1903.] Some Physical Properties of Nickel Carbonyl. 437 



The latent heat of vaporisation of Ni(CO) 4 , is 38' 1 calories per 

 gramme, and the Trouton constant (molecular latent heat divided by 

 the absolute boiling point) is 206, its value for ether being 22. The 

 number obtained by dividing the absolute critical temperature by the 

 critical pressure, which is proportional to the volume of the molecule,. 

 Van der Waal's constant b, is 15 5 ; the similar number for carbon 

 monoxide is 3*7, so that nickel carbonyl according to theory has a 

 molecule 4*2 times larger than carbon monoxide. The molecular 

 volume of nickel carbonyl at its boiling point is 136, as compared 

 with 110 for ether. The critical density appears to be about 0*46, 

 while that of ether is only 0-25. If the liquid densities of Mond and 

 Nasini* are taken with the critical data, then the Waters ton formula 

 v = 2-0398 - 0-5667 log (198-7 - t) fits in very well with the results. 

 A similar formula for ether given by Avenarius is : — 



v = 3-19-0-802 log (191 -t). 



The molecular volume of nickel carbonyl at its boiling point is 136, 

 subtracting from this 7 - 2 for the nickel atom, we have 32 -2 as the 

 volume of each molecule of carbon monoxide in the molecule. Now 

 liquid carbon monoxide at its boiling point has the molecular volume 

 of 35, so that contraction would take place if liquid carbon monoxide 

 could combine with nickel. The heat of formation of nickel carbonyl 

 is about four times greater than that of the liquefaction of the equi- 

 valent amount of carbonic oxide under normal conditions. 



The experiments described above show clearly that nickel carbonyl 

 is a substance admirably suited for the demonstration of the 

 phenomena of dissociation. Great care must, however, be taken in 

 handling the substance, owing to its poisonous properties when inhaled. 

 It also forms an excellent illustration of a reversible reaction, and the 

 following experiments serve to illustrate the way in which it may be 

 used for this purpose. 



A number of carefully dried tubes were exhausted by means of a 

 Fleuss pump, and were then filled with a mixture of 10 per cent, 

 nickel carbonyl vapour and 90 per cent, carbon monoxide, at pressures 

 of 50, 100, 226, 304, 396, 504, and 624 mm. of mercury respectively. 

 These tubes were then heated in a bath until nickel began to deposit ; 

 the tube under observation was then kept at that or a slightly higher 

 temperature for about half-an-hour, and afterwards tested for the 

 presence of nickel carbonyl by heating a clean portion of the tube with 

 a fine pointed flame, and in this way the presence of even a very small 

 trace of nickel carbonyl was immediately detected by the formation of 

 a bright mirror of nickel on the hot part of the tube. The tube at 

 50 mm. pressure did not deposit nickel when placed in alcohol vapour, 



* Loc. cif. 



