tion is daily becoming more apparent. The known phenomena of isomerism, allotropy, phosphorescence, and those obscure phenomena named catalytic, are now so numerous, that it is evident mere substantial differences are not by any means the only ones of importance for the consideration of the chemist. Substantial differences or resem blance no longer afford a means of predicating diversity or identity; the means of doing so must be sought elsewhere than in the mere elementary composition of substances, perhaps even elsewhere than in their constitution.

Chief among the subjects which call for the chemist's study are the nature of the cause of chemical action and the phenomena of heat. The co-relation of those modes of energy which give rise to phenomena of chemical change, of heat, electricity, light, and magnetism-at present but somewhat vaguely indicated-presents a fertile field of research to the chemist. The doctrines hitherto current among chemists with regard to these forces, or as they may perhaps be more properly defined, modes of energy, are now effete, or require remodelling to bring them into accordance with the knowledge of the present time. This has become especially necessary as regards the phenomena of heat, in consequence of the intimate connexion that has been shown to exist between these phenomena and those of mechanical force. Whether heat really consists in a vibratory or other motion of the molecules of substances, or not, is probably still a question, but it is one well worthy of being examined. In some form or other, this view of heat has long been entertained. Without going back so far as the time of Aristotle, it will be sufficient to mention the names of Bacon, Locke, Newton, Boerhaave, Boyle, Rumford, and Davy, as supporters of such a view, in order to show that it has claims on the consideration of both chemists and physicists.

Professor Tyndall, adopting in the broadest sense the theory that heat is motion, gives, in the lectures he has just published, an exposition of the physical phenomena of heat in accordance with this theory. Taking as the basis of his argument Mr. Jouie's determination of the "mechanical value of heat," and the demonstration of the mutual convertibility of heat and motion, or mechanical force, he illustrates the applicability of the dynamic theory of heat in the forcible manner which is peculiar to him, by the production of heat by friction, by the phenomena of expansion, specific and latent heat, conduction, and radiation. In all cases heat is supposed to consist in the vibratory motion of the atoms of molecules of bodies, and these are supposed to swing in an ether of extreme tenuity which permeates all space and all substances.

This assumption of the existence of an ether, whatever may be its advantages as a theory, appears to be open to the same objection that was so reasonably urged against the doctrine of phlogiston or against the hypothesis of heat being an imponderable substance. It is not quite easy to see why, if heat be a vibratory motion of molecules, that vibration should not be regarded as taking place without the intervention of this hypothetical ether; or why it should not be admitted that, according to the view put forward by Newton in his "Optics," the particles of bodies act at a distance upon one another in virtue of their attraction.

The opinion that heat consists in motion, or that it results from the percussion of the atoms or molecules of substances, is very clearly put forward by Newton. He refers the heat evolved on mixing sulphuric acid and water to a great motion on the parts of the liquids, which, in mixing, coalesce with violence, and rush towards one another with an accelerated motion, and clash with great force.

Black strongly dissents from Bacon's view, that heat is motion, a rapid tremor or vibration of the particles of solid bodies. He says:-"I cannot form to myself a conception of this internal tremor that has any tendency to explain even the more simple effects of heat, or those phenomena which indicate its presence in a body."

225

In accordance with this objection, it is perhaps worth mentioning that those substances in which vibratory motion is most readily produced, such as steel, are less susceptible of being heated by a blow than such substances as lead, in which the parts are mechanically displaced by percussion. In fluids, also, where the mobility of particles is greater than in solids, the thermal effects of friction or mechanical force are less than in solids, where the particles are apparently less susceptible of being set in motion among themselves. It would seem that these facts point rather to the inference that heat, or at least sensible thermometric heat, is a result of the stoppage of motion rather than motion itself; in fact, a mode of energy rather than a mode of motion.

