194 MR JAMES DEWAR ON THE OXIDATION PRODUCTS OF PICOLINE. 



salt of this mixture gave, on the addition of nitrate of silver, a gelatinous preci- 

 pitate agreeing in appearance and composition with that got from dicarbopyri- 

 denic acid ; it contained 56 6 per cent, of silver. The equivalent of this mix- 

 ture, as determined by the composition of the ammonium salt dried at 100° C, 

 was 336 ; 0*8335 grm. of acid mixture dried at 100° C, and treated with 

 ammonia, increased in weight by 0*0422 grm. This acid substance, therefore, 

 was clearly a mixture of dicarbopyridenic acid with some acid of a very much 

 higher atomic weight. It remained solid when heated to 220° C, at which 

 temperature dicarbopyridenic acid readily melted, and was much less soluble 

 in water than the latter. 



The difficulty and expense of obtaining these oxidation products in any 

 quantity, prevented me from making the exhaustive investigation I would have 

 liked. 



The formation of dicarbopyridenic acid by the oxidation of a mixture of 

 picoline and lutidine, whether obtained from lutidine alone or by the complete 

 destruction of picoline, is quite analogous to the formation of phthalic or teraph- 

 thalic acid, by the oxidation of the homologues of benzol, or by the complete 

 destruction of benzol itself, as shown by Carius ; the only difference being that 

 Carius employed the lowest member of the benzol series, whereas picoline is the 

 second known member of the basic series. The production of the same acid from 

 pyridine itself would in no wise influence speculation regarding the constitution 

 of the higher members of the series. For the present, we may consider pyridine 

 as the nucleus from which all the other members of the series are derived. 

 Although such a supposition must be considered purely hypothetical, in reality 

 it is a great advantage to classify by analogy, relatively to other series, disjointed 

 groups of organic compounds. The two series of bases, viz., the coal-tar and 

 the chinchonine, bear the same empirical relation to pyridine that benzol does 

 to its homologues and to naphthaline. 



Benzol. 



Toluol. 



Naphthaline. 



C 6 H 6 



C 6 H 6 



CH 2 



C 6 H 6 



C 4 H 2 



Pyridine. 



Picoline. 



Chinoline. 



C 5 H 5 N 



C 5 H 5 N 



C 5 H 5 N 





C H 2 



C 4 H 2 



Now, although it has not yet been proven that lutidine and chinoline have a 

 similar formative relation to pyridine that tolnol and naphthaline have to 

 benzol, still it is by no means an improbable analogy. The isomerism in the 

 pyridine series, so far as is known, commences with the third member, lutidine, 

 as found by Williams on comparing the chinchonine lutidine with the coal-tar 

 lutidine ; whereas the chinoline obtained from either source differs essentially 

 in chemical characters. If we consider picoline as in all likelihood methyl- 



