On the Direct Correlation of Mechanical and Chemical Forces. 145 



The Bakerian Lecture. — " On the Direct Correlation of Mecha- 

 nical and Chemical Forces." By Henry Clifton Sorby, F.R.S. 



Perhaps it may be thought somewhat strange that a geologist should 

 undertake such a subject as the correlation of forces ; but the very 

 fact of my being a geologist has led to the investigations of which 

 I now purpose to give a short preliminary account. In studying 

 general chemical and physical geology, and especially in examining 

 the microscopical structure of rocks, I have for a number of years 

 been greatly perplexed with a class of facts which pointed both to a 

 mechanical and to a chemical origin. At first I attributed them either 

 to a mechanical or a chemical action, or^to the two combined ; but in 

 most cases no satisfactory explanation could be given. At length, 

 however, facts turned up which altogether precluded any supposition 

 not involving direct correlation ; for they most clearly indicated that 

 mechanical force had been resolved into chemical action in the same 

 way as, under other circumstances, it may be resolved into heat, 

 electricity, or any other modification of force, as so ably described by 

 Grove in his work 'On the Correlation of Physical Forces/ 



The effect of pressure on the solubility of salts has already been 

 made the subject of speculation and experiment *, and a considerable 

 number of facts have been described, showing that pressure will more 

 or less influence such chemical actions as are accompanied by an 

 evolution of gas, so that it may cause a compound to be permanent 

 which otherwise would be decomposed!; but the results were for the 

 most part so indefinite and unconnected, or of such a character, that 

 Mr. Grove does not allude to the direct production of chemical action 

 from mechanical force. That this is, however, extremely probable 

 will be evident to all who have considered the manner in which the 

 various physical forces are correlated ; for if mechanical force can be 

 produced by chemical action, why should not the converse be true ? 

 In this paper I shall endeavour to show that such is really the fact, 

 and that in some cases the mechanical equivalent of the chemical force 

 may be determined. 



In order to obtain the necessary great pressure, I have made use of 

 a modification of the method employed by Bunsen ; but instead of 

 filling the tubes at the ordinary temperature of the atmosphere and 

 then gently heating them for several hours, I in the first instance filled 

 them at a temperature 10° or 20° C. lower, so that when finally 

 sealed up they contained considerably more liquid than they could 

 hold without pressure at the ordinary temperature of the atmosphere 



* Perkins, Ann. de Chira. et de Phys. vol. xxiii. p. 410. Sartorius von Walters- 

 hausen, Gottinger Studien, 1857. Bunsen, Ann. der Chem. und Pharm. 1848, 

 vol. lxv. p. 70. Favre, Comptes Rendus, vol. li. p. 1027. Thomson, Proc. Roy. 

 Soc.vol. xi. p. 473 (1861). 



t Sir James Hall, Trans. Roy. Soc. Edinb. 1812, vol. vi. p. 71. Wohler, Ann. 

 der Chem. und Pharm. vol. xxxiii. p. 125. Babinet, Ann. de Chim. et de Phys. 

 (2) vol.xxxvii. p. 183. Lothar Meyer, Pogg. Ann. vol. civ. p. 189. Beketoft", 

 Comptes Rendus, vol. xlviii. p. 442. Gassiot, Brit. Assoc. Report, 1853, p. 39. 

 Favre, Comptes Rendus, vol. li. p. 1027. Berthelot et Pean de Saint-Gilles, 

 L'Institut, 1862, p. 257. Gmelin's Handbook of Chemistry, published hy the 

 Cavendish Society, vol. ii. p. 293. 



Phil. Mag. S. 4. Vol. 27. No. 180. Feb. 1864. L 



