192 Proceedings of the Royal Society 
we employ other operators as S(V V) S(rV), S ,cr VrV, &c. (where V 
may or may not operate on u alone), we can pass to linear partial 
differential equations of the second and higher orders. Similar 
theorems can be obtained from vector operations, as Y(<r* V). 
6. On the Oxidation Products of Picoline. By James 
Dewar, F.B.S.E., Lecturer on Chemistry, Veterinary 
College, Edinburgh. 
(Abstract.) 
The author in this paper details the results of a series of experi- 
ments, commenced three years ago, on the oxidation of the 
pyridine series of bases. These bodies are readily attacked by 
permanganate of potash ; and the oxidation products of picoline 
thus obtained are ammonia, carbonic, nitric, oxalic, acetic, and 
dicarbopyridenic acids, along with a very small quantity of some 
solid base, possibly a condensed base. 
CO H 
Dicarbopyridenic acid, C 5 H 3 N 
is bibasic, and bears the 
same relation to the nucleus pyridine that phthalic acid and its 
isomers bear to benzol. It crystallises from hot aqueous solutions 
in plates resembling naphthaline; the majority of its salts are 
soluble and crystallisable. The silver salt of the acid is very 
characteristic, being insoluble and gelatinous, not decomposed by 
boiling water, and not visibly affected by light. As this acid was 
got in only small quantity, the author had not the opportunity 
of producing its various derivatives. 
The author observes that the two well-defined series of nitrile 
bases found in coal tar, viz., the pyridine and chinoline series, 
bear the same relation to each other that the benzol series 
of hydrocarbons does to thehiaphthaline. Thus, pyridine is sup- 
posed to he the nucleus in these bodies that benzol is in the 
aromatic series. The following are some of the analogies pointed 
out in the paper : — 
Benzol. Naphthaline. Anthracine. Pyridine. Chinoline. 
c 2 h 2 c„h 4 c„h 4 c 2 h 2 c,ii,n 
c 2 h 2 c 2 h 2 c 2 h 2 nch c 2 h 2 
Gft C 2 H 2 C 6 H 4 C 2 H 2 C 2 H 2 
Chinoline and pyridine, therefore, ought to be readily obtainable 