Professor Tyndall insists strongly upon the necessity of clearness of conceptions in regard to the phenomena of heat and their cause, and there can be no question as to the vast importance of such a character of the ideas formed with regard to this or any other class of physical phenomena. He also maintains that conceptions of the invisible part of physical phenomena must be obtained by means of proper images derived from the visible. But it may be asked,-What are "proper images" of the invisible part of physical phenomena, which are also unknown? If imagination, as Professor Tyndall contends, is to be allowed to furnish those images, our theoretical views will be likely to be better representations of fancy than of fact, and that is a result certainly not to be desired. The use of such comparisons as those between the waves of the sea breaking on the shore and waves of light and heat breaking on the atoms of bodies, or the description of an electric current breaking impetuously upon the molecules of a platinum wire, is liable to produce distorted and erroneous ideas rather than strict conceptions of physical facts; and as these illustrations are applied to an hypothesis, it is doubtful whether the fixity of ideas they are calculated to confer is not a greater disadvantage than their effective nature is an advantage. Goethe has well remarked that the disadvantages of hypotheses do not result necessarily from their truth or falsehood, but from their becoming established as articles of faith which no one ventures to entertain a doubt of; and that this is really the misfortune from which centuries suffer.

In the definition of energy, at p. 137, there appears to be some omission of a due consideration of those effects which, though not consisting in motion, are the results of the same activity or energy that under other circumstances may produce motion. Potential energy is defined as the power of motion which a suspended weight possesses, but which has not yet been exercised by falling. The antithesis of this is actual energy, or the force acquired at the end of the fall. Thus, in the case of a mass of lead suspended above the ground, or resting upon the ground, it is represented to be in both instances "dead and motionless," having "no energy," but that by raising it; there is, then, "an action possible to it, which was not possible when it rested on the earth: it can fall;"

there

The

is "conferred upon it a motion-producing power." accuracy of this representation may be questioned. It is true there is a difference between the mass when resting upon the ground and when raised above the ground, as regards the possibility of its motion; but, as regards energy, is the condition of the mass entirely changed? To hold the mass suspended, a continuous exercise of energy is requisite, proportionate to the magnitude of the mass. Between it and the earth the energy of attraction is exercised equally while it is suspended and when resting on the ground. In the latter case it is manifested as pressure against the support, which presents a continuous and uniform resistance to the motion of the mass, and on which the mass of lead rests without the possibility of falling. In both instances energy is exerted equally, but while it is so opposed there can be no dynamic effect. In falling the same energy of attraction is exerted, and it is

226

then unopposed, and accumulates, producing accelerated motion. The term potential energy can only be applied in reference to motion, and in this sense a body resting on the ground has no potential energy, because it cannot fall. But the raising of the mass of lead above the ground does not confer upon it a motion-producing power; all that it does is to place the mass in a condition admitting of its energy being exercised accumulatively in producing motion, instead of being expended momentarily as pressure. The only difference between the supported mass and the falling mass is in regard to the possibility of motion and the capability of performing work. If the term energy is used with this limitation, as denoting merely a capacity to effect changes, it will not involve any physical inconsistencies, as it would if applied to the result of the mutual activity of masses under all conditions.

"

A Manualof Elementary Chemistry, Theoretical and Practical. By the late GEORGE FOWNES, F.R.S. Ninth edition, revised and corrected. Pp. 820. London: Churchill and Sons, 1863.

In the very numerous alterations and additions effected by the editors of this admirable class-book from time to time, the original design of Professor Fownes has not been obscured. Each successive edition now appearing at intervals of two years, although containing concise reports of chemical progress in the various departments of the science, yet does not show any marked increase in the bulk of the volume. A typical process having been once described with sufficient fulness, the editors content themselves in the case of new discoveries of analogous character with condensed descriptions, which we may aptly designate by borrowing a chemical expression, and calling them "wellcrystallised."

The general ecope and plan of Fownes' " Chemistry" is so thoroughly known and appreciated, that it is quite unnecessary to review these points here. We can only say that this ninth edition is still better than the eighth; that the chief recently ascertained facts of chemistry are duly incorporated in the work; that the essay on the unitary system and notation of Gerhardt appended to the manual has been rendered more complete; and that it is with justice that the editors say in their preface

"Each part has received important additions, and the whole work has throughout been carefully revised.

"In inorganic chemistry an outline of spectrum analysis, and of the great discoveries made by it, and an abstract of the researches of Mr. Graham on diffusion and dialysis, are inserted.

