2 AßT 8.— S, NAKAMURA. 



to determine the numerical value of k for various substances. The 

 methods employed may be divided into two classes. In the first class, 

 the quantity of salt which passed through a given section during a 

 finite time was determined. To the second class belong those methods 

 in which the concentrations at different depths were determined ; the 

 latter methods are preferable to the former, for they give us clear in- 

 formation respecting the state of the diffusing liquid at any given 

 instant. A variety of methods were used by different experimenters. 

 Graham, Beez, (I) Beilstein, (2) Schuhmeister (3) and others determined 

 the quantity of salt passed through, or the concentration at any point, 

 from the density of the liquid ; Graham, and \Vroblewski (4) by evap- 

 orating the water out of the solution and weighing the salt left 

 behind. Long <5) and Scheffer (6) used titrimetrical methods. Wild 

 and Simmler (7 - ) who soon after the publication of Fick's paper, integ- 

 rated his equation, said that the concentration at any point could be 

 determined by a saccharimeter in the case of sugar. Hoppe- Seyler (8) 

 and Yait (9) used this method. \Vroblewski (10) and Wiedeburg (11) used 

 the photometrical method in colored solutions. Johannisjauz, (12) at the 

 suggestion of Kundt, used a liquid prism filled with the diffusing 

 liquid and determined the index of refraction at different heights. 

 AVcber fl3) employed an electrical method for determining the difference 



(1) Beez, Schlomilch Zeits. IV. 



(2) Beilstein, Ann. d. cheinie u. Pharm. 99. 



(3) Schuhmeister, Sitzungsber. d. k. Akacl. d. Wisseusch. zu Wien 79. 



(4) Wroblewski, Wied. Ann. 7. 



(5) Long, Wied. Ann. 9. 



(G) Scheffer, Zeits. für phys. Chemie, 2. 



(7) Wild and Simmler, Pogg. Ann. 100, 1857. 



(8) Hoppe-Seyler, Medieinisch-chemische Untersuchungen, 18G6. 



(9) Vait, Pogg. Ann. 130, 1867. 

 (L0) Wroblewski, lo2. sit. 



(11) Wiedeburg, Wied. Anu. 41, L890. 



(12) Johannisjawz, wied. Ann. 2, 1877- 

 (18) Weber, Wied. Ann. 7, 1879. 



