Resolved, That Mr. Green be invited to meet the Committee at the next

meeting.

Resolved, That Admiral FitzRoy and Mr, Glaisher be added to the Committee,

Burlington House, 15 July, 1859.

Present, Colonel Sykes in the Chair, Lord Wrottesley, and Admiral FitzRoy. Read a letter from Professor Tyndall, regreting his inability to attend the meeting, but offering his services to ascend in the balloon, and assist in the observations.

Mr. Green attended, and stated that himself and his balloon were at the disposal of the Committee whenever called for.

Colonel Sykes reported that the following gentlemen offered their services to ascend with the balloon as observers: Mr. E. B. Russell, and Mr. John Murray, students of medicine in Glasgow University, Mr. Storks Eaton of Dorsetshire.

Resolved, That Colonel Sykes apply to the Chairman of the Kew Committee to have the instruments used in the former balloon ascents prepared for immediate use.

Resolved, That Colonel Sykes be authorized to make the necessary arrangements with the several parties to be employed, preparatory to ascents which may take place either from Birmingham or Wolverhampton. Consequent upon the above resolution, Colonel Sykes arranged the terms of compensation with Mr. Green for four balloon ascents-the first £30, the second £25, the third £20, and the fourth £15, the Committee paying for gas, and all incidental expenses. Lord Wrottesley was good enough to obtain a supply of gas from the Wolverhampton Gas Company, the use of their yard for the ascents, and the cordial assistance of their people. Monday, the 15th of August, was fixed for the ascent; and Mr. Storks Eaton, who had previously taken charge of, and made himself familiar with, the instruments, offered his gratuitous services to go up in the balloon. Lord Wrottesley, Admiral FitzRoy, Mr. Glaisher, and the Chairman assembled at Wolverhampton, at 1.30 P.M., to superintend the ascent. The weather was fine, but the wind came in gusts; the inflation, however, commenced; but the balloon filled slowly, and when 63,000 cubic feet of gas had been introduced, the evening was fast approaching; and as doubts were expressed of the ascent being made in safety, in consequence of the wind, the Committee resolved to defer the ascent until the following day.

On Tuesday, the 16th of August, the Committee assembled at 1.20 P.M.; the balloon had been completely inflated; but as the Committee were entering the Gas Company's yard, a gust of wind occasioned the neck of the balloon to flap so violently, that a rent of some yards was produced, and the gas escaped rapidly. This untoward accident stopped all further proceedings; and as Mr. Green said that the balloon could not be properly repaired within many days, as the balloon had received other injuries, the Committee were compelled to forego any attempt to effect balloon ascents before the approaching meeting of the British Association.

The Committee having thus reported their proceedings, recommend the reappointment of the Committee to carry out the objects which an accident has frustrated; and the Committee look to the concurrent opinions of the distinguished men who have expressed themselves favourable to further balloon ascents, having their due weight.

The Committee cannot close their report without expressing their oblig tions to the Mayor of Wolverhampton, Mr. John Hartley, and to the Di

rectors of the Gas Company, for their courtesy and cooperation. The thanks of the Committee are particularly due to Lord Wrottesley for his active and efficient aid, and for the reception of the Members under his hospitable roof at Wotesley Hall.

London, 20th August, 1859.

W. H. SYKES,

Chairman.

P.S.-Mr. Green not having fulfilled his engagement, was only paid his incidental expenses

Gas

Expenses of Committee

Mr. Eaton's carriage of instruments and ether

Total ....

£ 7 5 11

20 5 0

Preliminary Report on the Solubility of Salts at Temperatures above 100° Cent., and on the Mutual Action of Salts in Solution. By WILLIAM K. SULLIVAN, Professor of Chemistry to the Catholic University of Ireland, and the Museum of Irish Industry.

NOTWITHSTANDING the evident importance of the phenomena of solution, not only in a purely physical and chemical point of view, but also in connexion with many of the most interesting geological and physiological phenomena, the subject, until recently, seems to have been almost altogether neglected, as if by common consent. Our knowledge respecting the solubility of any given substance in certain liquids, was usually comprised in such expressions as "soluble," " very soluble," " difficultly soluble," &c.-I might even say, is now comprised; for the law of solubility in water up to the temperature of 100° Cent. can scarcely be said to be known for a dozen salts, and has not been at all determined for higher temperatures or for other solvents. Since the admirable experiments of Gay-Lussac, by which he established the law of solubility of Glauber-salt, many important investigations, bearing upon the subject of solution, have no doubt been published; but, generally speaking, the immediate objects of these researches had to do with some other department of physics or chemistry, rather than with the establishment of a theory of solution. Among these I may mention Legrand's experiments on the influence of salts on the boiling-point, Frankenheim's on the capillarity of saline solutions, the well-known researches of Graham on the diffusion of solutions, of Person, Favre and Silbermann, Andrews, &c., on the latent solution heat of salts, Playfair and Joule's researches on atomic volume, and many others which it is needless to mention. Any experiments directly bearing on the subject which did happen to have been made with the view of determining numerical laws, were in general confined to the determination of the quantity of salt held in solution at different temperatures, and to the specific gravity of the solution. The range of temperature was usually limited to that between 0° and the boiling-point of the solvent, or to that of the dissolution. The uncultivated state of this important field of inquiry is no doubt to be attributed in part to the great labour required to work it, and the apparent insignificance of the results of even the most successful research. The recent laborious investigations of Löwel, Kremers, Gerlach, Wullner and others, show, however, that it is no longer likely to remain uncultivated; and from the enlarged views of the general physical relations

