434 



F'rom an experiment with nndecanic acid it appeared that this 

 substance indeed, flocked out the sol in 807o alcohol. 



Now a flocking-out need not necessarily cause a paralysis ; but 

 as the first phenomenon is a visible indication of the diminution of 

 the surface of the catalyser it is most probable that in this instance 

 the decrease of the velocity of reaction is related to the flocking-out. 

 It stands to reason that in determining the velocities of hydration, 

 the possibility of the paralysis must always be reckoned with, and 

 that any cases in which flocking-out sets in are of but little value 

 for the comparison of these velocities. 



We consequently give a short summary of the substances, which 

 at a normal temperature immediately or after a short time completely 

 flock-out the Pd-sol : 



in aqueous solution : diluted HCl, diluted KOH ; in SO"/, alcohol 

 undecanic acid, cinnamic acid, phenol, acrylic acid metliylester, iso- 

 crotonic acid, oleic acid, glacial acetic acid, propionic acid, butyric 

 acid, valeric acid, capric acid, caproic acid, lauric acid, palmitic 

 acid. 



On the other hand the sol remained unchanged for a considerable 

 time : in aqueous solution on the addition of diluted sulphuric acid, 

 acetic acid to 807o. diluted soda, undecylenic acid, undecylenic acid 

 aethylester, cinnamic acid methyl- and aethylester. Diluted nitric 

 acid dissolved the nietal. 



On summarising the phenomena described in these pages, we 

 undoubtedly get an idea, that even in this apparently so simple 

 catalytic reduction, viz. an irreversible reaction with an elementary 

 catalyser, the events are far more complicated and far more sensitive 

 to by-circumstances than could be expected. 



Not until these events have been sufficiently studied, so that they 

 can be entirely brought under the control of the experiment, can 

 a mathematical treatment produce good results. 



