vibratory motion of the nerves ceases be ascertained, the velocity of the vibrating molecules, and, therefore, the intensity of light may be determined; because the duration of an impression on the retina is dependent on the resistance which the molecules of the nerves oppose to every force striking them; but as this resistance of the nerves increases as the square of the velocity, four times the momentum, or intensity, is necessary to double the time of duration; or, in other words, the intensity of the pencil of rays is as the square of the time of the duration of that impression made on the nerves of the retina.

The new photometer consists of a brass bar fixed vertically in a stand, carrying at its upper end a small tube in two parts, which may be lengthened from five to ten inches, if requisite. This eye tube has at each end a sliding plate pierced with holes of corresponding diameters. From the bottom of the bar a projecting arm sustains the lower end of a strip of rolled steel, eighteen inches long,

inch broad, and inch thick; this has at the upper end a thin plate, pierced with a small hole, corresponding with the holes in the sliders, and standing one-eighth of an inch from one of them: upon the main bar is a prism with a slit in it, through which the strip of steel passes; this prism can be moved up and down, by a rack and pinion, so as to lengthen or shorten the vibrations of the strip.

The method of using the instrument, is to adjust the two holes at the opposite ends of the horizontal eye tube, so that they perfectly correspond, and do not permit any rays of light to enter, unless the plate at the extremity of the spring be pushed aside. The light to be compared is then placed at a certain given distance behind the plate, so that by bringing the axis of the hole which is pierced in it into the axis of the tube, a small pencil of light may enter the pupil of the eye. The prism is then placed at 100 of the scale on the side of the brass bar, and the steel strip caused to vibrate gently. A luminous disc immediately appears, accompanied by scintillations, which are caused by the impressions on the retina being interrupted by dark intervals: the prism is then gradually raised, until the

length of the vibrations of the strip being diminished, and the velocity increased, the luminous disc appears perfectly steady and clear. The length of the vibrating portion of the strip is then read off by the verniers marked on the brass rod, and compared with the whole length of the spring, measured from 100, which is considered as unity. The number of the vibrations to be computed from the found length of the spring, are inversely to the numbers of vibrations of the whole length, as the squares of their relative lengths. Hence are constructed the formula for calculation, which are given at length in the communication.

A fresh luminous impression is made on the retina as often as the circular aperture in the screen on the top of the spring cuts the axis of the tube. If the duration of the small vibration of the nerves of the retina is shorter than the time of a vibration of the spring, a dark interval appears between the two luminous impressions. In this case the vibration of the spring is shortened until the next impression returns just as the first ceases, and therefore the dark interval disappears; then by measuring the length of the shortened spring, the number of vibrations can be computed, and from them the intensity of the light.

Crane's Anthracite Iron.*

Decision of the Court of Common Pleas, affirming the validity of the Patent granted to George Crane, Esq., for Smelting Iron with Anthracite Coal. Delivered at Westminster Hall, June 13th, 1842, by Lord Chief Justice Tindall.

THE Lord Chief Justice :-This was an action on the case for the infringement of a patent granted to the plaintiff on the 28th of September, 1836, for an improvement in the manufacture of iron. The declaration was in the usual form, and the defendants pleaded thereto, first, that they were not guilty; secondly, that the plaintiff was not the first and true inventor of the said improvement-upon each of which pleas issue was joined; thirdly, after setting out at length the plaintiff's specification, the defendants pleaded that the alleged improvement therein described was not a new manufacture, invented by the plaintiff within the intent and meaning of the statute, as to the public use and exercise thereof in England-which allegation was traversed by the plaintiff in his replication; fourthly, the defendant pleaded that the nature of the plaintiff's invention, and the manner in which it was to be performed, were not particularly described, or ascertained by the plaintiff, in his specification-upon which plea issue was joined, and in their last plea, the defendants, after referring to the plaintiff's specification before set out in the third plea, stated the grant of letters patent, dated September 11,

From the Cambrian.

1828, to one James Beaumont Neilson, for an improved application of air to produce heat in fires, forges, and furnaces. where bellows and other blowing apparatus were required-that Neilson's invention was the production and application of a hot-air blast, and was in public use with Neilson's license in the smelting and manufacturing of iron from iron stone, and was the hot-air blast in the plaintiff's specification mentioned-that the plaintiff could not use the hot-air blast mentioned in his specification without Neilson's license, and that he had obtained such license before the grant of his letters patent, and that the using by the plaintiff of the hot-air blast, in the smelting of iron from iron stone, combined with anthracite or stone coal, as mentioned in his specification, was a using and and imitating of Neilson's invention, whereby the plaintiff's invention is void. The plaintiff replied to this last plea, that Neilson's invention was not the same hot-air blast, and that the machinery and apparatus adapted for the application thereof, mentioned and referred to in the plaintiff's specification, was not, nor was the using by the plaintiff of the invention, as described in his specification, a using and imitating of Neilson's invention, described in Neilson's specification; which allegation is traversed by the defendants in their rejoinder. At the trial before me, a verdict was entered for the plaintiff on all the issues, subject to the opinion of the Court, upon the evidence given at the trial, as contained in a report agreed upon between the parties-the Court being at liberty to draw the same inference from it as a jury might draw. On the argument, it was contended by the defendants, that the verdict ought to be entered for them on each of the issues joined on the record; but as the main question between the parties turns on the the third issue, which involves the question whether the invention of the plaintiff is a manufacture within the intent and meaning of the statute of Jamesthat is, whether it is or is not the subject matter of a patent-and as the determination of this issue in favour of one party or the other will render the decision of the other issues free from difficulty, the simplest way will be to apply ourselves in the first instauce to that question. Now, in order to determine whether the improvement described in the patent is, or is not a manufacture within the statute, we must in the first place ascertain precisely what is the invention claimed by the plaintiff, and then, by the application of some principles admitted and acknowledged in the application of the law relating to patents, and by the authority of decided cases, determine the question in dispute between the parties. The plaintiff describes the object of his invention to be the application of anthracite or stone coal, combined with hot-air blast, in the smelting or manufacture of iron from iron stone, mine, or ore; and states distinctly and unequivocally at the end of his specification, that he does not claim the use of a hot-air blast, separately, as of his invention, when uncombined with the application of anthracite or stone coal; nor does he claim the application of anthracite or stone coal when uncombined with the using of hot