OF ARTS AND SCIENCES. 355 



If the trisulphonic acid was made direct from the monosulphonic 

 acid, some henzolparadisulphonic acid was also formed, which made 

 the purification of the benzoUrisulphonate by crystallization more dif- 

 ficult. It was recognized by the melting point of its chloride, 13D°, 

 whereas Koerner and Monselise* give 131°, and the following analysis 

 of the chloride dried at 100°. 



0.1008 grm. of substance gave after decomposition by boiling with a 

 solution of pure sodic carbonate 0.1054 grm. of argentic chloride. 



Calculated for C,;Hj(S0..Cl)2. Found. 



Chlorine 25.82 25.86 



We are inclined to consider the melting point (139°) given by us for 

 the benzolparadisulphochloride as more accurate than that of Koerner 

 and Monselise (131^^), since their product was prepared from a mix- 

 ture of the para and meta compounds, and a small quantity of the 

 latter, melting at 63°, would have been enough to lower the melting 

 point very considerably, and its presence could not be determined by 

 analysis; the impurity in our product, on the other hand, would have 

 been benzoltrisulphochloride, and that there could have been no ap- 

 preciable amount of this substance present is shown conclusively by 

 our analysis. 



BenzoltrisuJphonic Acid and its Salts. 



We have little to add under this head to the excellent work of Sen- 

 hofer. The free acid, when heated, became charred, and gave off a 

 smell like caramel ; but the soluble part of the residue consisted of the 

 unaltered acid, as was shown by the crystalline form of its potassium 

 salt and the melting point of its chloride. The experiment gave so 

 little promise of interesting results, that it was not repeated on a larger 

 scale. The following analysis of the free acid dried at 100°, which it 

 was necessary to make in the course of our work, confirms Senhofer's 

 statement that it retains three molecules of water at that temperature. 



0.3772 grm. of the acid dried at 100° gave by the method of Carius 

 0.7004 grm. of baric sulphate. 



Calculated for CuHsfSOaHJa 3 HjO. Found. 



Sulphur 25.80 25.51 



We add also an analysis of the potassium salt, which yielded the 

 same amount of water of crystallization (three molecules) as given by 



* Gazz. Chim., 1876, p. UO. 



