( 70) 



oiilv mention it to explain wliy tlie vnlnes fur /• in onr last table 

 have not been coi'i'eclod. 



3. In criticising the experiments of Schexck and Zimmer:\[ann, it 

 must first of all be observed that thev did not reduce their NiO with 

 CO bnt with H,. This is of conrse, wrong as during the reaction 

 carbon is deposited and the catalytic Ni snrface is changed. If, as in 

 onr experiments, we start with Ni on which previously a coating of 

 carbon has deposited, it is evident that a further precipitation of car- 

 bon dnring the experiment \\\]\ be of less consequence. 



In onr former communication il has moreover been shown that 

 the activity of the catalyser tirst diminishes owing to deposition of 

 carbon, bnt finally becomes practically constant. 



If, therefore, we start with Ni without carl)on we may expect that, 

 on account of the deposition of carbon, /• will continuously decrease. 

 The vabies for /• found by Schexck and Zimmermann are not at all 

 constants and show a decrease with an increase of the time. 



To find out Avhat can be the cause of the himohcular course 

 at 445° as found by Schenck and Zimmermanx we have re])eated the 

 experiment with pumice-nickel in ^^lli(•ll the NiO had been reduced 

 with very pure hydrogen. ^) 



Our first work was again the determination of the order of the 

 reaction. 



l^t measurement. Initial pressure = 756,0 m.m. Ilg 



CO pressure after 3 min. =: 528,6 ,/ n 



^ = 75,8 c, = 642,3 



2'»'1 measurement. Initial })ressure = 275,1 m.m. Ilg 



CO pressure after 2 min. == 210,9 ,/ ,/ 



^^ = 32,1 c, z= 243,0 



therefore n = 0,9 ^). 



Having found that, contrary to the statement of Schexck and 

 ZiMMERMAXX, the reaction with this catal3'ser is also uuimoJeciiltr we 

 made a further series of measurements in order to calculate k. 



The results were as follows: 



1) By electrolysis of a NaOH solution, using nickel electrodes. 



2) After a longer lime (,"j — 10 minute?) n was found to be practically 1. 



