CHEMICAL, NEWS,} Investigations on the Specific Heat of Solid and Liquid Bodies. June 18, 1864. rings thus formed roll rapidly round their curved axes, and go on expanding nearly to the bottom of the vessel before they disappear. Two ionic-like volutes are seen on either side of the rings; these are produced by the perspective of a number of rings seen through, or nearly through, each other, while at the front and back the edges of single rings only are seen. The formation of these rings is thus explained : Air Ring. "In the case of a liquid ring the forces are (1) diffusion, which forms the ring; (2) gravity, which causes it to sink. The resistance is friction retarding (1) the descent of the ring, (2) its diffusion. In the case of a ring of smoke, the forces are precisely the same, only gravity causes it to ascend, and friction retards the ascent. I have attempted to combine both cases in the figure, where the globule a may be either a bubble of PH, about to burst and project a ring of smoke into the air, or it may be a drop of liquid about to descend in water, benzole, ether, &c. The ring of smoke, or the liquid ring, acts as if rolling up or down the inside of a hollow cone, and the Liquid Ring. direction of rotation of the 293 was admirably clear, and kept its form and size unchanged until it became invisible from condensation. We have had frequent rifle practice, but I have not seen a ring made yet from the smoke of the gunpowder." Investigations on the Specific Heat of Solid and Liquid diffusion, and the rate at The author then gives his determinations of a very great number of solid bodies whose specific heat had not Been previously determined; they extend to all the more important classes of inorganic compounds, and to a great number of organic compounds. In the fourth part the author gives for solid bodies of known composition the atomic formula, the atomic weight, the more trustworthy determinations of specific heat, and, corresponding to these, the atomic heats, or products of the specific heats and the atomic weights. The relations between the atomic heat and the atomic rounding medium by its outer surface, which would be equivalent to its rolling up the inner surface of a hollow cone. In the figure, the straight vertical arrows show the motion of the ring up or down, the oblique arrows give the direction of the resultant of the forces acting on the ring, and the direction of the resistance of the medium to this resultant, while the curved arrows show the direction in which rotation must occur according as the general direction of the movement of the rings is upwards or downwards." Aerial rings on a grand scale may sometimes be seen from a factory chimney, the funnel of a steamboat, or the chimney of a locomotive. A friend writing to Mr. Tomlinson says:— "As I was watching a goods train on the line last evening making its way with difficulty up an incline, the engine suddenly shot out from the funnel a beautiful ring of rippled smoke and steam, which separated itself from the general cloud of steam coming from the funnel and rose in the air unbroken and distinct. It was visible until it had gained a height of fifty feet or more. I was too far off to see its rotation; the ring, however, various modifications: 1. When the substance is heated to a temperature at which it begins to soften, and thus to absorb part of its latent heat of fusion. 2. If the substance is heated to a temperature at which it begins to pass into another modification; and Abstract of a paper read before the Royal Society, May 12, 1864. 294 Investigations on the Specific Heat of Solid and Liquid Bodies. {CHEMICAL NEWS, this change, with its accompanying development of heat, is continued in the calorimeter. 3. If the substance investigated is porous, and (as was the case in the earlier methods) is directly immersed in the liquid of the calorimeter, in which case the development of heat which accompanies the moistening of porous substances comes into play. The author arrives at the following results:-From what is at present known with certainty, one and the same body may exhibit small differences with certain physical conditions (temperature, or different degrees of density or porosity); but these differences are never so great as to furnish an explanation of cases in which a body markedly deviates from a regularity which might perhaps have been expected for it, always assuming that the determination of the specific heat, according to which the body in question forms an exception to the regularity, is trustworthy and free from foreign elements. The author then discusses the applicability of Dulong and Petit's law. The atomic heats of many elements† are, in accordance with this law, approximately equal; they vary between 6 and 6-8, the average being about 64. The explanations attempted why this law only approximately holds good, he considers inadequate. In any case there are individual elements which do not obey this law. The atomic heat of phosphorus, for