"In organic chemistry, an account of the recent extension of the theory of acids and polyatomic alcohols, and a chapter on the new colouring matters derived from coaltar, form the chief additions. Throughout the whole of this portion of the work the results of the latest researches of importance are recorded.

"In animal chemistry a notice of the remarkable experiments of Pettenkofer on respiration has been added.”

NOTICES OF PATENTS.

Grants of Provisional Protection for Six Months. 641. Henry Revell Spicer, Clement's Lane, Lombard Street, London, "Improvements in protecting and preserving the bottoms and sides of ships and other submerged surfaces from oxidation or fouling by incrustation, the attachment of barnacles, the action of animalculæ, or from any other like causes of injury."-Petition recorded March 6, 1863.

771. Samuel Healey, Elizabeth Street, Hackney Road, London, "Improvements in the manufacture of zinc, and in the apparatus employed therein."

CHEMICAL NEWS, May 9, 1863.

783. John Henry Johnson, Lincoln's Inn Fields, London, "Improvements in the manufacture of zinc, and in the apparatus employed therein."-A communication from Adrien Muller. Paris.

450. John Gray and Joseph Hudson, Botolph Lane, London. "Improvements in the treatment of steatite, and in its application to certain purposes."-Petition recorded February 18, 1863.

667. William Wood, Monkhill, near Pontefract, Yorkshire, "Improvements in the manufacture and ornamentation of Pomfret or liquorice cakes, rolls, sticks, and pipes, and other similar articles of confectionery."-Petition recorded March 11, 1863.

956. Isham Baggs, Cambridge Terrace, London, and William Simpson, Tovill Upper Mills, Kent, "Improvements in purifying and treating coal gas, sulphuretted hydrogen, and other gases containing sulphuretted hydrogen, and in obtaining sulphur, sulphuric, and other acids in such treatment."

551. Henry Fehr, Fenchurch Street, London, "Improvements in the treatment of mineral oils."-Petition recorded February 27, 1863.

663. John Cassell, La Belle Sauvage Yard, London, "Improvements in moderator lamps to adapt them to the burning of petroleum and other mineral oils and hydrocarbons."-A communication from Louis Martin, Paris. 679. James Polkinghorne, Redruth, Cornwall, “Improvements in treating tin ores and in apparatus for treating ores and matters containing arsenic."-Petitions recorded March 12, 1863.

714. William Henry Emett, St. George's Terrace, South Kensington, London," Improvements in processes for facilitating and combining the art of writing with engrav ing together on stone, applicable to maps, plans, specifications, and other lithography, which improvements are also available for re-transfers to zinc or stone, or printing from original."

717. Georges de Laire, Imperial Mint, Paris, "Improvements in the manufacture of brown colouring matters." Partly a communication from Charles Girard, Lyons, France."-Petitions recorded March 17, 1863. 732. Auguste Morel, Rue du Marché, Brussels, "Improvements in apparatus for generating carbonic acid.”

735. Ellis Lever, Manchester, "An improved composition for the coating and preservation of canvas and other materials to make them waterproof and non-inflammable."

752. Fedor de Wylde, Trinity Square, Tower Hill, London, "Improvements in the manufacture of cement from gypsum."-Petitions recorded March 20, 1863.

755. Charles de Groote, Brussels," Improvements in the construction of lamps with circular burners or wicks for the combustion of petroleum, schist, and other volatile oils, parts of said improvements being applicable to gasburners, night lights, and lamps burning spirits and animal oils."

788. Robert Mushet, Coleford, Gloucestershire, “An improvement or improvements in treating steel and iron prepared by the pneumatic process."

Notices to Proceed.

521. William Readman, Glasgow, N.B., "Improvements in the manufacture of carbonate of magnesia, and of iodine and kelp salt, and other products from kelp."-Petition recorded February 25, 1863.

3299 Richard Archibald Brooman, Fleet Street, London," Improvements in treating liquorice root to obtain liquid and solid extracts therefrom."-A communication from Frumence Nicolas Frezon, Paris.

