186 CONJUGATED ACIDS. 



of different nitrogenous substances by nitric acid. The other acids 

 of this class, to which reference may be made in zoo-chemistry, 

 will be considered under the head of the substances from which 

 they are derived. 



There are but few of the pure organic acids whose adjunct can be 

 determined with much probability. It necessarily arises from the 

 nature of these substances, that conjugated organic acids can be de- 

 composed into acids and their adjuncts with much less facility than 

 the conjugated mineral acids, and that their proximate constituents 

 cannot be ascertained without difficulty. We have ventured in the 

 following pages to enumerate nitrogenous organic acids in the group 

 of conjugated acids, not that the composition of each one can with 

 certainty be referred to a nitrogenous adjunct and an acid, but 

 because the study of the products of decomposition of such bodies 

 renders it tolerably evident that all nitrogenous acids, more especially 

 on account of their high atomic weight, are composed of proximate 

 constituents, of which the nitrogenous one scarcely at all contri- 

 butes to the acidity of the combination. 



This, however, is pure conjecture ; but, at the same time, in 

 considering the nitrogenous acids, we should have to adopt an arbi- 

 trary classification, if we were to consider those in which the con- 

 jugate constitution has to any extent been proved, distinct from 

 those in which no evidence of this nature has been obtained. 

 Between these two classes there exist so many analogies that it 

 would be of no practical utility to attempt such a separation. 



PICRIC ACID. C 12 H 2 N 3 O 13 .HO. 



Properties. This acid, which was formerly known as carbo- 

 nitric acid, carbazotic acid, and Welter's bitter, crystallises in 

 yellow, glistening plates or prisms, fuses when carefully heated, 

 and admits of being sublimed undecomposed, but when rapidly 

 heated decomposes with explosions ; it is devoid of odour, has a 

 very bitter taste, and dissolves slightly in cold and readily in hot 

 water, the solution being of a yellow colour ; it dissolves freely in 

 alcohol and ether, and reddens litmus ; when heated with phos- 

 phorus or potassium it decrepitates violently ; it is not decomposed 

 by chlorine, nitric or hydrochloric acids, or by aqua regia. 



Composition. According to the above formula this acid con- 

 sists of: 



