The Rev. G. Salmon on Curves of the Third Order. 71 



— I retain this name for the present — will furnish saline compounds 

 corresponding to the methyle- and ethyle-derivatives, showing that 

 this base, hke quinine, is capable of forming two groups of salts. 



It deserves to be noticed that the diammonic nature of ethylene- 

 phenylamine is also strongly marked by its deportment under the 

 influence of heat ; for while all the monammonic basic derivatives of 

 aniline are volatile without decomposition, ethylene-phenylamine, 

 when submitted to distillation, is destroyed with reproduction of 

 aniline, like the well-established diamines belonging to this group, 

 melaniline, formyl-diphenylamine, &c. 



In describing the preparation of ethylene-phenylamine, it has been 

 mentioned that the action of bibromide of ethylene on aniline gives 

 rise at the same time to two other basic compounds. These sub- 

 stances, which are formed in smaller quantity, diifer in a very marked 

 manner from the principal product of the reactions. Their study is 

 not yet completed, but it may even now be stated that they have 

 the same composition as ethylene-phenylamine itself. One of these 

 substances, remarkable for its solubihty in spirit, is capable of bemg 

 converted into ethylene-phenylamine by a simple molecular change. 

 The relation in which these three isomeric bodies stand to each 

 other is not yet finally fixed by experiment. The idea suggests itself 

 that it may possibly be represented by the formulae — 



Soluble base Ci„ H, N. 



Ethylene-phenylamine Cg, Hjg N2. 



Insoluble base C^s H.t N3 . 



" On Curves of the Third Order." By the Rev. George Salmon, 

 of Trinity College, Dubhn. 



The author remarks that his paper was mtended as supplementary 

 to Mr Cavley's Memoir " On Curves of the Third Order" (Phdoso- 

 phical Triinsactions, 1857, p. 415). He establishes in the place of 

 Mr. Cayley's equation, p. 442, a fundamental identical equation, 

 which is as follows, viz. if substituting in the cubic U, x+\x', 

 y + \y', ^ + A~' for x, y, s, the result is 



U-|-3XS-f3\-P+,V'U'; 

 so that S and V are the polar conic and polar Une of (a;', y', c'), with 

 respect to the cubic, viz. 



and if making the same substitution in the Hessian H, the result is 

 II-|-3\S-l-3X'n-FX''H', 



80 that S and II arc the polar conic and polar line of the Hessian— 

 then the identical equation in question is 



3(SII-2:P) = II'U-IIU'. 



