348 PROCEEDINGS OF THE AMERICAN ACADEMY 



XVIII. 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 



HARVARD COLLEGE. 



ON BENZOLTRISULPHONIC ACID. 

 By C. Loring Jackson and John F. Wing. 



Presented March 9, 1887. 



The benzoltrisulphonic acid has been prepared up to this time only 

 by Senhofer,* who made it by heating a mixture of benzol, fuming 

 sulphuric acid, and phosphoric pentoxide to 280°-290° in a sealed 

 tube, and studied its potassium, barium, lead, and silver salts, while 

 in a subsequent paper f he made a thorough investigation of the action 

 of melted potassic hydrate upon it, — a large amount of work when 

 the extreme difficulty of the method of preparation is considered. 



Our attention was first drawn to this substance while we were try- 

 ing to make the potassic benzolparadisulphonate by the method of 

 Earth and Senhofer,^ and encountered in one preparation large well- 

 formed crystals, giving with phosphoric pentachloride a chloride 

 melting above 180°, which proved on analysis to be Senhofer's po- 

 tassic benzoltrisulphonate. As we could find no mention of the ap- 

 pearance of the trisulphonate under these conditions in the papers of 

 Barth and Senhofer,t Koerner and Monselise,§ or of any other chem- 

 ists who have studied the action of sulphuric acid on benzol, we 

 searched for the cause of this abnormal result, and soon found it in 

 the fact that we had heated the crude potassic disulphonate a second 

 time with fuming sulphuric acid. After this a few experiments were 

 enough to prove that the action was due to the presence of potassic 

 sulphate, and, to our great surprise, that common sulphuric acid in 

 presence of potassic sulphate was capable of converting a beuzolsul- 

 phonic acid into the trisulphonic acid, and was as efficient in this 

 respect as the fuming sulphuric acid. 



* Ann. Chem., clxxiv. 243. t Wien. Acad. Ber., Ser. 2, Ixxviii. 677. 



I Ber. d. ch. G., 1875, p. 1478. § Gazz. Chim., 1876, p. 133. 