instance, as deduced from direct determinations of its specific heat in the solid state, is considerably smaller (about 54), and still more so are those of silicium (about 4), of boron (about 2·7), and of carbon (18 for diamond). A regularity, to which attention has been already drawn, is, that the quotient obtained by dividing the atomic heat of a compound by the number of elementary atoms in one molecule, is approximately equal to 6:4; equal, that is, to the atomic heat of an element according to Dulong and Petit's law. Thus the atomic heat of the chlorides RCI and RCI has been found to be 12.8 on the average, and of the chlorides RCI2 128 18.5. Now = 43°4 18.5 3 = 55°2 = 2 6.4, and 6.2. The same regularity is met with in metallic bromides, iodides, and arsenides; and according to the author's determinations, it is even found in the case of compounds which contain as many as seven, and even of nine elementary atoms. The atomic heat of ZnKCl, is 43'4, and that of PtKCl, is 552; now 6'2, and 6.1. But the author shows at the same time that this regularity is far from being general. For the oxides of the metals the quotient is less than six; and is smaller the greater the number of atoms of oxygen in the oxide. (From the average determinations of the atomic heats it is, for the metallic oxides Rei 7 27.2 = II'I 9 = 5'6; for the oxides R2, and R23 54; for the oxides RO2 =46.) The quotient is still smaller for compounds which contain boron 5 as well as oxygen (for instance, it is 16.8 42 for the borates, RBO,; it is- 33 for boracic acid, B.03), 16.6 24). It may be stated in a few words in what most of the elements, and in what cases it is less. It is cases this quotient approximates to the atomic heat of near 64 in the case of those compounds which only contain elements whose atomic heats, in accordance with Dulong and Petit's law, are themselves approximately 64. It is less in those compounds containing elements which, as exceptions to Dulong and Petit's law, have a considerably smaller atomic heat than 6·4; and which are found to be exceptions, either directly, by determinations of their specific heat in the solid state, or indirectly, by the method to be subsequently described. Neumann showed that a similar regularity existed in the After Dulong and Petit had propounded their law, case of compounds, that is, that the atomic heats of analogous compounds are approximately equal. Regnault, as is known, has confirmed Dulong and Petit's, as well as Neumann's law, to a considerably greater extent, and for a larger number of compounds, than had been previously done. And Regnault's researches have more especially shown that the elementary atoms, now regarded as monequivalent, are, as regards the atomic heat of their compounds, comparable with the elementary atoms which are to be considered as polyequivalent. Thus, as regards atomic heat, arsenious acid, As, and sesquioxide of iron, Fe,,, or chloride of silver and subchloride of copper, CuCl, may be classed together. Of the applicability of Neumann's law, as hitherto investigated and found in the case of chemically analogous compounds, the author's experimental determinations have furnished a number of new examples. But more interest is presented by his results in reference to the applicability of this law to compounds, to which it had not hitherto been supposed to apply. In comparing compounds as regards their atomic heat, their chemical character has been taken into account, as represented by the formulæ hitherto adopted. Sulphates and chromates, for instance, were looked upon as comparable, but they would not have been classed with perchlorates, or with permanganates. According to more recent assumptions for the atomic weights of the elements, the following salts have analogous formulæ, and the adjoined atomic heats have been determined :— But not even a common chemical behaviour, such as the bodies in this group possess, that is a common haloid character, is necessary in order that compounds of analogous atomic composition shall show the same atomic heat. No one would think of considering magnetic oxide of iron as analogous to chromate of potass, and yet both have the same atomic structure, and determinations of their specific heat have given approximately the same atomic heat for both. Magnetic oxide of iron Fe, CHEMICAL, NEWS, Permanent Stratification Produced by the Spark of Induction. 1864. heat as sesquioxide of iron, Fe,, or arsenious acid, As; with very different characters these compounds have approximately equal atomic heat. But comparability of chemical compounds, as regards the atomic heat, is not limited to the cases in which, as far as can be judged, the individual atoms have analogous construction. We do not regard the atom of binoxide of tin or of titanic acid as analogous in construction to the atom of tungstate of lime or of chromate of lead; nor to nitrate of baryta, or metaphosphate of lime. But if the formulæ of these binoxides are doubled or tripled, they may be compared with those salts, and their atomic heats are then approximately equal, as is the case for compounds of analogous chemical character. The atomic heats are for Binoxide of tin Chromate of lead Permanganate of potass. 