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cold water to the outside of the condenser, was soon found in convenient from the great size and expense attendant on the use of this apparatus; and Mr. Watt introduced an internal jet of cold water, which, striking against the steam, instantaneously reduced it to its original bulk, and thus formed a vacuum. draw off the condensing water, as well as to get rid of the air that was extricated during condensation, he found it necessary to employ a small pump, worked by the engine, the size of which was proportioned to the amount of air and water generated in the condenser. In one of the early engines upon this construction, erected at Bedworth, three air-pumps were used; two below, worked by chains connected with the beam, and a third, placed above, which received the hot water raised by the others. In the engines now constructed, only one air-pump is employed, and this fully answers the intended purpose.

"Another improvement introduced by Mr. Watt, consisted in surrounding the upper part of the cylinder with a cap, through a hole in the centre of which the piston rod worked air-tight. The force of steam was then substituted for that of the atmosphere, and at a pressure of more than fifteen pounds on the square inch; so that when a vacuum was formed beneath the piston, steam of considerable impellent force was entering the upper end of the cylinder, by means of a pipe connected with a boiler.

"By thus substituting the force of highly elastic vapour, for the ordinary pressure of the atmosphere, the upper and under side of the piston were preserved at the same temperature, and the supply of steam being regulated by the width of the aperture, any given amount of force might readily be produced. In the atmospheric engine this could not be effected, as the whole pressure of the atmosphere was made to act on the piston, the instant the vacuum was formed by the condensation of the vapour beneath; so that in the event of a pump-rod breaking, by which the elevation of the water might be impeded, and the labour of the engine taken off, the rapid descent of the piston would evidently cause the destruction of the entire apparatus. "Soon after the completion of his first model, Mr. Watt erected an engine for his friend Dr. Roebuck of Kinneil, near Borrowstownness, with whom he was afterwards associated in the manufacture of his improved engine: the latter gentleman, however, in 1774, disposed of his share of the business to Mr. Boulton, of Soho."

Want of room prevents our making any additional extracts from Mr. P.'s work, or attempting an enumeration of the various engines he describes, which could only be satisfactorily accomplished by reference to the numerous plates employed for their illustration.-But it may be adviseable before we finally dismiss the subject, to briefly notice another work of a more general nature, but with much higher pretensions, announced as far

back as 1816, though but just published. We allude to the new edition of Professor Robison's Mechanical Philosophy, edited by Dr. Brewster. The article Steam Engine, after having been revised by the late Mr. Watt and the learned editor, has been put forth by Mr. Murray, as "the only account of the steam engine that can be relied upon." What claims it possesses to this title, may easily be seen by reference to a very simple fact. The last steam engine described in Professor Robison's Mechanical Philosophy, was erected for the Albion Mills, in 1788, since which period we find, by turning to Mr. Partington's appendix, that more than one hundred patents have been enrolled, many of which are of the utmost importance.

Transactions of the Cambridge Philosophical Society, Vol. I. Part II. 1822.

From an accidental cause, we omitted to notice the first part of this Society's Transactions; we, therefore, take an early opportunity of giving a brief sketch of the contents of the present part.

I. Analysis of a Native Phosphate of Copper from the Rhine. By F. Lunn, Esq.

As this paper has been given entire in the Annals, it is unnecessary to notice it upon the present occasion.

II. Upon the regular Crystallization of Water, and upon the Form of its primary Crystals. By Dr. E. D. Clarke.

This communication of the late and lamented Professor is accompanied by a plate, which is indeed requisite to the perfect understanding of his views.

After mentioning various authors who have treated on the same subject, and described the appearances which crystallized water assumes, Dr. Clarke concludes his memoir with observ-: ing: "It is presumed, therefore, that the question respecting the crystallization of water may be set at rest by these phenomena; because it is now no longer a mere inference deducible from observing the intersection and disposition of the spiculæ exhibited by water when frozen upon the surfaces of other bodies, and in its approach to crystallization; but it is a decided fact, shown by regular crystals of ice, that the compound we call water, or hydrogen oxide, crystallizes both in hexahedral prisms. and in rhombi, having angles of 120° and 60°; and that the latter is its primary form. The manner too in which these forms have been displayed may guide to the crystalline forms of other bodies, by inducing a careful examination of the surfaces, points, and interstices of all minerals when they are found as stalactites. The stalactite formation is of all others the most likely forination to bear marks of a regular crystallization; because it is the result

of a process in which the particles of bodies are not carried by a too sudden transition from the fluid to the solid state; but gradually approach, and become united by virtue of their mutual attractions, as the molecule of the fluid which had separated them go off by evaporation or by other causes. And in further confir mation of this, it may be urged, that when the crystallization of the stalactite carbonate of lime, and of other stalactites, especially chalcedony, had been considered as impossible formations, contradictory to the laws by which Nature acts in the stalactite process, yet the primary form of the carbonate of lime is nevertheless exhibited by the stalactites of the cavern of Antiparos, and the primary form of the hydrates of silica by the stalactites of blue chalcedony brought from the Hungarian mines."

III. On the Application of Hydrogen Gas to produce a moving Power in Machinery; with a Description of an Engine which is moved by the Pressure of the Atmosphere upon a Vacuum caused by Explosions of Hydrogen Gas and Atmospheric Air. By the Rev. W. Cecil, MA. Fellow of Magdalen College, and of the Cambridge Philosophical Society.

