542 Royal Society : — 



rivatives we are about bringing to a close ; but as the drawing up of 

 this account will necessarily occupy a considerable time, we have 

 thought it desirable to send a short abstract of the chief results we 

 have obtained, with the view of its appearing in the ' Proceedings ' of 

 the Society. 



M. Caillot, about fifteen years ago, obtained a peculiar acid 

 among the products of the action of dilute nitric acid on oil of tur- 

 pentine, to which he gave the name of Terephthalic acid, on account 

 of its generation from oil of turpentine and its isomerism with 

 phthalic acid. M. Caillot' s account of his new acid was so 

 brief and incomplete, that, although we recognized many points of 

 resemblance between it and the acid we had obtained from Burmese 

 naphtha, we were compelled to repeat his experiments on oil of 

 turpentine before we could fix with certainty the identity of the two 

 products. In the course of these experiments, in which that 

 identity was fully established, we noticed some interesting features 

 in the compounds of the acid and the derivatives we discovered ; 

 more especially the relation of terephthalic acid to the well-known 

 aromatic series, — a relation precisely analogous to that which suc- 

 cinic acid bears to the fatty acids. The close relation which exists 

 between terephthalic acid and benzoic acid is most strikingly mani- 

 fested in the great number of derivatives which are obtained from 

 the former ; indeed, nearly all of the most characteristic benzoyl- 

 compounds have their analogues amongst the derivatives of tere- 

 phthalic acid. Terephthalic acid being a bibasic acid, maintains its 

 character throughout its various transformations, and it is this fact 

 which claims particular interest. 



Terephthalic acid, as well as its derivatives, forms the first term of 

 a new series of well-characterized bodies, and may, as such, be con- 

 sidered the prototype of a great number of compounds still unknown. 



Without dwelling at present on the tedious process by which 

 terephthalic acid is produced, we may mention that it is obtainable 

 from various sources. We have, for instance, found that it is in- 

 variably formed, in a relatively small proportion, when toluylic acid 

 is prepared from cymole ; it is also formed when cymole is treated 

 with fuming nitric acid for the purpose of preparing nitrotoluylic 

 acid. It is important to mention, that whether the cymole be pre- 

 pared from oil of cumin or from camphor, the result is the same. 



Subsequently, we found that insolinic acid, which was described 

 some years ago by Hofmann as a new acid of the formula C 9 H 8 O 4 , 

 is in reality terephthalic acid. The formation of this acid from 

 oil of cumin or cuminic aldehyde by the action of chromic acid 

 on these substances, turned out to be the most ready method of 

 preparing terephthalic acid ; and the principal part of our experi- 

 ments were made with terephthalic acid which had been obtained 

 from oil of cumin by this process. 



Terephthalic acid being isomeric with phthalic acid, has the 

 formula CIPO 1 (Carbon=12, Oxygen =16), as already known. 

 When pure, it forms a white opake powder ; but if thrown down 

 from a boiling dilute alkaline solution, it may be obtained in a 



