1906.] on Studies on Charcoal and Liquid Air. 447 



object is inserted, the apparatus becomes a very sensitive calori- 

 meter. 



Much investigation is still necessary to clear up the nature of the 

 various charcoals and their properties. One chemical character they 

 possess, and that is that, ])y powerful oxidising agents like concen- 

 trated nitric acid or permanganate of potash, they seem all capable of 

 giving a greater or less yield of an acid called Mellitic Acid, 

 the graphical formula of which is represented in (Fig. 22), which 

 occurs in nature as the aluminium salt, commonly called Honey- 

 stone. This acid, we know, is a derivative of benzol, and its 

 production from charcoal suggests that the latter has a structure of 

 double benzine rings, each containing twelve atoms of carbon such as is 

 shown in (Fig. 28). This gives a fundamental molecule containing a 

 large number of latent valences available for chemical or physical 

 combination, and this structure may have something to do with the 

 general absorptive power of charcoal. 



The Professor thanked his assistants, Mr. R. N. Lennox and 

 Mr. J. W. Heath, for valuable aid in the conduct of these experiments. 





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