The author of this paper observes that "two of the principal moving forces employed in the arts are water and steam. Water has the singular advantage that it can be made to act at any moment of time without preparation; but can only be used where it is naturally abundant. A steam-engine, on the contrary, may be constructed at greater or less expense, in almost any place but the convenience of it is much diminished by the tedious and laborious preparation which is necessary to bring it into action! A small steam-engine, not exceeding the power of one man, cannot be brought into action in less than half an hour; and a four horse steam engine cannot be used under two hours' prepara tion."

The engine in which hydrogen gas is employed to produce moving forces was intended to unite the two principal advan tages of water and steam so as to be capable of acting in any place without the delay and labour of preparation.

The general principle of this engine, as described by Mr Cecil, is founded upon the property which hydrogen gas mixed with atmospheric air possesses, of exploding upon ignition, so as to produce a large imperfect vacuum. If two and a half measures of atmospheric air be mixed with one measure of hydrogen, and a flame be applied, the mixed gas will expand into a space rather greater than three times its original bulk. The products of the explosion are a globule of water, formed by the union of the hydrogen with the oxygen of the atmospheric air, and a quantity of azote, which in its natural state (or density 1) constituted 556 of the bulk of the mixed gas; the same quantity of azote is now expanded into a space somewhat greater than three times the original bulk of the mixed gas; that is, into about six times the space which it before occupied;

its density is, therefore, about one-sixth, that of the atmosphere being unity.

According to Mr. Cecil, if the external air be prevented by a proper apparatus from returning into this imperfect vacuum, the pressure of the atmosphere may be employed as a moving force, nearly in the same manner as in the common steam engine; the difference consisting chiefly in the manner of forming the

vacuum.

Mr. Cecil then enters into an estimate of the power resulting from such a vacuum by comparing the effects of equal bulks of steam and hydrogen; this it will be impossible to comprehend without the diagram by which it is illustrated; but the author concludes, that "it appears by calculation that any quantity of pure hydrogen gas will produce more than five times the effect of the same bulk of steam; and in practice the disproportion of their effects is still greater. It is here supposed, that steam produces by condensation a perfect vacuum equal to its own bulk; but this is far from being the case: much of the power is lost by needless condensation by the escape of steam through the piston, besides a considerable deduction for working an air pump, and two water pumps, which are necessary to a steam

engine.

This paper is accompanied with a drawing and explanation of a model of a gas engine. The drawings are adapted to the Isometrical Perspective of Prof. Farish. There is also a drawing of one of a different construction which Mr. Cecil has intro duced on account of its simplicity.

The paper concludes with some observations upon the use of the explosive force of gunpowder as a moving force, and with showing that it cannot be practically useful, for several reasons, and particularly from the corrosion of metals by the sulphur contained in the gunpowder, and by the sulphuric acid which is produced during combustion.

IV. On a remarkable Peculiarity in the Law of the extraordi nary Refraction of differently-coloured Rays exhibited by certain Varieties of Apophyllite. By J. F. W. Herschel, Esq. FRS. of London, Edinburgh, and Gottingen, &c. &c.

In this paper Mr. Herschel refers to the figures contained in the first part of the Transactions; and as without these, it would be imperfectly intelligible, we shall not attempt any analysis of this paper.

(To be continued.)

ARTICLE XIV.

Proceedings of Philosophical Societies.

ROYAL SOCIETY.

June 6. On the Binomial Theorem, by John Walsh, Esq. A paper, by Dr. Davy, was likewise read, entitled "Some Observations on Corrosive Sublimate." It is known that the liquor hydrargyri oxymuriatis of the London Pharmacopoeia, on exposure to light, slowly undergoes decomposition; and it has been asserted that light has a similar effect on corrosive sublimate itself. Dr. Davy relates a number of experiments made to investigate these points. He finds that corrosive sublimate remains unaltered on exposure to light; that it remains unaltered when exposed in solution in media, having a strong affinity for it, as alcohol, ether, muriatic acid, &c. and that decomposition takes place only under circumstances of complicated affinities, as in the instance of the liquor hydrargyri oxymuriatis, and in the aqueous solution, when calomel and muriatic acid appear to be formed, and oxygen evolved.

For the purpose of further illustration of the subject, Dr. Davy describes a series of experiments on corrosive sublimate with alcohol, ether, several oils, muriatic, and the mineral acids, many of the muriates, &c. the results of which hardly admit of being given in the form of abstract. In every instance that an oil, whether volatile or fixed, was heated with corrosive sublimate, mutual decomposition took place, charcoal was evolved, and muriatic acid and calomel formed. Besides, when oil of turpentine was used, some traces of artificial camphor appeared; and when the oils of cloves and peppermint, a purple compound distilled over, consisting of the oil employed, and muriatic acid. With muriatic acid, common salt, and some other muriates, corrosive sublimate formed definite compounds remarkable for their solubility.

June 13.-On the State of Water and Aeriform Matter in the Cavities of certain Crystals, by Sir Humphry Davy, Bart. PRS. June 20.-Some Experiments on the Changes which take Place in the fixed Principles of the Egg during Incubation," by W. Prout, MD. FRS.

The author, after a few preliminary remarks, proceeded to relate his experiments on the recent egg. The specific gravity of new laid eggs was found to vary from 1080 to 1090. Eggs, however, as is well known, on being kept for some time, become specifically lighter than water, owing to the substitution of air for a portion of their water which escapes. Thus it was stated that an egg exposed for two years to ordinary circumstances,