2SnO2 = 27.6 273 27'9 290 Pber 28.3 KC19 Perchlorate of potass Binoxide of tin Titanic acid. . Nitrate of baryta. 26.3 414 Ti, 410 BaN 3819 CaP 394 2 6 6 These results seem to give to Neumann's law a validity far beyond the limits to which it had hitherto been considered to apply. But, on the other hand, the author's comparisons go to show that neither Neumann's nor Dulong and Petit's law is universally valid. Neumann's law is only approximate, as is well known. For such analogous compounds, as from what we know at present, are quite comparable, and in accordance with this law ought to have equal atomic heats. Regnault found the atomic heats differing from each other by onetenth to one-ninth. In a few such cases there are even greater differences in the atomic heats, for which an adequate explanation is still wanting. But there are other differences in the atomic heats of some compounds which might have been expected to have equality of atomic heat in accordance with Neumann's law, differences which occur with regularity, and for which an explanation is possible. Certain elements impress upon all their compounds the common character, that their atomic heats are smaller than those of analogous compounds of other elements. This is the case, for instance, with the compounds of boron; the atomic heat of boracic acid is much less than that of the metallic oxides, R., and R.,; the atomic heat of the borates, RBO2, is much less than that of the oxides, R2 = (2RO), and the atomic heat of borate of lead, PbB., is far less than that of magnetic oxide of iron, Fe. The same is the case with compounds of carbon, if the alkaline carbonates R, are compared with the metallic oxides, R = (3RD), or the carbonates, REO, with the metallic oxides, R., and R. It is seen that the compounds of those elements which, in the free state, have selves a smaller atomic heat than most other elements, are characterised by a smaller atomic heat. (To be continued.) 295 fact only, that the alternately light and dark bands are formed in a ponderable matter. I have succeeded in producing, on a semi-conducting surface, an analogous stratification; transverse rays whose durable impression no doubt will facilitate the study of this phenomenon. To prepare this semi-conducting layer, pour on a glass plate some iodised collodion, and then let it undergo all the operations necessary to produce a photographic plate. A suitable surface cannot invariably be obtained. The layer, in fact, does not conduct the electricity when the reduction of the silver is not sufficiently advanced, and the spark passes over without attacking. This is generally the case with solarised surfaces with a reddish tint. If, on the contrary, the silver is completely reduced, and presents a metallic and mirror-like layer, it conducts too well, and the spark traverses without modifying it. Between these two extremes surfaces are obtainable more or less conducting, on which the spark produces more or less compact strata, of very varied appearance. They are not regular, like the bands of light formed in a perfectly homogeneous medium, but, whatever their form, they always appear transversely to the spark; in all my experiments I have not found a single exception. surface, are transparent, which allows of their reproducThese designs, traced by electricity on an opaque Manifold details are lost in this operation which the tion directly on a paper prepared with chloride of silver. microscope reveals on the negative plate. In practising photography, so many negative plates are rendered useless that the simplest way is to use them for the trials, instead of preparing others expressly; and it is very uncommon to be unable to find a suitable surface, especially among negative plates on which the image has been developed by pyrogallic acid; the varnish which covers them being no disadvantage. The two ends of the induction wire are placed a little distance apart on the surface, and, according as it is more or less conductseconds or a few minutes. ing, the spark produces stratification on it in a few The strata are inflected towards the poles like stratified light in vacuo, with a characteristic difference by which the positive and negative poles can always be distinguished. Towards their extremities there takes place always a peculiar arborisation, and the bodies of the strata, examined under the microscope on the negative plate, seem formed of finer and more compact arborisations. By studying, for the purpose of finding them, the bands of light produced in a vacuum, some similar arrangement will perhaps be found; in fact, a sort of vibration is observable, which may result from each spark without effecting any change in the general form, producing a different arborisation. The stratifications always commence at the