1903.] Some Physical Properties of Nickel Carbonyl. 



431 



noticed that the deposit of nickel in the latter two gases extended 

 higher up the tube than in the former, and was higher in hydrogen 

 than in nitrogen. In carbon monoxide, on the other hand, the vapour 

 density is higher than in the gases hydrogen, nitrogen, or ethylene, 

 the values at 100° C. being nearly normal, and the dissociation was 

 incomplete even in aniline vapour. This demonstrates very clearly 

 the effect of the presence of one of the dissociation products on the 

 amount of the dissociation. 



In the narrow tube, however, the values obtained at 100° C. do not 

 seem to depend, to any great extent, on the nature of the surrounding 

 gas, the values in carbon monoxide and in the inert gases being almost 

 identical, which shows the great effect of rate of admixture and 

 diffusion on the dissociation. 



The amount of dissociation increases rapidly with the temperature ; 

 in nitrogen at 155° C. it is practically complete. The rate of increase 

 in carbon monoxide is distinctly slower, the difference between the 

 vapour densities in nitrogen and carbon monoxide at 129° C. being 

 quite marked. Above 155° C. the results obtained are somewhat 

 irregular j but dissociation seems to be nearly complete at atmospheric 

 pressure, since only a small deposit of nickel could be obtained when 

 the tube was placed horizontally and a clear part heated with the 

 blowpipe. 



A few vapour-density determinations were also made by Hoffmann's 

 method at temperatures between 17° C. and the boiling point of aniline 

 (182° C.) in order to observe the dissociation of the undiluted vapour. 

 Complete dissociation is practically reached at 182° C, but even then 

 the application of a pointed flame to a clear portion of the tube 

 produced a slight deposit of nickel, so that traces of nickel carbonyl 

 were still present. 



The results are given in the appended table (Table II). 



The results of the experiments in the narrow tube are given in the 

 fifth column for the sake of comparison, the phenomena in this case 

 being practically the dissociation of the vapour in contact with its own 

 dissociation products. The dissociation is clearly greater under 

 reduced pressure, as might be anticipated. 



The general results of the vapour-density determinations are readily 

 seen from the curves in fig. 1 (p. 433). 



Having thus found that the vapour of nickel carbonyl was much 

 more stable at elevated temperatures than had hitherto been suspected, 

 we resolved to examine the stability of the liquid under pressure, and 

 if possible make observations on it as far as its critical point. 



Small sealed tubes, from one-half to one-third full of nickel carbonyl, 

 were heated to 200° C. without bursting. A small quantity of nickel 

 was deposited on the first heating, and it was found that its quantity 

 was not appreciably increased on repeating the operation. On 



2 I 2 



