322 NITROGENOUS HiSTOGENETIC SUBSTANCES. 



and the few which are soluble in it can readily undergo a conversion 

 into a modification insoluble in that fluid ; although their physical 

 properties are essentially dependent on and modified by water, and 

 although when dried they condense water with very great rapidity 

 from the atmosphere (and are therefore highly hygroscopic), yet they 

 show little tendency to form definite hydrates, that is to say, che- 

 mical combinations with water; they are insoluble in alcohol,, ether, 

 and in all neutral menstrua; none of them are volatile: many of them 

 certainly fuse when heated, but not until decomposition has already 

 commenced ; at a higher temperature, after the loss of water, they 

 develope a large number of nitrogenous and non-nitrogenous, basic 

 and neutral products, in addition to ammonia, evolving at the same 

 time an unpleasant odour, which is usually compared to that of 

 burnt horn. 



A very large number of the substances belonging to this group 

 dissolve unchanged in acetic and other organic acids, as well as in 

 common phosphoric acid; and also partially in other mineral acids 

 in a state of extreme dilution. On the other hand, almost all of 

 them are decomposed by concentrated mineral acids; many of 

 them swell and assume a gelatinous appearance in sulphuric and 

 in hydrochloric acid ; after prolonged digestion, they form, together 

 with ammoniacal salts, brown humus-like substances, which consist 

 mainly of leucine and tyrosine, (see pp. 142-3,) and a cry stalli sable 

 stinking volatile substance, which has not yet been accurately 

 investigated. All, more especially when they are heated, assume 

 a more or less intense yellow colour when treated with concentrated 

 nitric acid. 



They are all metamorphosed by prolonged boiling with water ; 

 and the metamorphoses they thus experience from being heated 

 with water, have led to their classification into albuminous and 

 gelatigenous substances. 



The alterations experienced by these bodies from the action of 

 oxidising substances, as for instance, chromic acid or manganese 

 and sulphuric acid, have been most accurately studied during the 

 last few years by Schlieper* and Guckelberger ;t and it is worthy 

 of remark that the non-nitrogenous products of this process of 

 oxidation belong to the butyric acid group, embracing all the acids 

 from formic to caproic acid and their aldehydes ; besides these we 

 must also reckon benzoic acid and hydride of benzoyl; but except- 

 ing ammonia and hydrocyanic acid, there are only very few nitro- 



* Ann.'d. Ch. u. Pharm. Bd. 59, S. 1-32. 

 t Ibid. Bd. 64, S. 39-100. 