of the phenomena of solution which these experimenters exhibit, we may expect most important results from their labours.

The graphic coordination of the results of experiments on the solubility of salts which have hitherto been recorded, lead to this capital fact, that within the limits of temperature embraced by the experiments, soluble salts may be classified into three groups :-1, those which, like sulphate of soda, attain a maximum of solubility within those limits, that is, give an ascending and descending curve; 2, those which, like common salt, have sensibly the same solubility at all temperatures within the limits; and 3, those which, like nitrate of potash and the majority of salts, increase considerably in solubility as the temperature rises. The fact of certain salts, such as sulphate and carbonate of soda, exhibiting a point of maximum solubility, or, as Löwel has shown, several such points, according to the modifications which take place in their molecular states, naturally suggests the probability that most salts would exhibit a point or points of maximum solubility, and a descending as well as an ascending curve of solubility, if we were to extend the range of our experiments to sufficiently high temperatures, provided they could resist without decomposition or volatilization such temperatures. And further, that many salts more or less soluble at common temperatures, may become wholly insoluble at high temperatures. In the case of sulphate of lime, the latter fact has been established by the observations of M. Couche and myself. From some preliminary experiments which I have since made, I think I shall be able to establish it in the case of many other salts likewise. Although water under sufficient pressure retains its liquid form at tenperatures far above 100°, the experiment of Cagniard de la Tour shows that if the temperature be raised sufficiently high cohesion will ultimately disappear, and the water will pass without alteration of volume into gas of enormous tension. Frankenheim and Brunner have both found that the elevation of water in capillary tubes decreases with the temperature, and that it is capable of being represented by a very simple formula of interpolation as a function of the temperature. If this formula were to hold approximately true at very high temperatures, it would enable us to trace the diminution of the cohesion as the temperature rises, until it would wholly vanish, which on this hypothesis would take place, according to Brunner, at 535-38. Cagniard de la Tour made similar experiments upon some other liquids with like results. He found that the total gasification of ether took place at about 200°. The temperature at which the capillary height of ether would be zero, calculated by Brunner's formula, would be 191° 12. Wolf has experimentally found that the capillary height was reduced to zero at 190° or 191°; above that temperature the capillary meniscus was below the level of the liquid, that is, there was capillary depression. At about 198° the strongly convex surface of the liquid appeared to cover itself with a thick cloud at about 200° it was wholly changed into vapour. This striking coincidence between the calculated and experimental results, M. Wolf considers to be only accidental. Brunner's formula was founded upon experiments made within the limits of temperature of 0° to 35°, a range which M. Wolf thinks too limited. He has found, that, although the law of Brunner, that the decrease of the capillary height is proportional to the temperature, holds true up to 100°, it becomes more rapid above that point. Whatever may be the exact law for high temperatures, enough has been done to show that the decrease of capillarity may be employed as a measure of the diminution of cohesion at high temperatures. I think we may safely con

* Ann. de Chim. et de Phys. vol. xlix. p. 230.

clude, both from Cagniard de la Tour's experiments and the theoretical results of Frankenheim and Brunner, that at a red heat water would be completely gasified. If instead of pure water we subject a saline solution to a high temperature, what would be the result? Long before the solution would attain the temperature at which water would pass into gas of the same volume, it seems probable that a large number of salts would become insoluble, owing to the gradual diminution of cohesion between the molecules of water. If this supposition be correct, the point of maximum solubility of a great many salts cannot be higher than 200° Cent. At very high temperatures water is capable of decomposing a large number of salts, even otherwise very stable double silicates; but as this action appears to depend in many instances upon the mass of the water, saturated solutions of salts heated under pressure, are not so liable to be decomposed as when salts are exposed to a current of hot steam. If the salt did not become insoluble before the water reached the point of gasification, and that it was capable of resisting that temperature without decomposition, and was not per se volatile at a red heat, we may conclude from the slight affinity between gases and solids, as well as from many other considerations, that the water and salt molecules would completely separate. The singular anomaly which boracic acid offers of being volatile in the vapour of water, a property which the experiments of Larocque * show belongs to many other fixed substances, also indicates that possibly several salts may not precipitate on the passage of the water into gas, but remain attached to the gaseous molecules. Under such conditions of temperature and pressure the most unforeseen phenomena may be presented to us.

