LECTURE XII.] HISTORY OF CHEMISTRY. 239 



Tribasic acids are derived in the same way, from three atoms 

 of carbonic acid, by the replacement of three oxygen atoms by 

 trivalent radicals. 



Of the other highly interesting matters discussed in the 

 paper, I mention only the mode of regarding the sulpho-acids, 

 in which the analogy with the carbon acids, mentioned already, 

 again makes its appearance. Just as the latter may be derived 

 from carbonic acid, so the former may be derived from sulphuric 

 acid. We have 



2 HO(S, O 4 ) O, Sulphuric acid, 



HO (C 2 H 8 ) (S 2 O 4 ) Methylsulphonic acid, 

 HO (C 12 H 6 ) (S 2 O 4 ) O Phenylsulphonic 

 The dibasic sulpho-acids are produced from two atoms of sul- 

 phuric acid : 



ur\ in u \ /S.,O,\ M Disulphometholic acid (methylene 

 [C 2 H 2 ) ^ S - Q J O, disulphonic acid), 



wr ir T-r \ /'S-jOA n Disulphobenzolic acid (phenylene 

 tt U 



disulphonic acid). 

 Besides these, Kolbe is acquainted with intermediate acids 

 which are derived from an atom of carbonic acid and an atom 

 of sulphuric acid ; amongst them are sulphacetic and sulpho- 

 benzoic acids : 



2 HO (C,H,) ' 2 O., Sulphacetic acid, 



2 HO (C^H,) (*%?} O., Sulphobenzoic acid. 



\Oo ^4/ 



This mode of regarding them furnishes a simple explanation of 

 the conversion, observed by Buckton and Hofmann, of sulph- 

 acetic acid (really of acetonitrile) into disulphometholic acid by 

 treatment with sulphuric acid. 55 In this operation C 2 O 2 is 

 replaced by S.,O 4 . 



I cannot enter here upon the other points in this extremely 

 important paper, but must advise that a study be made of it, as 

 it is full of clever ideas. It is true that there are views advanced 

 in it with which I cannot agree. Thus, for example, Kolbe did 



53 Annalen. 100, 129. 



