Nov. 4, 1886] 



NA TURE 



inents referred to in Rankine's "Civil Engineering," it may be 

 said that the average strength of Fujisan lies between that ol 

 rubble work and sandstone ; Iwakisan, Nantaisan, and Alaid 

 are like good rubble masonry, while the strength of the ill-fated 

 Krakatao is not much above that of ordinary brickwork. 



8. Theoretical Mountains.— \i it might be interesting to com- 

 ])are actual mountains with theoretical mountains constructed 

 from the equation — • 



:(- 



such mountains have been drawn, and are shown in Fig. 2. The 

 values of c are given in the following table. 



In drawing up the table the instantaneous breaking strength 

 of granite and its crumbling strength, which is the largest pos- 

 sible value for k, are taken as being equal. For sandstone the 

 crumbling strength is assumed to be three-fourths of the break- 

 ing strength, while for rubble work and brickwork it has been 

 taken as one-half. 



^ _ ik 



P 

 18,500 

 8,200 

 2,500 

 1,300 

 i 48,000 



Instant; 



Material breaking strength 



in lbs. square feet 



Granite 1,584,000 



Sandstone 790,000 



Rubble masonry ... 316,000 

 Brickwork 144,000 



Crumbling 

 trength or 

 k in lbs. 

 ,580,000 

 590,000 

 150,000 

 72,000 



Weight 

 cubic 



foot lbs. 

 170 

 144 

 120 



H2 



Sandstone 14,500 feet 



Granite 20,000 ,, 



The diameter of the base of each of these mountains 

 feet, and the height to which mountains of the following different 

 materials could be built upon such a base without crushing would 

 approximately be : — 



Brickwork 4,600 feet 



Rubble masonry .. 7,300 ,, 



9. Causes Modifying Volcanic Forms. — Causes modifying the 

 natural curvature of a mountain are :— 



(i) The tendency during the building up of the mountain of 

 the larger particles to roll farther down the mountain than the 

 smaller particles. 



(2) The effects of atmospheric denudation, which carries 

 materials from the top of the mountain down towardi the base. 



(3) The position of the crater, and the direction in which the 

 materials are ejected. 



(4) The existence of parasitic craters on the flanks of a 

 mountain. 



(5) The direction of the wind during an eruption. 



(6) The sinking of a mountain in consequence of evisceration 

 beneath its base. 



(7) The expansions and contractions at the base of a mountain 

 due to the acquisition or loss of heat before and after eruptions. 



10. EJtict of Volcanic Eruptions on the People. — The erup- 

 tions in Japan from time to time have exerted a very marked 

 influence upon the minds of the Japanese people. Divine in- 

 terference has been sought to prevent eruptions, priests have 

 been ordered to pray, taxes have been repealed, charities have 

 been instituted, special prayers against volcanic disturbances 

 have been formulated, and have remained in use for the period 

 of loo years, %\ hile special days for the annual offering up of 

 these prayers have been appointed. At the present day a form 

 of worship to mountain deities is not uncommon. 



SOLUTION^ 

 Opening of the Discussion ly Prof. Tilde n 

 "C"OR want of time, the consideration of various phenomena 

 ■'■ connected with the subject was necessarily omitted. Thus 

 no reference could be made to the various formula relating to 

 expansion or density of solutions, nor to their optical properties, 

 magnetic rotation, nor to the subject of electrolysis. In what 

 follows, a review is presented of the principal phenomena ob- 

 served in the act of solution of solids (especially metallic salts 

 and other comparatively simple compounds) in liquids, and the 

 chief properties of the resulting solutions, with the object of 

 arriving (if possible) at some conclusion as to the physical ex- 

 planation of the facts. The question must at^once arise whether 

 these phenomena are to be considered as chemical or mechani- 

 cal, and all the theories which have been put forward to explain 

 the nature of solution are roughly divisible into two classes, 

 according as, on the one hand, they represent the process as a 

 kind of chemical combination, or, on the other, explain the 



ngha 



neeting of the British Asso- 



phenomena by reference to the mechanical intermixture of 

 molecules, or by the influence of the rival attractions of cohcsi.. n 

 in the solid and liquid, and of adhesion of the solid to the liquid. 