3312. Astley Paston Price, Lincoln's Inn Fields, London, "Improvements in the manufacture or production of blue colours."- A communication from Augustus Eisenlour, Heidelberg, Grand Duchy of Baden.-Petitions recorded December 10, 1862.

3383. Edmond Lepainteur, Paris, "Improvements in the fabrication of a salt for dyeing textile materials.”

CHEMICAL NEWS,}

May 9, 1863.

3353. John McInnes, Liverpool, and Elijah Freeman Prentiss, Birkenhead, Cheshire "Improvements in the distillation and treatment of petroleum and other like oils to obtain products therefrom, and in the apparatus to be used therefor, parts of which can be applied for distilling other liquids."

3355. George Cockburn Warden, Islington, London, "Improvements in ornamenting textile fabrics, leather, and other surfaces, in a cement employed therein, which is also applicable to the waterproofing of fabrics and materials, and in apparatus for applying and spreading such waterproof cement."-A communication from Adolph Baldamus, Berlin, Prussia.

3361. John Louis William Thudichum, Kensington, London, "Improvements in collecting human excreta, and in the apparatus and means employed therein."

3363. Rudolph Schomburg, Onslow Terrace, and Adolph Baldamus, Surrey Terrace, Lorrimore Road, Surrey, "Improvements applicable to all kinds of oil used for illuminating purposes, whereby combustion thereof is rendered more perfect, smoke prevented, and the purity of the light increased."

227

them are likely to be successful in effecting preservation, report :-"There is not one which we at present feel justified in proposing that the Committee should definitely recommend as a preservative, either for general or local application."

They allude to secret processes, regarding which they say they can offer no opinion, but they express a doubt of the applicability of any suggestion which would demand the veil of secrecy for protection. Concurring in this view, it may be further noted that even if such applications were found successful in sample or experiment, no security would be afforded for a corresponding success in any subsequent large operations. They recommend that a series of experiments should be conducted under chemical supervision for a considerable period of time, and the Com mittee are most reluctantly compelled to coincide with them, and to urge upon the Government the adoption of such a course.' I am, &c.

Bathvillite.

B. H. PAUL.

To the Editor of the CHEMICAL NEWS.

"

SIR,-"Ein Untersucher,' a correspondent in the CHEMICAL NEWS of April 18, makes some remarks on a short paper by Mr. Greville Williams which appeared in the NEWS of March 21. These remarks seem to me to be

CORRESPONDENCE.

Preservation of Stone from Decay.

To the Editor of the CHEMICAL NEWS. SIR,-A statement appeared in the Times the other day in reference to this subject, which is not only incorrect, but unfair to some of those who have made experiments with a view to the preservation of the stone of the Houses of Parliament. It is said that "Mr. Szerelmey, a gentleman well known for his most curious chemical discoveries in hardening stone. is, up to the present time, the most successful of all the many competitors for preserving the Houses of Parliament from further decay, by indurating the surface of the stone with a fluid silica, which, it is asserted, renders the stone beneath perfectly indestructible."

It is impossible to say what curiosity may attach to Mr. Szerelmey's method of treating stone with a view to its preservation, since that method is professed to be kept by. him a profound secret.

As to the success which he has achieved in comparison with other competitors, there is no doubt, however. In whatever way his connection with the Houses of Parliament may have been a success to him, it is certain that there has been no successful result in the preservation of the stone from decay. There is every reason to believe his method of treatment to be as worthless as those tried by others, and in confirmation of this opinion the report of the committee appointed to inquire into the subject speaks unmistakably:

"With regard to the processes which have actually been applied, whether experimentally or extensively, your Committee are decidedly of opinion that the discovery of a proper mode of treating stones in a state of decay has not yet been made, and there is no evidence whatever on the building itself to induce them to believe that the decay, where decay has arisen, has been arrested, or that permanently the decay has been prevented by any of the processes yet applied."

The chemical sub-committee appointed to inquire into the proposed method of treatment as to whether any of

on any scientific topic. I am an occasional reader of your excellent journal, and, on the whole, am inclined to take the opposite view to Mr. Williams when he says that the Torbanehill mineral is not a coal; at the same time, I can see no harm in that substance being designated "Torbanite," even though it be a coal. Mr. Williams is as much entitled to call it "Torbanite" as any one else to call "blind coal"" anthracite." In this way the name may be used to designate a variety of coal: it does not necessarily imply that the substance is not coal.

