1903.] Some Physical Properties of Nickel Carbonyl. 427 



€t Some Physical Properties of Nickel Carbonyl." By James 

 Dewar, M.A., Sc.D., DL.D., F.E.S., Jacksonian Professor in 

 .the University of Cambridge, ami Humphrey Owen Jones, 

 M.A., Fellow of Clare College, Jacksonian Demonstrator in 

 the University of Cambridge. Eeceived March 3, — Eead 

 March 26, 1903. 



The properties of nickel carbonyl have until recently been the 

 subject of but few investigations. Dr. Mond and his collaborators 

 in the discovery of this remarkable substance determined some of its 

 physical properties, including its boiling point, specific gravity, and 

 vapour density. Subsequently Dr. Mond, in association with Pro- 

 fessor Nasini, made observations on its molecular refraction and 

 thermal expansion. 



A substance of the peculiar molecular structure of nickel carbonyl 

 seemed to call for further study. The investigation described in the 

 present paper was carried out in the winter of 1901 ; the authors' in- 

 tention being to make a complete study of the stability of the com- 

 pound both in the gaseous and liquid conditions. While the work was 

 in progress a paper by Mittasch was published* containing an account 

 of an admirable and exhaustive investigation of the velocity of the 

 reaction between nickel and carbon monoxide, including the heat of 

 formation and vapour tensions of the compound, covering part of the 

 ground which we had examined. A number of interesting problems 

 •examined in the course of our inquiry however remain, which have 

 not been touched upon by previous investigators, and to some of these 

 the present paper is devoted. 



The vapour density of nickel carbonyl was determined by Mond, 

 Danger and Quincke t in air, at 50° C. by Victor Meyer's method. 

 The value obtained was 86*7, while theory requires 85. The vapour 

 density at this temperature is quite normal, and there is no evidence 

 of association even at this temperature only some 7° C. higher than 

 the boiling point of the compound. It was found that the vapour 

 exploded at 60° C. with a Hash of light, and carbon dioxide was 

 detected among the products of decomposition. Berth elott explained 

 the explosion as being due to the production of carbon dioxide by the 

 intermolecular reaction : — 



2CO = C02 + C, which was observed to take place when carbon 

 monoxide acts on nickel at 350° — 450° C. Later§ it was found 

 that the action only proceeded in this way to a small extent, when 



* ' Zeit. Phys. Cliein.,' 1902, vol. 40, p. 1. 



f ' Jour. Cliem. Soc.,' 1890, vol. 57, p. 749. 



% 1 Compt. Send.,' vol. 112, p. 1343. 



§ 1 Ann. Ohim. Phys.,' 1901 [7], vol. 22, p. 804. 



