On a new Form of the Reflective Goniometer. 281 



against the hypothesis that it is methyl pyridine. In all 

 methyl compounds with which we are acquainted, chlorine is 

 easily introduced in place of the hydrogen of the methyl 

 group ; and, also, the methyl group is usually easily oxidized 

 to a carboxyl group. This is certainly not the case with 

 picoline ; for, as Dewar has shown, it yields, when oxidized 

 with potassium permanganate, an acid which he named dicarbo- 

 pyridenic acid, in which two atoms of hydrogen are replaced 

 by carboxyl groups ; and pyridene, in fact, is easily prepared 

 from it by distilling it with lime. Wright supposes that 

 Dewar's picoline may have contained lutidine, and that the acid 

 may have resulted from the oxidation of two hypothetical 

 methyl groups in lutidine. But I have succeeded in preparing 

 dicarbopyridenic acid (a better name for which would be 

 pyridene dicarbonic acid) by a process similar to Dewar's ; and 

 I find that from 9 grms. of picoline about 5 grms. of dicarbo- 

 pyridenic acid are obtained ; and surely that is a proof that 

 all the acid is not derived from lutidine. I have already, in 

 the course of some preliminary experiments, made it probable 

 that the alcohol and aldehyde of this acid exist ; and I hope to 

 be able to transform the alcoholic into methyl groups, and so 

 produce true dimethyl pyridine. The facts elucidated are 

 these : — (1) The carbon and nitrogen are evidently not com- 

 bined in the manner in which they exist in a nitrile or in a carb- 

 amine ; otherwise caustic potash would produce the usual de- 

 composition. (2) Picoline does not contain an amido-group; 

 for not only does it refuse to yield an amido-compound with 

 an acid chloride, but also it is impossible to form a compound 

 with two alcohol radicals. (3) Picoline has the capacity of 

 uniting loosely with two atoms of a halogen, either when it is 

 free, or combined with an acid, or with an alcoholic bromide 

 or iodide. This probably shows that it is an unsaturated 

 compound. 



I propose to extend my researches on picoline with the view 



of ascertaining its real constitution. 



XXXV. On a new Form of the Reflective Goniometer. J5yW. H, 

 Miller, M.A., F.R.S., Fellow of St. Johns College, and 

 Professor of Mineralogy in the University of Cambridge *. 



AFTER the publication of a description of Mitscherlich's 

 Goniometer (Berlin. Abhandl. 1843, p. 189), and of 

 those employed by Babinet, Haidinger, v. Lang and Schrauf, 

 an account of any other modification of this instrument may 

 appear very superfluous. I believe nevertheless that it is 

 * Communicated by the Crystallometric Association. 



