( 67 ) 



reaction at 445° is also a unimolecHlar one and llial lliorcfore tlie 

 observations of Sciienck and Zimmkrmann must he fault v as far as 

 the temperature 445° is concerued. 



Ex])('nment. 



In order that the reaction might not take place too rapidly the 

 reaction vessel was now filled one third with the catalyser (pumice- 

 niekel-carbon) ^). 



The object of the first experiments was to determine the oi-der of 

 the reaction according to the method of van 't PIoff. 



In the first measurement the initial pressure was 770.7 m.m. Hg. 

 After 5 minntes the CO tension amounted to 430.5 m.m. Hg from 

 which 



dc. 



— = 08,04 

 dt 



and for the average pressure of the carbonic oxide 



Cj r= 600,6 



In the second measurement the initial pressure was 442.2 m.m. Hg 

 and after 5 minntes the CO pressure amounted to 239.0 m.m. H«r. 



Here '-^ = 40,64 and c, = 340,6. 



dt 2 > 



If from this we calculate ;/ according to the formula of van 'tHoff 



-^ydt dt) 



n = , 



loci {t\ • Cj) 



we obtain 



w = 0,91. ^) 



2. After having thns become convinced that the reaction at 445° 

 is also a unimolecnlar one we made a series of measurements in 

 order to calculate the reaction constant from theui. 



The result was as follows: 



1) The quantity pf iron present in pumice did not appear to exert any influence 

 as no alteration in pressure was noticed in a reaction ve.«sel containing pumice 

 and GO when heated to 4^5'^. This lime, however, as in Schenck's cxpiniments, 

 the iron was removed from the pumice by reduction wi'h hydrogen and subsequent 

 treatment with HCl and boiling in a Soxhlet apparatus. 



The Ni(N03)o originally contained much iron, but was completely freed from it 

 by leaving the solution for some time in contact with NiCO;;. 



2) Also after a longer time (10—15 minutes) n was found to be practically 1. 



