32 GENERAL AND PHYSICO-CHEMICAL. 



as quickly into gels as into pure water. Nevertheless, SPIRO 1 has observed 

 that dissolved ovalbumin as well as haemoglobin could pass into gelatin 

 plates. On the other hand K. MEYER 2 as well as BECHHOLD and ZEIGLER 3 

 have found that the distance passed by a crystalloid in gelatin may be 

 much shorter than in pure water. In such experiments no doubt adsorp- 

 tion processes must be considered. 



m. CATALYSIS. 



When two bodies which can act chemically upon each other are 

 brought together the reaction generally takes place so fast that it can- 

 not be measured. In other cases, by special means, we can observe 

 how the reaction gradually proceeds. When cane-sugar is inverted 

 by weak acid, the decrease in the rotation of the solution can be fol- 

 lowed with the polariscope; and when an ester is decomposed by alkali 

 the quantity of still free alkali can be determined by titration. The 

 quantity of substance measured in gram-molecule per liter (mole) 

 which is decomposed in the unit of time, is called the reaction velocity 

 of the system. The so-called law of mass action, as proposed by GULD- 

 BERG and WAAGE, states that the reaction velocity is every moment 

 proportional to the molecular concentration of the reacting bodies. A 

 mixture of alcohol and acetic acid is transformed into acetic ether and 

 water, especially in the presence of some mineral acid. If the molec- 

 ular concentration of the alcohol and acid be designated by C A and C s , 

 then according to the law of mass action the reaction velocity is 

 Vi=ki.C A -C s , where k\ indicates a constant which is independent of 

 the quantity of reacting substances and the time limit is so short that 

 the concentration can be considered as constant. This reaction, like 

 many others, is reversible, 4.e., two reactions occur simultaneously: 

 one between the alcohol and acetic acid, producing acetic ether and 

 water, and second, between acetic ether and water, re-forming alcohol 

 and acetic acid. This is expressed as follows : 



The velocity of reaction when it passes from left to right is called 

 v\. If the velocity in the reverse reaction is called V2 and the molecular 

 concentration of the acetic ether and water is called C B and C w , 

 then we obtain V2 = k2-C E 'C w . At the beginning when C E as well as 



1 Hofmeister's Beitrage, 5, 294 (1904). 



2 Ibid., 7, 393 (1905). 



3 Zeitschr. f. physik. Chem., 56, 105 (1906). 



