132 M. Hlasiwetz on Isopurpuric Acid. 



salts of silver, lead, mercury, and baryta, but not those of lime, 

 strontia, zinc, and copper. 



The composition of the potash salt is C'^*" H''K N^O'^; and 

 from two nitrogen determinations made by means of soda-lime, 

 it appeared that 3 equivs. of nitrogen were contained in a form 

 other than that of NO''. Cyanogen could not be detected. 



The soda salt is obtained by treating picric acid with cyanide 

 of sodium. It is more soluble than the potash salt, and is of a 

 dark green colour with metallic lustre. 



The ammonia salt, Ci''' H'' (NH^) N^ O'S forms beautiful 

 wedge-shaped crystals of a brownish-red colour and green lustre. 

 The baryta salt, formed by adding the potash salt to a solution 

 of chloride of barium, is a vermilion-red precipitate, which when 

 dried possesses a splendid light-green metallic lustre, and when 

 rubbed becomes red again. The lime salt, C'^H'^CaN'^O^^ + 3 HO, 

 formed by adding solution of chloride of calcium to a solution of 

 the ammonia salt,forms very beautiful green needles, often half an 

 inch long, and with a metallic lustre. The lead salt, when cry- 

 stallized from hot water, in which it is somewhat soluble, appears 

 under the microscope in the form of very fine reddish-brown 

 needles, possessing a green lustre. 



It was not possible to obtain the free acid. When the potash 

 salt was decomposed by means of a stronger acid, further decom- 

 position was set up. For this reason it is not possible to dye 

 with solutions of the salts, beautiful as they are ; for without 

 mordants, the colours on cloth are neither beautiful nor perma- 

 nent, and on mordanted cloths decomposition is soon induced. 



The salts of this acid are isomeric with those of purpuric acid 

 (which is also unknown in the free state) obtained from uric 

 acid ; on this account it has been named isojmrpuric acid. Like 

 purpuric acid, isopurpuric acid appears to be bibasic. The 

 salts of the two acids present great similarity, both as respects 

 colour of the solutions, solubility, and deportment when heated. 



The optical relations of the isopurpurates were examined by 

 Grailich. Isopurpurate of ammonia and murexide (which are 

 isomeric) are perfectly similar in their optical and crystallogra- 

 phical deportment. They appear to belong to the rhombic system. 



The formation of isopurpuric acid may be expressed by the 

 following equation : — 

 C>2H3(NO'*)302-f3C2NH + 3HO = C"5H5N50'HC20'»-fNH3. 



Picric acid. Hydrocyanic Isopurpiu'ic 



acid. acid. 



Free picric acid is not altered either in the cold or in the warm 

 by hydrocyanic acid ; but the reaction is immediately set up in 

 the presence of a base. 



In reference to the rational constitution of isopurpuric acid, it 



