Absorbed on contact of Liquid with Solid. 241 



in water at a temperature below 4° C, a rise of temperature 

 is observed, and he accordingly rejected the physical hypo- 

 thesis of surface pressure, and adopted a chemical or physico- 

 chemical hypothesis which had been advanced by Cantoni *, 

 and which has been more fully developed by Martini f. It 

 has, however, been pointed out that the experiments of 

 Meissner do not disprove the validity of the hypothesis of 

 surface pressure, for as the pressure increases the point of 

 maximum' density of water is lowered, and at a pressure 

 of about 200 atmospheres the point of maximum density 

 of water is at or near 0° 0., as shown by Tait, Amagat, 

 Lussana, and others J. 



Lagergren § has shown that the pressure at the surface c f 

 silica and water would, from the above equation, amount to 

 some thousands of atmospheres. 



Martini, on the other hand, is unwilling to admit such an 

 enormous pressure at the surface, and he supposes that, just 

 as some solids are dissolved by liquids and thereby become 

 liquid, so liquids are absorbed by powders and thereby 

 become solid, the heat evolved being equivalent to the latent 

 heat which the liquid gives up in solidifying. 



Other investigators who have made experiments on the 

 Pouillet effect and allied phenomena are Tate ||, MelsensH, 

 Chappuis **, Wiedemann and Liideking ff, Gore J J, Erco- 

 lini §§, Bellati ||[|, and Linebarger ^[H. 



In Gore's experiments, a powder such as silica or alumina 

 was dropped from the air into water which contained some 

 soluble salt ; the liquid was not stirred, and the temperature 

 observed was that of the powder which sank to the bottom of 

 the liquid. The object of these experiments was to discover 



* Cantoni, Rend, del R. Istituto Lombardo, viii. p. 135 (1866). 



t Martini, Atti del R. Istituto Veneto, viii. (1896) ; ix. (1897) ; xii. 

 (1900). 



X Tait, Proc. R. Soc. of Edinburgh, 1881-82, 1882-83; Marshall, 

 Smith and Omond, Proc. Roy. Soc. Edinburgh, 1881-82; Aniao-at, 

 Comptes Rendus, cxvi. p. 946 (1893) ; Lussana, Nuovo Cimento (4) ii. 

 p. 233 (1895). 



§ Lagergren, Kongl. Vetenskaps Akademiens,l$. 24, Afd. ii., Stockholm, 

 1899. 



|| Tate, Phil. Mag. [4] xx. p. 508 (1860). 



5!" Melsens, Memoires dp. tAcademie de Belgique, xxiii. (1873) ; Ann. 

 de Chim. et de Phys. [5] iii. p. 522 (1874). 



** Chappuis, Wied. Ann. xix. p. 21 (1883). 



ft AViedemann and Liideking, Wied. Ann. xxv. p, 145 (1885). 



%X Gore, Phil. Mag. xxxvii. p. 306 (1894) ; Birm. Phil. Soc. Proc. 

 vol. ix. pt. 1 (1893). 



§§ Ercolini, Nuovo Cimenti, Serie 4, vol. ix., Feb. 1899. 



|| || Bellati, Atti del R. Istituto Veneto, Tomo lix. Parte Seconda, 1900. 



^1H Linebarger, Physical Review, vol. xiii. No. 1, July 1901. 



Phil. Mag. S. 6. Vol. 4. No, 20. Aug. 1902. R 



