1903.] Some Physical Properties of Nickel Carbonyl. 



429 



investigate the effect of the gaseous product of dissociation on the 

 stability of the carbonyl. 



It was found that the rate of admixture of the vapour with the 

 gases had a marked effect on the dissociation, as shown by the differ- 

 ence in the vapour densities, when taken under similar conditions, 

 in the various inert gases ; and, further, that the presence of carbon 

 monoxide produced the expected diminution in the amount of the 

 compound decomposed. In order to further confirm this, two reser- 

 voir tubes of different bore were used, one having a cross-sectional 

 area about three times that of the other (the latter will be referred 

 to as the narrow tube). In the latter, admixture could take place 

 much less readily than in the former ; consequently the surrounding 

 gas would be expected to have a smaller effect on the extent of the 

 dissociation. This was also confirmed by the experimental results ; 

 the vapour density in the narrow tube is almost independent of the 

 gas employed. 



The effect of the nature of the surface on the extent of dissociation 

 was tested by using the tubes coated internally with a film of metallic 

 nickel deposited from the vapour of nickel carbonyl by heating. The 

 film of nickel seemed to bring about a state of equilibrium more 

 rapidly, so that the vapour densities determined in these tubes were 

 lower than those in the same tubes not covered by nickel (a similar 

 effect was observed by Mittasch). 



It was found that the rate at which the liquid evaporated, as would 

 be expected in the case of a substance which readily dissociates, had 

 some effect on the extent of the dissociation. Hence, it was necessary, 

 in order to get comparable results, to arrange that approximately the 

 same tirue was taken for vaporisation in all the experiments made 

 at the same temperature. A definite encl-point could be observed in 

 each case at which the gas displaced by the vapour ceased to come 

 off, and a much slower evolution of gas took place. The experiment 

 was stopped when the more rapid evolution of gas gave place to the 

 slower. 



The results obtained are appended in the following table (Table I). 

 In the fourth column the percentages of nickel-carbonyl molecules 



dissociated are given, calculated from the formula P = ^ QT P x 100, 



where 85 is the theoretical vapour density of nickel carbonyl and 

 D is the observed value. 



Unless otherwise stated, it is to be understood that the deter- 

 mination was made in a Victor Meyer's apparatus of the usual type, 

 occasionally referred to as the wide tube. 



From the figures in the above table, it is seen that the value of 

 the vapour density, deduced from the experiments in the wide tube, 

 is greater in ethylene than in nitrogen and hydrogen. It was also 



vol. lxxi. 2 I 



