OF ARTS AND SCIENCES. 455 



with a small optical angle and strong negative double refraction like 

 the other vcrmiculites and magnesian micas. The hardness of the 

 mineral is about 1.5 ; two determinations of its specific gravity (taken 

 in alcohol at 22° C.) gave 2.160 and 2.161. Heated in a closed tube, 

 it gives off water acid in reaction, changes color, and doubles its vol- 

 ume, and in the forceps before the blowpipe fuses to a dirty enamel. 

 The mineral, dried at 100°, lost upon ignition 



(1.) (2.) (3.) (4.) (Mean.) 



11.21 11.50 11.13 11.43 11.32 



per cent of its weight. The details of these determinations will be 

 referred to hereafter. 



In (1), (2), (3), and (4) of the following analyses, the ignited min- 

 eral was decomposed by fusion with sodic carbonate ; in (5) and (6), 

 the mineral, dried at 100°, was decomposed by hydrochloric acid. In 

 all, the ferric and aluminic oxides were weighed together, and the for- 

 mer subsequently determined by reduction and titration with a solution 

 of potassic bichromate. In (4), the iron and alumina were together 

 separated from magnesia by precipitation by ammonia, with the usual 

 precautions. In (5), the bases were converted into nitrates, and alu- 

 mina and iron separated from magnesia by Deville's process. In both 

 (4) and (5), the magnesia was weighed as the pyrophosphate. A 

 trace only of ferrous iron was found. The spectroscope indicated 

 small amounts of lithium and potassium.* 



100.20 100.14 100.46 100.17 



Analysis (5), which probably represents the amount of magnesia 

 contained in the mineral more correctly than (4), affords the ratio, 



* In Hallite and Jefferisite, as well as in the Lerni and Pelham varieties, small 

 amounts of lithium were detected. In none of the vermiculites have we been 

 able to detect fluorine. 