A similar remark applies to the objection of "Untersucher" to the word "Photogene." He must admit that the term "Photogene," when applied to an oil used for the light it gives, is a more elegant and terse appellation than Paraffin oil.

Surely "Untersucher" cannot believe that Mr. Williams would not know a coprolite when he sees one. A mere reader of Mr. Williams' paper, like myself, can see in the analytical details given abundance of reasons for rejecting the statement of "Untersucher," that the mineral analysed was a coprolite.

Again, what is the meaning of the closing remark of "Untersucher's" letter when he says, does Mr. Williams think that no chemist ever imagined such an apparatus as that Mr. Williams figures in his paper. Doubtless many chemists may imagine such things, but it remains for the busy workers amongst them to make and to use them.

Will any one say that it was out of place for the author of the best "Handbook of Chemical Manipulation" to describe the means whereby he so successfully analysed a mineral, operating on such a small quantity as three decigrammes (about five English grains)? Mr. Williams' object in describing the apparatus was evidently to bring this prominently forward. I am, &c.

Dumfries.

BOGHEAD COAL WITHOUT Choler.

MISCELLANEOUS.

Adulteration of Linseed.—At the adjourned meeting of the linseed trade on the question of the prevention of adulteration, and the proposal to sell by weight instead of measure, held at the Baltic Coffee-house on Tuesday morning, the following report was unanimously received

228

and adopted, and a permanent committee was nominated to manage the proposed association:

"The committee, after seeking for information from the most practical sources, have come to the conclusion that the Marseilles system can easily be brought into use in this country. Along with this system they also recommend should be adopted the practice of selling linseed by weight, that is, by the ton of 20 cwt., or 2,240lb., whether sold on delivered, or cost, freight, and insurance terms.

"A strong opinion having been expressed in committee by the members from Hull that it was necessary to get the large interest connected with the seed trade at that place and in its vicinity to confirm the views entertained by the committee, a public meeting was called there, at which a deputation from London attended.

"At that meeting, after a full discussion of the whole subject, it was resolved

That it is the opinion of this meeting that the Marseilles system should be adopted in this country for all qualities of linseed imported from any port whatever, with the amendment proposed by Dr. Longstaff, that when linseed contains a less admixture than is equal to 4 per cent. of non-oleaginous seed, the difference should be added to the selling price.'

"At the meeting of your committee, after the return of the deputation fron Hull, the following resolutions were passed:

"1. That with a view to carry out the original recommendation of the trade, as expressed at the meeting of the 17th of December last, and further confirmed at the public meeting held at Hull on the 17th inst, this committee unanimously recommend that the Marseilles system, modified, as suggested at Hull, should be adopted in all sales of linseed.

2. That an association, to be styled the Linseed Association,' be formed to promote the importation of linseed as pure as possible, and for the purpose of properly sampling and analysing the seed on arrival.

3. That a committee of management be nominated at the next meeting of the trade, who shall be empowered to frame rules for carrying out the above recommendations.'

"The committee consider that, if seed is in future to be sold by weight, the standard of 2,240lb., or per ton of 20 cwt., will be found most convenient. Oil and cake are both sold in this way.

Mediterranean and Black Sea grain and seed freights are now so calculated, and it is probable, before long, the duties on grain and seed will be levied on the ton of 20 cwt.

"Your committee have only further to suggest that this meeting do at once form an association, and proceed to elect the gentlemen to form the committee of management, who they trust will be able to bring the new system into operation, at latest, by the 1st of January next.

"J. C. D. BEVAN. Chairman.
"J. M. EASTTY, Hon. Sec."

