1892.] on Metallic Carhonyls. 669 



ready to attack with its two free valencies anytliing coming in its 

 way, until very recently we only knew it to interact and to combine 

 with substances possessing themselves extreme attacking powers, such 

 as chlorine and potassium. Although Liebig had so long ago pro- 

 claimed it as a radical, the chemical world was startled when, two 

 years ago, I announced in a paper I communicated to the Chemical 

 Society in conjunction with Drs. Langer and Quincke, that carbonic 

 oxide combines at ordinary temperature with so inactive an element 

 as nickel, and forms a well-defined compound of very peculiar 

 properties. 



The fact that carbonic oxide does not possess the chemical 

 activity one would suppose in a radical composed of single atoms 

 may, I believe, be explained by assuming that the two valencies of 

 carbon which are not combined with oxygen do satiate or neutralise 

 each other. Everybody admits that the valencies of two different 

 carbon atoms, which are all considered of equal value, can neutralise 

 each other. I see, therefore, no reason to question the possibility of 

 two valencies of the same carbon atom neutralising each other. On 

 this assumption carbonic oxide may be looked upon as a self satisfied 

 body — one which keeps in check its free affinities within itself. I 

 have tried to explain this by the graphic formula in this diagram. 



You have here (see diagram on next page) the typical carbon 

 radicals containing one atom of that element, acetylene, methylene, 

 methyl, cyanogen, and carbonyl. In the second column you have 

 these substances as they are known to us in the free state. You see 

 the carbonyl is the only one which exists in the free state as a single 

 atom, while all the others only exist as molecules, composed of two 

 atoms the free valencies of which neutralise each other. The carbonyl 

 I have represented in the last formula, with the two valencies not 

 combined with oxygen neutralising each other, so that in this way it 

 also becomes a satiated body. 



The paper published by Liebig in 1834, from which I have 

 already quoted, was entitled " On the Action of Carbonic Oxide on 

 Potassium." In it Liebig fully described the preparation and pro- 

 perties of the first metallic carbonyl known — a compound of potassium 

 and^ carbonic oxide. Liebig obtained this compound by the direct 

 action of carbonic oxide upon potassium at a temperature of 80° C, and 

 proved it to be identical with a substance which had been previously 

 obtained as a very disagreeable bye-product of the manufacture of 

 potassium from potash and carbon by Brunner's method. It forms 

 a grey powder which is not volatile, and which on treatment with 

 water yields a red solution, gradually turning yellow in contact with 

 air and from which on evaporation a yellow salt is obtained called 

 potassium croconate, on account of its colour. Liebig showed this 



