1903.] Some Physical Properties of Nickel Carbonyl. 435 



temperature, so that the pressure in the tube seems to be rather more 

 than 40 atmospheres at the critical point. On cooling, the indicating 

 globule remained permanently displaced some distance up the tube, 

 showing the existence of a pressure developed by the decomposition of 

 the nickel carbonyl. On standing for some time the whole of the 

 nickel disappears, and the carbonic oxide pressure disappears. 



The pressure on cooling seemed to be about ten atmospheres, hence 

 the critical pressure would be about thirty atmospheres. Later it will 

 be shown that this is near the actual value. 



The critical constants of the compound being known, together with 

 the boiling point, it is possible to calculate a vapour-pressure curve. 

 It was, however, thought better to determine the vapour pressure at 

 a number of temperatures below the boiling point of the liquid, by 

 the static method, and from this curve by extrapolations to deduce 

 the values for higher temperatures. 



A wide barometer tube (about 0*7 cm. diameter) was carefully cleaned, 

 dried, and drawn off to a fine capillary tube at one end. The tube 

 was then placed upright in a vessel of pure dry mercury and exhausted 

 thoroughly with a Fleuss pump. A small tube full of nickel carbonyl 

 was now introduced at the bottom of the tube and the whole then 

 exhausted again, while surrounded by a freezing mixture, in order to 

 get rid of all adhering air, and finally sealed off rapidly at the fine 

 capillary. By this method of procedure only a very small amount of 

 decomposition took place during the sealing off", as indicated by the 

 very slight deposit of nickel. The pressure was then read off by 

 ■means of a kathetometer, while the tube was surrounded by a bath 

 kept at various constant temperatures. 



The results are appended below, together with those obtained by 

 Mittasch* by the dynamic method. 



Dewar and Jones. 





Mittasch.. 





- 9°C. 



94-3 mm. 



2° 



•05 C. 



133 



1 mm. 



- 7 



104-3 



7 



•5 



170 



5 



- 2 



129-1 



15 



•27 



238 



2 







144-5 



20 



• 2 



294 



3 



+ 10 



215-0 



24 



•26 



349 



7 



+ 16 



283-5 



29 



•52 



444 



2 



+ 20 



329-5 



34 



•29 



532 



6 



+ 30 



461-9 



39 



•97 



647 



2 



The values for - 9° C. and + 30° C. give the following Rankine 

 formula for the relation between the pressure p in millimetres of 

 mercury and the absolute temperature T. Log jtf = 7*355 - 1415/T. 

 At 200° C. (about the critical temperature) the pressure calculated 

 from this equation is 30*4 atmospheres. Taking the results obtained 



* Loo. cii. 



