354 PROCEEDINGS OF THE AMERICAN ACADEMY 



acid by boiling them together in a flask with a reverse cooler;* when 

 the solution is complete, the product is mixed with its own volume of 

 common sulphuric acid and between 60 and 70 grams of potassic sul- 

 phate, and distilled in an untubulated retort till about one third of the 

 total amount of sulphuric acid used has passed over. The liquid boils 

 quietly without bumping. The residue is then divided into two parts, 

 and these are heated in porcelain dishes precisely as in the previous 

 process. The product is much more impure than when made from the 

 potassic disulphonate, and it is better therefore to decolorize it by treat- 

 ment with plumbic oxide after a part, but not the whole, of the large 

 excess of sulphuric acid has been removed by marble or baric carbon- 

 ate, since the greater part of the coloring matter is precipitated on 

 adding an excess of plumbic oxide if the solution is acid, and still more 

 comes down with the plumbic carbonate when potassic carbonate is 

 added to the filtrate ; but if the solution is thoroughly neutralized by 

 the marble, very little, if any, of the colored impurity comes down 

 with the lead salts, and in that case it is very hard to get rid of it. 

 The yield was very small, and, although we could have raised it un- 

 doubtedly by working up the insoluble residues, we have never tried 

 to do so, because we have found it easier to prepare a fresh portion 

 than to purify the highly colored salts which would be obtained in this 

 way. It is advisable, however, to heat once more with sulphuric acid 

 the brown impure residues left by the evaporation of the mother liquors, 

 from which no more crystals of benzoltrisulphonate can be separated, 

 as in this way an additional quantity of the trisulphonate can be ob- 

 tained. We have tried also to purify the impure residues left after 

 the removal of the crystals by treatment with phosphoric pentachloride, 

 and washing the product with ether or chloroform, but have obtained 

 only unsatisfactory results. 



The secondary products formed in this process are of little or no 

 interest. They consist principally of a dark reddish brown to black 

 substance giving a potassium salt of tarry consistency more soluble 

 than the potassic benzoltrisulphonate, which it will not be easy to 

 purify. There appears also on evaporation of the mother liquors a 

 dark-colored granular potassium salt, whose viscous chloride solidifies 

 after standing for some weeks, and it is then possible to obtain much 

 benzoltrisulphochloride from it by treatment with chloroform; it is 

 probable, therefore, that it consists principally of the benzoltrisulpho- 

 nate prevented from crystallizing by the presence of the dark-colored 

 impurity just mentioned, or of some potassic benzolmetadisulphonate. 



* Michael and Adair, Ber. d. ch. G., 1877, p. 585. 



