18 DIFFUSION AND OSMOTIC PRESSURE 



in the corresponding case with a liquid solute. Equilibrium 

 and an apparent stoppage of diffusion will be brought about 

 when diffusion is equal in both directions. 



III. SOLUTIONS OF SOLIDS IN LIQUIDS 



If a crystal of sugar or salt be put into the water, it dis- 

 solves. This process of dissolving consists in the flying off 

 of particles into the water, just as the process of vaporiza- 

 tion of a mass of naphthalene consists in the flying off of 

 particles into the air. After the particles of the dissolved 

 substance (solute) are once free from the solid mass, they 

 behave in an entirely different manner from that which 

 characterized them before. While they were in the crystal 

 they clung together by cohesion. Now they tend to sepa- 

 rate as much as possible within the limits of the solvent. 1 

 They may or may not pass the surface of the solvent and 

 enter the air as a gas, but within the solvent they continue 

 to diffuse until they are uniformly distributed. Diffusion 

 of the solute in its solvent takes place much more slowly 

 than does gas diffusion, but in the end it is just as com- 

 plete. Thus it is evident that within the volume occu- 



iT. GRAHAM, "Ueber die Diffusion von Flussigkeiten," Liebigs Ann., Vol. 

 LXXVII (1851), pp. 56-89 and 129-60; see also ibid., Vol. LXXX (1851), pp. 197-201. 

 The following references may serve to put the reader into contact with the 

 literature of diffusion : T. GRAHAM, " Supplementary Observations on the Diffusion 

 of Liquids," Phil. Trans. Roy. Soc. London, 1850, pp. 805-36; A. FICK, " Ueber Dif- 

 fusion," Pogg. Ann., Vol. XCIV (1855), pp. 59-86; T. GRAHAM, " Anwendung der Dif- 

 fusion der Flussigkeiten zur Analyse," Liebigs Ann., Vol. CXXI (1862), pp. 1-77; 

 F. VOIGTLANDER, " Ueber die Diffusion in Agargallerte," Zeitschr. f. physik. Chem., 

 Vol. Ill (1884), pp. 316-35; J. D. R. SCHEFFER, " Untersuchungen fiber die Diffusion 

 einiger organischen und anorganischen Verbindungen," I, Ber. d. deutsch. chem. 

 Gesellsch., Vol. XV (1882), pp. 788-801 ; II, ibid., Vol. XVI (1883), pp. 1903-17 ; W. NERNST, 

 " Zur Kinetik der in LOsung befindlichen KOrper," Zeitschr. f. physik. Chem., Vol. II 

 (1888), pp. 613-37; J. D. R. SCHEFFER, "Untersuchungen tiber die Diffusion wasse- 

 riger Losungen,"i6id., pp. 390-404; S. ARRHENIUS, "Untersuchungen iiber Diffusion 

 von in Wasser gelOsten Stoffen," ibid., Vol. X (1892), pp. 51-95 ; L. LIEBERMANN UND 

 S. BURGARSZKY., " Beitrage zur Theorie der wasserigen Losungen von Salzgemi- 

 schen," ibid., Vol. XII (1893), pp. 188-95; A. NACCARI, "Sulla pressione osmotica," 

 Atti delict Eeale Accad. del Lincei, Ser. 5, Rendiconti, Classe di Scienze fisiche, 

 matemat. e natural!, Vol. II (1893), 1 Semestre, pp. 238-9,' and 2 Semestre, pp. 136-8; 

 R. HOBER, " Ueber Concentrationsanderungen bei der Diffusion zweier gelOster 

 Stoffe gegen einander," Pflugers Archiv, Vol. LXXIV (1899), pp. 225-45. 