negative pole and extend progressively to the positive pole. The following experiment makes apparent this property of the them-negative pole:-The two ends of the induction wire being placed on a semi-conducting surface, withdraw from time to time the negative extremity. The spark, opening a way for itself, may thus extend to sufficiently considerable distances, and each point of stoppage of the negative wire is marked by an arborescent stratum, which continues to develope itself under the induced current. A different effect is produced by now and then withdrawing the positive wire, the negative wire remaining stationary. Permanent Stratification produced by the Spark of M. l'Abbé LABORDE. SEVERAL physicists have investigated the stratified light of the electric spark, and have assigned various causes for this curious phenomenon. The various researches on this subject have ended in establishing beyond doubt one Certain surfaces are very readily attacked by the spark. The stratifications are then more compact, and are produced from one pole to the other immediately. If the current is continued they are developed and encroach one upon the other; but although in the end confused, an experienced eye can still distinguish that they have existed. When the ends of the induction wire do not touch the surface, but project the spark to a distance, the design is not so easily produced, and presents a peculiar appearance. The stratifications are less marked and less arborescent. This is perhaps occasioned by the induction current on closing the circuit being suppressed, so that only the induction current formed when the circuit is opened exerts its action. The spark often deviates from the straight line, and when persisting to the right or left adds lateral stratifications to the principal figure. I have tried the spark of the ordinary electric machine, and found that it also produced transverse rays; but it penetrates with more difficulty than the induction spark, and remains long on the surface. An easily attacked surface should be selected, and the action should be prolonged so as to produce a sufficiently fine result. I used a mercury interrupter, which presents a special advantage; it is now known that the soft iron of the electro-magnet does not immediately acquire its full power, either because it opposes a certain resistance to magnetism, or because, in the first instance, the effect of the principal current is opposed by the counter current which it engenders. In automatic interrupters the contact is hardly established when it is broken by the attraction of the soft iron before it could attain the maximum of magnetism. In the interrupter about to be described, the part touching the mercury instead of severing from it by the attraction of the soft iron, sinks, on the contrary, still deeper, and severs from it an instant afterwards. It is composed of a small bar of soft iron, traversed in the centre by a horizontal axis on which it turns, presenting its extremities alternately to the soft iron of the electro-magnet. A small wheel fixed on the axis is furnished with two teeth inclined opposite to each other. These teeth, or small inclined planes, raise by turns the extremity of a lever oscillating on an axis, and plunges the other end in the mercury, upon which alcohol has been poured. The communication is thus properly effected; the excited electro-magnet attracts the superior end of the little bar, and before it has passed the line of force the inclined tooth escapes the lever, which is pushed by a spring away from the mercury. The same effect is produced when the bar presents its other extremity to the electro-magnet, and, if unopposed, assumes a very rapid rotatory movement. The induced sparks do not succeed each other so promptly as with the hammer interrupter; but they are more regular, brighter, and longer. I have modified the hammer interrupter in a way which renders it more efficacious. Its iron rod is surrounded with three layers of thick wire covered with silk; one of the ends is soldered to the head of the hammer, and the other is fastened by a moveable communication to the inducting wire towards the hinge at the handle of the hammer. The current then passes, not by the rod, but by the wire surrounding it, and is so directed that the hammer receives a contrary magnetism to that of the soft iron of the apparatus. The attraction becomes stronger, and in spite of the increased weight of the hammer more tension can be given to the spring pressing against the magnet. The result is more intimate contact and more complete action with each movement.-Comptes Rendus, lviii. 