OF ARTS AND SCIENCES. 201 



I. 0.2065 grm. of the acid dried at 100° gave 0.1652 grm. AgBr. 

 II. 0.2648 grm. of the acid dried at 100° gave 14.2 c.c. of moist nitro- 

 gen at 20° and under a pressure of 763 mm. 



Found. 

 I. II. 



34.04 



6.15 



This acid will be further studied in this Laboratory. There can be 

 no doubt, however, that, like the nitropyromucic acid of Kliukhardt, it 

 contains the nitro-group in the S position. 



/3y-DlBROM-$-SrjLPHOPYROMUCIC ACID. 



/3y-dibrompyromucic acid dissolves in fuming sulphuric acid without 

 the slightest carbonization, and is converted in a short time into the 

 corresponding sulphonic acid. A large part of our work was done with 

 material made from pure /3y-dibrompyromucic acid. We subsequently 

 found, however, as will be described more at length later in this paper, 

 that the /3S-dibrotnpyrornucic was but little affected by fuming sulphuric 

 acid if the action were not too long continued, and that the mixture of 

 the isomeric dibrompyromucic acids obtained from pyromucic tetrabro- 

 mide could therefore advantageously be employed direct. The mixed 

 acids were dissolved in once and a half their weight of fuming sulphuric 

 acid, and the solution diluted with water after the lapse of two or three 

 hours. The /3S-dibrompyromucic acid thus precipitated was removed 

 by filtration, and the solution neutralized as usual by baric carbonate. 

 The small amount of /3S-dibrompyromucic acid, or its decomposition 

 products, which remained in solution, could readily be removed by the 

 recrystallization of the barium salt which was obtained after evapo- 

 ration. Since the separation of the isomeric dibrompyromucic acids 

 is a matter of some difficulty, the preparation of the sulphonic acid 

 in question is thus greatly facilitated. The free acid is very soluble 

 even in cold water, but is more sparingly soluble in ordinary concen- 

 trated sulphuric acid. From sulphuric acid it crystallizes in clustered 

 needles, from water it is deposited in broad flat prisms, which are per- 

 manent under ordinary atmospheric conditions. 



Baric (Sy-Dibrom-h-Sulphopyromncate, BaC 5 Br 2 SO c . 5 H 2 0. — This 

 6alt is very readily soluble in hot water, more sparingly in cold water. 

 The hot saturated solution solidifies on cooling, with the separation of 

 long silky radiating needles. The air-dried salt contains five molecules 

 of water, a part of which it loses over sulphuric acid. 



