178 Gerhard? s Organic Chemistry. 



Anhydrides. — Many organic acids by the action of heat, lose 

 the elements of water and are converted into substances which 

 in accordance with the theory which regarded the acids as com- 

 pounds of a dry acid with water, have been styled anhydrous 

 acids. These substances are neutral in their reaction and their 

 solutions have no action upon alkaline carbonates, but when long 

 boiled with water they take up the elements of that liquid and 

 regenerate acids. The acids thus obtained often differ in their 

 properties from the originals ; this has been particularly observed 

 of the anhydrides of camphoric and itaconic acids. — (Precis, 

 Vol e I, pp. 1 00-109.) 



The anhydrides formed by the action of heat alone, are those 

 of certain bi basic acids which lose their basic hydrogen in the 

 form of water. Some monobasic acids as the stearic and marga- 

 ric are decomposed by distillation with anhydrous phosphoric 

 acid and yield neutral fatty substances ; but in these the acid 

 loses two equivalents of hydrogen of which only one is basic ; 

 the type is hence destroyed and the acid cannot be regenerated 

 from them. 



In this class we may conveniently consider all those compounds 

 which under certain circumstances assume the elements of water 

 and form acids. Isatine when dissolved in a solution of potash, 

 in this way generates an isatate, and when this acid is set free, it 

 is decomposed by a gentle heat into isatiric acid and water. Cam- 

 phor also when heated with hydrate of potash yields campholic 

 acid which is formed by the union of the elements of water; ac- 

 cording to the general idea both camphor and isatine are anhy- 

 drous acids. 



Amides. — Few subjects have been the cause of more perplex- 

 ity to chemists that the action of ammonia with organic substan- 

 ces. M, Dumas first observed in the products of The dry distil- 

 lation of oxalate of ammonia, a white insoluble body to which 

 he gave the name of oxamide. It is derived from oxalate of 

 ammonia by the abstraction of the elements of water : C, H, 0, + 



2NH ! = C, H 4 N 2 O i +2H, O, and by the action of acids or 

 alkalies reassumes them and regenerates the oxalate and ammonia. 

 "When ammonia is added to a solution of chlorid of mercury, 

 hydrochloric acid is set free and forms salammoniac while a white 

 precipitate falls which is Hg, NH„ ; this may be received as 



HgNH,. The residue 

 3 „.«,.„,«„,„ w .^ured to be compound rad- 

 ical analogous to chlorine in its reactions, to which the name ot 

 amide or mnidngen was given, and oxamide was regarded as an 

 amide of CO, the assumed base of oxalic acid, C 2 H« N, Q f * 

 2(COfNH, ). Subsequently M. Laurent was induced to in 1 * 



NH, was 



l\H 



viewed as existing in many organic compounds sustaining 



the 



