1863.] 639 



tine much more fully. When munjistine is digested with moderately 

 strong nitric acid, as already stated, copious fumes are given off, the 

 munjistine gradually dissolving and forming a colourless solution. 

 When this is evaporated to dryness on the water-bath, a white cry- 

 stalline mass is obtained, consisting almost entirely of phthalic acid 

 contaminated with a small quantity only of oxalic acid. The oxalic 

 acid may be easily removed by washing the mass with a little cold 

 water and then pressing between folds of bibulous paper, or by 

 neutralizing the mixture of the two acids with lime and then treating 

 with boiling water, which dissolves the phthalate of lime. The acid 

 freed from oxalic acid by either of these methods presents all the 

 usual reactions of phthalic acid. One of the most convenient ways 

 of purifying it consists in subliming it repeatedly in a Mohr's appa- 

 ratus, when the anhydrous acid is obtained in beautifully white 

 iridescent four- sided prisms, frequently several inches in length. 

 3745 grm. of the crystals of the anhydride, burnt with chromate 

 of lead, gave '891 grm. carbonic acid and "095 grm. of water. 



Theory. Expt. Marignac. Laurent. 



C 16 ....96 64-86 64-89 64-88 64'70 



H 4 4 2-70 2-81 2-71 2-38 



O.....48 32-44 32-30 32-41 32-92 



From this result it is evident that the acid chiefly produced by 

 the action of nitric acid upon munjistine is phthalic acid, which, as 

 is well known, may also be procured from alizarine and purpurine. 

 This reaction, therefore, indicates a very close relationship between 

 these three substances, the only true colouring principles of madder 

 with which we are at present acquainted. 



VI. " Notes of Researches on the Poly- Ammonias. No. XXIV. 

 On Isomeric Diamines." By A.W. HOFMANN, LL.D.,F.R.S. 

 Received May 26, 1863. 



In a former paper* I have described phenylene-diamine, an aro- 

 matic diamine which is formed by the action of powerful reducing 



* Proc. Roy. Soc. vol. xi. p. 518. 