661. PHOTOGRAPHY. On the Application of Potassio-Ammonium Chromate to Photography, by M. E. KOPP. POTASSIO-AMMONIUM chromate, whether pure or with the addition of an ammonium salt, the acid of which may vary as the operator wishes, more or less, to modify the reaction, is an excellent photographic agent, since the It is espeundecomposed salt will not attack cellulose. cially useful for obtaining positive images from negatives prepared by the ordinary processes. The paper may be impregnated with a concentrated solution of the salt, and left to dry in the dark at the ordinary temperature without undergoing any alteration. time, and very gradually, that it assumes an orangeThe paper remains yellow, and it is only after a long yellow tint. It remains active for a considerable time. direct rays of the sun, the paper thus prepared soon But on exposure to daylight, and especially to the acquires a brown colour, becoming deeper and more intense. By covering the prepared paper with an engraving and then with a plate of glass, so as to press the engraving on to the paper, after a few minutes' exposure to the solar light, a very distinct negative image will appear. If the engraving is previously oiled, or an ordinary collodion negative is used, two or three minutes' exposure to the solar rays will produce a very defined effect. By washing the paper in pure water or acidulated with one or two drops of acid, the unaltered chromate is dissolved; the image is then fixed, and may, without fear, be dried in the light. The washing must not, however, be prolonged more than is absolutely necessary, if it is desired to preserve the characteristic yellowish-brown tint, nor must the picture undergo further treatment. There seems no doubt that potassio or sodio-ammonium chromate may advantageously replace bichromate of potash in all photographic processes in which the latter salt is used, as, for instance, in gelatine, carbon, &c., photographs. The reaction producing the image, and the behaviour of the latter, under considerably varied and interesting circumstances, may be easily explained. Under the influence of light the potassio-ammonium chromate loses its ammonia, becomes acid, and the chromic acid then reacting on the cellulose, partly oxidises it, and is, at the same time, reduced to brown chromic peroxide-CrO2. This peroxide CrO2=Cr ̧O ̧ — CrO„Cr2O, may also be considered as a chromate of chromium-that is to say, as resulting from the combination of chromic acid with green oxide of chromium, and, in fact, even with feeble affinities it is separated readily into chromic acid and oxide of chromium. NEWS with the lecturer's description of the optical characters of chlorophyll, the green colouring matter existing in plants. Although little is known as yet regarding the nature and composition of chlorophyll, the author considered there were sufficient grounds for believing that this green pigment was really made up of two separate principles, or kinds of colouring matter, which exhibited distinct optical properties; thus, one of the components showed in the spectrum a group of bands between F and G, whilst the optical character of the second body was much simpler. If green leaves were macerated for a short time with dilute alcohol the coloured infusion gave one band nearly coinciding with the line F, and another between F and G, but when bisulphide of carbon was used as the solvent the two bands were shifted nearer the red end of the spectrum to the extent of one band interval. If a mixed solvent were employed the group occupied an intermediate position; and the addition of an acid to the sulphide of carbon solution moved the bands back again to the same position as they were found to occupy in the alcoholic extract. The author then described the character of fluorescence as exhibited by quinine, "leaf green," fluor spar, and a variety of vegetable organic substances. When the bright rays of the sun or of the electric spark were allowed to fall upon the surface of an aqueous solution of a quinine salt, it was well known that a brilliant azureblue colour was developed, which made its appearance not only under the blue and violet portions of the spectrum, but extended from a point midway between the fixed lines G and H for a considerable distance into the chemically active, but otherwise invisible, part of the spectrum. The production of these blue rays was quite independent of a decomposition of light in the incident beam, and the author had already shown that their appearance was due to a change of refrangibility of the light always on the side of diminution; whilst with leaf-green infusion, which showed a red fluorescence, the alteration in the degree of refrangibility, still in the same direction, was made appa- | rent in a different manner. It was possible to observe simultaneously these optical effects, inasmuch as they occurred at different parts of the spectrum, if the precaution of taking a sufficiently diluted solution of the mixed substances were adhered to; that is to say, the absorption of the fluorescent light by too highly coloured a solution must of course in such a case be guarded against. By a series of coloured diagrams the author showed conclusively the manner in which he had proved fluorescence to be but the effect of a diminution in the degree of refrangibility, the blue rays of the solar spectrum were collected