132 



M on M' 100 



M « M 80 



M '' d 133.35 



d " ^/ 135.45 



c " c 124 

 Plane / too round to be measured. 

 Terminal planes P are entirely oblit- 

 erated by modification d; on some cry.s- 

 tals they exist, but are not sufficiently 

 brilliant for accurate measurement. 



The form, as correctly slated by Prof. Shepard, is a right 

 rhombic prism, but it will be seen that this form as well as the 

 values of the angles, are precisely those of Brookite. The qual- 

 itative analysis of Arkansite by Mr. J. D. Whitney, recently read 

 before the Society, therefore leaves little doubt of its being this 

 mineral, hitherto so extremely rare as to have only been analyzed 

 by Prof. Rose of Berlin. 



The specific gravity of the oxide of Titanium has been shown 

 by this chemist in his elaborate paper, to vary according to cir- 

 cumstances. Of Rutile it is 4.25, of Anatase 3.85. 



Shepard's specific- gravity of Arkansite is 3.857. But this 

 gentleman has published the result of his qualitative analysis of 

 Arkansite, which he calls a Niobate of Yttria and Thorina. New 

 Thorina has a specific gravity of 9.00, being more than double 

 that of the highest oxide of Titanium. The presumption is, that 

 if Thorina formed an essential ingredient of Arkansite its specific 

 gravity would be much higher tlian 3.857. 



Mr. Whitney also states that its specific gravity, which he had 

 ascertained to be 4.085, is sufficient proof that its composition 

 could not be that of the Niobate in question. 



The Arkansite of Prof. Shepard is therefore unquestionably 

 identical with Brookite, and this country in another instance fur- 

 nishes in abundance a very interesting mineral hitherto of too 

 rare occurrence in Europe to reach the hands of the analyst. 



Dr. C. T. Jackson laid before the Society the results of 

 his observation of the comparative effects of the inhalation 

 of nitrous oxide, and the vapor of chloroform and sul- 

 phuric ether. 