The Oil Springs of America and Canada.— (Review for April) -The uncertainty of commercial prescience was never more completely affirmed than it has been in petroleum during the month that is now past. Practical traders made a solicitous point of clearing out all their stock, ready to buy in at a summer's reduction; and with sapient avidity, contracted at very low rates with their less experienced brethren! Speculators drawing their conclusions from, and adopting the same policy, made very free sales at prices almost incompatible with the cost of production; the penalty of which, as will be seen, even now, lies heavily upon them. Others, not prepared to see an advance such as has been attained, stocked themselves, however, with propriety, ready to invest in more at a discount, and be guided by progressing events The knowledge that what was shipping on the other side is totally insufficient for our European wants-that the present worth of petroleum is utterly inadequate to its merits and universal application

CHEMICAL NEWS, May 9, 1863.

that temporary troubles with the Federals would double, treble, or quadruple prices—that a strong export demand had set in here, and that the longest day was only six weeks off-all these circumstances combined, suggested a general investment, every one feeling that the loss could only be little to the minus, while the gain might be much to the plus. The result shows that this logic was cogent, and it seems probable that for the remainder of this year the petroleum trade will be profitable and gigantic. In the first three months, the American export was equal to the whole twelve months of 1862, and assuming, as we have a right to do, that it will continue at the same, or at an increased ratio, the importations into Europe will approach the value of 4,000,000l. sterling for this year; an augmentation and a position strongly endorsing the prediction that was given, viz., "that the petroleum trade in its day would be second only to cotton." The importations into Liverpool this year are over 70,000 casks and cases, against 3000 casks same time last, yielding in dock and town dues alone nearly 2,000l. for the four months.-From Alex. S. Macrae's Circular, May, 1863.

SCIENTIFIC SOCIETIES.

MEETINGS FOR THE ENSUING WEEK.
May 11. Monday.

GEOGRAPHICAL-15, Whitehall Place. 8.30 p.m.
12. Tuesday.
MEDICAL AND CHIRURGICAL-53, Berners Street. 8.30 p.m.
CIVIL ENGINEERS-25, Great George Street, Westminster.
8 p.m.
ZOOLOGICAL-11, Hanover Square. 9 p.m.
SYRO-EGYPTIAN-22, Hart Street, Bloomsbury. 7.30 p.m.
ROYAL INSTITUTION-Albemarle Street. 3 p.m. Professor
Tyndall, "On Sound."

13. Wednesday.

"

SOCIETY OF ARTS-John Street, Adelphi. 8 p.m. Dr. J. L. W. Thudichum, “ On the Collection and Utilisation of Excrementitious Matter;" and the Rev. H. Moule, "On a System of Earth Sewage.' GRAPHIC-Flaxman Hall, University College. 8 p.m. MICROSCOPICAL-King's College, Strand. 8 p.m. LITERARY FUND-4, Adelphi Terrace. 3 p.m. ARCHEOLOGICAL ASSOCIATION-32, Sackville Street. p.m. Anniversary.

14. Thursday. ANTIQUARIES-Somerset House. 8.30 p.m. ROYAL INSTITUTION-Albemarle Street. Ansted, "On Geology."

3 p.m. Prof.

15. Friday. PHILOLOGICAL-Somerset House. 8 p.m. ROYAL INSTITUTION-Albemarle Street. Odling, "On the Molecule of Water." 16. Saturday. ROYAL INSTITUTION-Albemarle Street. 3, p.m. Prof. Max Müller, "On the Science of Language."

ANSWERS TO CORRESPONDENTS.

All Editorial Communications are to be addressed to the EDITOR, and Advertisements and Business Communications to the PUBLISHER, at the Office, I, Wine Office Court, Fleet Street, London, E.C.

W. A. Dixon. For the present we are unable to entertain our correspondent's proposition. We are, however, obliged for the offer.

SCIENTIFIC AND ANALYTICAL CHEMISTRY.

Disassociation of Water, by M. S. C. DEVILLE. WHEN a current of hydrogen is passed through a porous earthen tube, even rapidly, the gas which issues from the tube is found to be not hydrogen, but atmospheric air. The hydrogen during its passage is diffused through the porous tube, and atmospheric air passes through into the interior by means of endosmose, notwithstanding the pressure caused by the dipping of the discharge tube for several centimetres into water or mercury.

