(504 EXPERIMENT STATION RECORD. 



tliiis: The allyl i;Tonp becomes a propyleii groiq), bnr it is not possible 

 to change the propyleii ^i^rouj) to the allyl ^roup. The allyl comiwiuids 

 are unstable, in comparison with the propylen compounds. In proof of 

 this the heat e(piivalent of the two compounds O10H12O2 is: 



C:il(iries. 



Eugciinl, allvl-dioxy-benzin-mono Diethyl etlier 1,286.9 



Isoeii^eno], i)ropylen-flioxy-benzin-mouo-metbyl ether 1,278.1 



A number of other instances of this sort may be cited.' 

 All the cases wiiicli have been mentioned (and there are very many 

 more) have been grouped together under the general head of catalytic 

 reactions, but no satisfactory explanation has been given up to this time. 

 Thermochemistry has here filled up one gap in scientific knowledge. 



If we consider what conditions are necessary to bring about a cat- 

 alytic reaction we find we can distinguish two: 



(1) Only those molecules which are in unstable equilibrium are 

 subject to catalytic change. In hydrogen peroxid, the classic exam- 

 ple of a catalytic reaction, the molecule is in the highest degree 

 unstable. The atoms rearrange themselves with the greatest ease, 

 forming molecules of water and oxygen. In the sugar molecule, the 

 atoms are unstable; they change easily to the more stable molecules, 

 alcohol and carbon dioxid. The disaccharids, the tri and polysaccha- 

 rids are unstable in comparison with the hexoses, and are easily 

 changed into these. In the ethers of the mon-atomic alcohols the 

 atoms are in unstable equilibrium. They easily take on the elements 

 of water and form acids and alcohols. The cases of maleic and 

 fnmaric acids and of allyl and propylen compounds were cited above. 

 All these processes have one thing in common — they are without 

 exception accompanied by a loss of energy. 



(2) Catalytic reactions take place only in the presence of a second 

 compound, which does not necessarily enter into the reaction, or they 

 take place under the influence of some form of energy, the quantity 

 being very minute. 



The catalytic process which has been most thoroughly studied is the 

 alcohol fermentation, which takes place through the agency of the 

 alcohol ferment, the yeast plant or Saccharomyces. This, according to 

 Pasteur, is to be explained as a i)hysiological process of the yeast plant. 



It is evident that this explanation does not " explain," but only states 

 the same facts in a difterent way. 



Liebig^ looked at all fermentations from one general standpoint. He 

 considered the ferments to be substances undergoing chemical change. 

 The atoms in the molecules were in a state of violent agitation, and this 

 motion tended to produce structural change. They could impart this 

 motion to those substances which were capable of undergoing fermenta 



' Ber. math.-phys. Klasse kgl. s'ichs. Ges. Wisseiisch. Leipzig, 1892, p. 307; Jonr. 

 prak. Chem., 2d ser., 46, p. 530. 



'^Org. chem. in Anwendung auf Agricultur n. Physiol., 1810, j). 199. 



