868 PRINCIPLES OP CHEMISTRY 



as determined by the vapour density and depression of the freezing 

 point. Cobalt and many other metals do not form volatile compounds 

 under these conditions, but ir&n gives a similar product (Note 26 bis). 

 Ni(CO) 4 is prepared by taking finely divided NL(obtained by reducing 

 NiO by heating it in a stream of hydrogen, or by igniting the oxalate 

 NiC 2 O 4 ) 39 and passing (at a temperature below 50, for even at 60 

 decomposition may take place and an explosion) a stream of CO over 

 it j the latter carries over the vapour of the compound, which condenses 

 (in a well-cooled receiver) into a perfectly colourless extremely mobile 

 liquid, boiling without decomposition at 43, and crystallising in needles 

 at 25 (Mond and Nasini, 1891). Liquid Ni(CO) 4 has a sp. gr. 1-356 

 at 0, is insoluble in water, dissolves in alcohol and benzene, and burns 

 with a very smoky flame due to the liberation of Ni. The vapour when 

 passed through a tube heated to 180 and above deposits -a brilliant 

 coating of metal, and disengages CO. If the tube be strongly heated 

 the decomposition is accompanied by an explosion. If Ni(CO) 4 as 

 vapour be passed through a solution of CuCl 2 , it reduces the latter to 

 metal ; it has the same action upon an ammoniacal solution of AgCl, strong 

 nitric acid oxidises Ni(CO) 4 , dilute solutions of acids have no action ; 

 if the vapour be passed through strong sulphuric acid, CO is liberated, 

 chlorine gives NiCl and COCl a ; no simple reactions of double decom- 

 position are yet known for Ni(CO) 4 , however, so that its connection 

 with other carbon compounds is not clear. Probably the formation of 

 this compound could be applied for extracting nickel from it ores. 40 



PtCl 2 (CO)3 (Chapter XXIII., Note 11), offers the greatest analogy to Ni(CO) 4 . This 

 compound' was obtained as a volatile substance by Schutzenberger by moderately 

 heating (to 285) metallic platinum in a mixture of chlorine and carbonic oxide. If we 

 designate CO by Y, and an atom of chlorine by X, then taking into account that, 

 according to the periodic system, Ni is an analogue of Pt, a certain degree of corre- 

 spondence is seen in the composition NiY 4 and PtX 8 Y 2 . It would be interesting to 

 compare the reactions of the two compounds. 



59 According to its empirical formula oxalate of nickel also contains nickel and 

 carbonic oxide. 



40 The following are the thermo-chemical data (according to Thomson, and referred 

 to gram weights expressed by the formula, in large calories or thousand units of heat) 

 for the formation of corresponding compounds of Mn, Fe, Co, Ni, and Cu (-* Aq signifies 

 that the reaction proceeds in an excess of water) : 



R=Mn Fe Co Ni Cu 



128 100 95 94 63 



106 78 73 72 41 



76 48 43 41 82 



95 68 63 61 88 



193 169 163 163 130 



4-16 18 18 19 11 



These examples show that for analogous reactions the amount of heat evolved in 

 passing from Mn to Fe, Co, Ni, and Cu varies in regular sequences as the atomic weight 

 increases. A similar difference is to be found in other groups and series, and proves 

 that thermo-chemlcal phenomena are subject to the periodic law- 