When this porous tube is enveloped in an atmosphere of carbonic acid, by enclosing it in a shorter tube of glazed porcelain, the ends of which are closed by corks perforated to admit the porous tube through them, and also fitted with tubes for passing a current of gas through the annular space thus formed, and a regulated current of hydrogen is passed through the porous tube, while a rapid current of carbonic acid is passed through the outer tube, hydrogen makes its appearance at the discharge from the outer tube, while carbonic acid, almost pure, escapes from the interior tube.

Thus, by means of endosmose, the two gases have changed places, each of them traversing in opposite directions the porous wall of the interior tube. This fact is quite in accordance with the phenomena observed by

Mr. Graham and M. Iamin.

When these tubes, thus arranged, are heated to a temperature of from 1100° to 1300° C., and a current of water vapour is passed through the interior one, while the current of carbonic acid is kept up in the outer tube, the gas collected consists of hydrogen and oxygen mixed

with carbonic acid.

A part of the water vapour undergoes decomposition in the porous tube. The hydrogen, attracted by the carbonic acid in the outer tube, is separated, as if by a filter, from the oxygen; traversing the permeable wall of the tube, while carbonic acid is attracted in the opposite direction, as in the previous experiment, and mixes with the oxygen.

About one cubic centimetre of an explosive mixture of hydrogen and oxygen was obtained from each gramme

of water used.

These phenomena, however, are not quite so simple as above described.

In the first place, whenever hydrogen is in contact with carbonic acid, water and carbonic oxide are formed. Secondly, notwithstanding all precautions in closing the apparatus hermetically, it is impossible to prevent the loss of some hydrogen; consequently, the oxygen is always in excess. Lastly, it is impossible to prevent the presence of a small quantity of atmospheric air being introduced in a state of mixture with the water and

*Comptes-Rendus, lvi., 195.

carbonic acid. The composition of the gas collected was, in 100 parts:

1.

2.

Oxygen. Hydrogen. Carbonic oxide. Nitrogen. 55'7 48.6

24°3 13.1

O 25'3

20

13

The separation of the hydrogen and oxygen may perhaps be effected mechanically as well as by endosmose. This M. Deville is at present endeavouring to ascertain. He has ascertained that water vapour heated in a platinum tube to a temperature near the melting point of that metal is not decomposed to any extent, or at least is reproduced in escaping from the tube.

According to the experiments of MM. Deville and Debray, the temperature of combustion of hydrogen in oxygen does not reach to 2500° C. At this temperature the gases occupy a volume nearly tenfold that which they occupy at o° C. This is the limit of temperature above which water is entirely decomposed. That decomposition is accompanied by a considerable absorption of heat requisite for maintaining the molecules of hydrogen and oxygen at a distance greater than the range of their affinity.

Thus the decomposition of a substance is in all respects analogous to the ebullition of liquids, where the principal characteristic is the invariability of the temperature in the influence of a source of heat of any intensity, provided the pressure remains the same. Vapour of water expands it to tenfold its volume at o° C. It is then is unable to resist the influence of a temperature that decomposed, while its constituents absorb heat, which M. Deville calls the latent heat of decomposition.

M. Clausius has shown that the specific heat of gases and vapours does not vary with the temperature, and this law has been verified by M. Regnault for air between 30° and 225° C. The quantity of heat generated by the combination of one gramme of hydrogen with eight grammes of oxygen is 34,500 units, according to Dulong, Favre, and Silbermann; consequently, 3833 units are generated by the formation of one gramme of water. The quantity of heat absorbed by one gramme of water heated from o° to 2500° C. is expressed by the formula 637+ (2500-100)0.475-1680,

in which 637 represents the quantity of heat requisite 100° C., and the term (2500-100) 0'475 represents the to convert a gramme of water at o° C. into vapour at heat required to raise the temperature of the vapour from 100° to 2500° C. The difference between 3833 and 1680 is 2153, which represents, in heat units, the quantity of heat absorbed by the elements of the vapour at the moment of separation-the latent heat of decomposition.

The relation between the effects of affinity and cohesion in the case of solids and liquids holds good also in the reverse phenomena of volatilisation and decomposition. Admitting this resemblance, it will be seen that the phenomenon of decomposition at a relatively low temperature, or disassociation, corresponds to the vaporisation of a liquid at a temperature below that of ebullition,