Prof. Miller on Tourmaline, Dioptase, and Anatase. 277 



From the above results, and from a few doubtful experiments 

 which have not been mentioned, I conclude that compounds 

 of nitrogen with boron and silicon had been formed, and that 

 their chemical relations are similar to those of cyanogen; 

 and I have no doubt that analogous compounds of alumi- 

 nium, glucinium, &c. may also be formed ; moreover, I have 

 hopes that the fundamental principles of the science of che- 

 mistry may be further elucidated by some of these compounds 

 proving to be, if not some of our " elements," at least of a 

 nature closely analogous. We are not to suppose that the 

 affinity of nitrogen for the other elements is weak because it 

 will not unite with them directly as by a process of combus- 

 tion, especially as the compounds of nitrogen at present known 

 are not formed directly, and in many the affinity has proved 

 stronger than was at first supposed. This compound of boron 

 and nitrogen resists all agents but oxygen, and analogous 

 compounds with bases not so easily oxidized might appear to 

 us elementary, and a glance over the relative constitution of 

 our earth and atmosphere may in some measure justify us in 

 expecting to find nitrogen abundantly in the mineral king- 

 dom; and this point decided positively, may throw much light 

 upon the connexion between organic and inorganic chemistry. 

 My opinion is founded upon a careful review of many well- 

 known facts, and is not solely dependent upon these recent 

 experiments for its support, but, on the contrary, they have 

 been instituted to discover evidence, and I hope that while 

 my labours are still continued others will be induced to join 

 in the same pursuit. 



William H. Balmain. 



XL VI I. On the Optical Constants of Tourmaline, Dioptase 

 and Anatase. By W. H. Miller, M.A., F.R.S., Professor 



of Mineralogy in the University of Cambridge* . 



r |^HE values of the optical constants of Tourmaline were 

 deduced from observations made with a prism cut out of 

 a colourless crystal in the possession of Mr. Brooke, which, 

 though not sufficiently perfect to show the dark lines in the 

 spectrum, exhibits the bright line in the flame of alcohol very 

 distinctly. For this light the index of refraction of the ordi- 

 nary ray out of air into the crystal is 1*6366; in an extraor- 

 dinary ray perpendicular to the axis of the rhombohedron the 

 velocity of light in air divided by its velocity within the cry- 

 stal is T6193. A slice of the same crystal bounded by planes 

 perpendicular to the axis, 0*68 inch thick, being placed in a po- 

 * Communicated by the Author. 