by a lens and passed throught a sufficient layer of the sensitive medium, the transmitted beam was then analysed by a prism and shown to consist of light of different degrees of refrangibility, but always inferior to that of the producing ray. The lecturer then proceeded to show some very beautiful experiments with a number of fluorescent substances, which were successively illuminated by the spark discharge of a Ruhmkorf coil, having a Leyden jar in circuit, and the power of window glass in cutting off the active rays was exhibited in comparison with a plate of quartz 4 inch in thickness. The latter did not in any appreciable degree obstruct the passage of the fluorescent rays, whilst the window-glass, no more than 1 inch thick, cut off nearly all. Among the substances thus experimented with were aesculin and fraxin, (the alkaloids contained in the bark of the horse-chestnut), purpurin from madder, which showed a yellow fluorescence, and solutions of terephthalic acid kindly furnished by Drs. De la Rue and H. Müller. The etherial solution of this last-named substance showed a bluish fluorescence, whilst the aqueous solution appeared green. By the optical examination of the permanganate of potash the lecturer discovered that the crystals by reflected light showed bands of maxima brilliancy exactly corresponding to the dark bands absorbed by the solution; it thus appeared that the crystallised salt partook of the optical characters of a metal and of a vitreous substance alternately. Similar quasi-metallic reflections were seen also in the platinocyanide of magnesium and in some of the crystallised aniline colours. In conclusion the author compared these results with the well-known observation that gold leaf showed a greenish hue by transmitted light, whilst it appeared of a rich yellow by reflected light; many other instances of notable variations in colour presented by chemical products would suggest themselves to his hearers. The PRESIDENT, in proposing a vote of thanks to Professor Stokes (which was warmly responded to), commented upon the importance to be attached to the lecturer's remarks, both as regards methods and results. Much had already been accomplished towards extending the means of physical observation, and no research would be considered complete unless it comprehended a statement of the optical characters of the substances in question. The speaker concluded by inquiring of Professor Stokes whether he was acquainted with any instance of a substance undergoing decomposition during the process of solution? Dr. ODLING asked whether any good explanation, founded on optical tests, could be assigned in the case of the wellknown fact that iodine when dissolved in alcohol or ether gave a brown solution, whilst with other solvents, particularly chloroform and bisulphide of carbon, the colour of the solution was violet? Whether there appeared to be any connexion between the mode of absorption characterised by iodine vapour and that of the bisulphide of carbon solution? Professor STOKES, in reply to the President, mentioned the fact of the green chloride of copper becoming blue on dilution; but, in answer to Dr. Odling's inquiry, said he was not prepared to give any theoretical explanation of the facts alluded to. The PRESIDENT requested, on the part of the Council, that Professor Stokes would be so good as to prepare an abstract of his communication for the purpose of being published in the Society's Journal. Dr. GLADSTONE suggested that if the lecturer would kindly enlarge upon the subject he had in so interesting a manner brought before them, he felt sure the Society would consider themselves even further indebted to Professor Stokes. The meeting was then adjourned until the 16th inst. CHEMICAL GEOLOGY, A Course of Twelve Lectures, by Dr. PERCY, F.R.S. Delivered at the Royal School of Mines, Museum of Practical Geology, Jermyn Street. LECTURE X.-Saturday, January 23. (Continued from page 248.) THE first carbonaceous deposit we shall consider is peat or turf. This substance has played a very important part in this country as a fuel, and is still extensively used, but it is much more valuable in other countries which do not possess those magnificent deposits of coal occurring in this country, and which are being so terribly misused, owing to a want of economy in the burning of the fuel. Of that we will speak hereafter. Peat is a product of the natural decay of various plants under special conditions of heat and moisture, and those special conditions occur in humid and temperate climates. Still we find peat in tropical regions, as I shall show you by-and-by. Immense accumulations of peat, as every one knows, exist in our peat-bogs in Ireland, and also in various parts of this country. It is abundant also in the central parts of France and other parts of Europe. It is found also in mountain declivities, where it seldom exceeds four feet in thickness. The peat of Europe is generally derived from mosses of the genus sphagnum-a very beau |