The study of the laws of solubility of salts at very high temperatures is obviously, then, of very considerable importance. In undertaking their investigation I did not underrate the difficulty of the subject, though perhaps I did its extent. The most superficial consideration will at once convince any one that a mere table of the quantities of salt held in solution at different temperatures would be of very little value; and that, to be of any use, the investigation should include that of the action of salts in solution upon one another at those high temperatures. Further, as the study of the solubility of salts at any given temperature is but a particular case of the general question of solution, every such investigation must necessarily deal more or less with the whole of the phenomena of solution. The problem I proposed to investigate, while apparently limited enough, involves in fact the study of a very considerable branch of the physics of molecules. In so extensive a field of inquiry, and especially where we have to deal with very complicate phenomena, the study of which is beset with practical difficulties, and even danger, the individual investigator cannot hope to reap a very large return for his labour, however successful he may be. Every one who has worked at such subjects will understand that considerable progress must be made in an investigation of this kind before the results admit of being coordinated. Notwithstanding many unexpected interruptions, I have devoted a good deal of time in preliminary experiments upon the best methods of conducting my researches, and in endeavouring to devise apparatus for the purpose. Even though my progress were very rapid, instead of being very slow, as it has been, I should not be in a position to bring before you on this occasion a report of any numerical results which I may have obtained. It is due, however, to the Association to explain in a short preliminary report the point of view from which I am proceeding, and the extent and character of the field of research. As in so extended a subject any results obtained during the inquiry must be communicated piecemeal, such a preliminary report may

* Journ. de Pharm. vol. xiv. p. 345.

serve hereafter the very useful purpose of linking them together and indicating their relative importance until a final report can be drawn up.

In considering the subject which I propose to investigate, several questions immediately suggest themselves, which demand attention before entering upon the inquiry itself, as they relate to matters which constitute the groundwork of the whole subject. Of these I shall mention a few :-1. What is solution, and in what does it differ from fusion? 2. What special function does the solvent perform, and in what do water, alcohol, ether, and carbides of hydrogen differ in their solvent functions? 3. In what relation does water of crystallization stand to the other constituents of a hydrated salt? 4. When hydrated salts are dissolved in water, does the saline water still remain attached to the salt molecule, or does it mingle with the solvent? Or, in other words, in considering the physical properties of saline solutions, are we to regard them as made up of water molecules and anhydrous salt molecules, or as water and complex molecules of hydrated salts?

These questions have not been answered. No satisfactory hypothesis has even been proposed for the purpose. Neither can we hope to do so before the whole subject of molecular physics shall have considerably progressed beyond its present imperfect state. Still, although we cannot hope to answer those questions fully, they are so important in connexion with the special object of the present investigation, that they must necessarily be included as far as possible with it.

Many are inclined to consider solution as a case of chemical combination. In adopting this view, we do not, however, solve the problem; but if suffi cient grounds existed for adopting it, we may consider doing so a step in advance, inasmuch as it would save us from the necessity of inventing a new form of force. If the test of chemical combination be, that the combining bodies unite in definite proportions, solution appears at first sight not to possess that characteristic. It appears to me, however, that we ought to distinguish two kinds of solution :-1, that of liquids in liquids; and 2, of solids in liquids. Some considerations founded upon the dynamical theory of heat may help us to understand this distinction.

According to that theory, the molecules of gases are so far separated as to be beyond the sphere of their mutual attractions, and they are further considered to travel onwards in straight lines according to the ordinary laws of motion. A gas may therefore freely flow into another, there being no cohesion between the molecules, and chemical attraction only when molecules which are strongly polar approach within the sphere of their attractive forces. In liquids, on the other hand, the repulsive action of motion is not sufficient to remove them beyond the sphere of their mutual attraction, notwithstanding that each molecule has not a determinate position of equili brium, and may consequently freely change its place.

The liquid molecules are, in fact, assumed to be in a state of vibratory, rotatory, and progressive motion, so that each molecule is not permanently attached to another; but the progressive motion is not sufficient to carry it beyond the cohesive influence of the others. We may assume that great differences exist in the character and velocity of the vibratory and rotatory motions of the molecules of different fluids. The fluids, the molecules of which possess the same character of motion, may consequently mingle, because the molecules of each will not interfere with each other's motion. When the motions of the molecules of two fluids are incompatible, they do not mingle. The observations of Wilson and Swan upon the changes which one liquid produces in the form of the surface of contact of another, appear to support the view just stated.