 The former hypothesis seems to have been universally adopted 

 by the older writers, such as Henry and Turner, and it seems 

 pretty clear that Berthollet also regarded solution as an act 

 of chemical combination. Among modern chemists, Prof. 

 Josiah P. Cooke takes a similar view, but M. Berthelot is the 

 most consistent and powerful supporter of the same hypothesis. 

 In his " Mecanique Chimique," tome ii. p. 160, will be found 

 a very clear and formal statement of the views upon this subject 

 which, it is interesting to know, are retained by M. Berthelot 

 without modification in any essential particular. 



On the other hand, there are a number of writers who, whilst 

 referring the phenomena of solution to a molecular attraction of 

 some kind, do not attribute solubility to the formation of che- 

 mical compounds of definite composition. Graham distinctly 

 ranges himself on this side. Brande also appears to have taken 

 a similar view ; Daniell, iMiller, Nicol, and Dossios may be 

 more or less ranked with them. A theory differing in some im- 

 portant respects from those of the above writers was briefly 

 enunciated in a paper communicated to the Royal Society by 

 Tilden and Shenstone in 1883. In discussing the connection 

 between fusibility and solubility of salts, the authors point out 

 that the facts tend to "support a kinetic theory of solution, 

 based on the mechanical theory of heat. The solution of a soUd 

 in a liquid would accordingly be analogous to the sublimation of 

 a solid into a gas, and proceeds from the intermixture of mole- 

 cules detached from the solid with those of the surrounding 

 liquid. Such a process is promoted by rise of temperature, 

 partly because the molecules of the still solid substance make 

 longer excursions from their normal centre when heated, partly 

 because they are subjected to more violent encounter with the 

 moving molecules of liquid." This theory, however, only 

 relates to the initial stage of the process of solution, and does 

 not sufficiently explain saturation nor the influence of dissolved 

 substances upon vapour-pressure, specific heat, specific volume, 

 &c. How far is it true that evolution of heat indicates chemical 

 combination : does the evolution of heat which often takes 

 place on dissolving a solid in water, or on adding more water to 

 its solution, indicate the formation of hydrates, i.e. compounds 

 of the dissolved body with water in definite proportions? 

 Thomsen answers this question in the negative (" Thermo- 

 chemische Untersuch.," Band iii. p. 20). 



Take the case of sulphuric anhydride (SO3). It is evident 

 from the diagram exhibited that more than half the total evolu- 

 tion of heat occurs on addition of the first molecule of water to 

 the solid substance ; yet the succeeding molecules give quite an 

 appreciable thermal change. At what point in such a curve 

 should we be justified in setting up a distinction between the 

 effect due to chemical combination and that due to other causes, 

 such as the change of volume consequent on dilution or the 

 possible loss of energy from the adjustment of the motion of the 

 molecules of the constituents to the conditions requisite for the 

 formation of a homogeneous liquid, or (though not in the present 

 case) the decomposition of the compound by the water? In the 

 act of solution of the sohds, and especially of anhydrous salts in 

 water, the volume of the solution is always less than the sum of 

 the volumes of the solid and its solvent, with the exception of 

 some'ammonium salts in which expansion occurs. Similarly the 

 addition of water to a solution is followed by contraction. 1 his 

 contraction may be due to mere mechanical fitting of the mole- 

 cules of the one liquid into the interspaces between the mole- 

 cules of the other (see Mendelejeft''s abstract in Journ. Cheni. 

 Soc, Feb. 1885, p. 114). This would probably not be attended 

 by loss of energy. Or the contraction may arise from tu. 

 readjustment of molecular motion already referred to. 



If we know the coefficient of expansion of the liquid and its 

 specific heat, we can calculate the amount of heat evolved for a 

 given contraction. If this is done for sulphuric acid, and many 

 other cases, it is found that, after accounting for the thermal 

 change due to alteration of volume alone, there is a surplus of 

 heat evolved which may really indicate some kind or some 

 amount of chemical combination. 



Thomsen has found that as a rule the heat of solution and of 

 dilution are both either positive or negative. Of thirty-five 

 salts examined, only four supply well-marked exceptions. How- 

 ever we may ultimately explain the anomaly exhibited by these 

 salts, the fact remains that the heat evolved or absorbed during 

 the admixture of any substance with water is in every case a 

 continuous function of the quantity of water added. Similarly 



