59 



the longer it is subject to the pressure, the more slowly it appears to be 

 evolved when the pressure is removed. 



The gummy silica which adhered to the white crust was removed 

 as carefully as possible while the crust was still moist ; the latter was 

 then placed upon dry filtering paper, which was frequently renewed, so 

 as to imbibe all the moisture. A portion was broken into small frag- 

 ments, and laid upon dry filtering paper under a bell-glass along with 

 a sulphuric acid desiccating dish filled with water. The air being always 

 saturated with moisture, the carbonate of potash in the substance deli- 

 quesced, and was absorbed by the filtering paper. The operation was 

 repeated until dry paper was no longer wetted by the crust. So com- 

 pletely was the carbonate of potash removed by this process, that even 

 after an exposure of several months to the air under a large bell- glass, 

 which was frequently lifted in order to allow the substance to be moved 

 about on the paper, it only yielded a few minute bubbles of carbonic 

 acid when treated with acid. 



Thus dried it formed small porous lumps, which crushed between 

 the fingers into a snow-white gritty crystalline powder, formed of ex- 

 tremely fine oblique prismatic needles. Heated in a crucible to a red 

 heat, it lost water ; heated in the blowpipe flame, it fused into a milky- 

 looking glass, which under a very strong heat became transparent. 

 Thus fased, it was scarcely acted upon by boiling oil of vitriol, even 

 though boiled with it for some hours. In the hydrated state, it was 

 decomposed by boiling concentrated hydrochloric acid, but only very 

 slowly ; it was readily attacked by oil of vitriol. Por the purposes of 

 analysis a small quantity of the powder, produced by crushing the lumps 

 between paper, was shaken up with distilled water for some minutes, 

 in order to remove as far as possible all traces of carbonate of potash, 

 placed upon filtering paper, and repeatedly pressed, and then dried at a 

 temperature of about 60^ cent, in a current of air. The substance was 

 decomposed by concentrated hydrochloric acid, and the silica and potash 

 directly determined, the latter being weighed as chloride. The results 

 of the analysis led to the formula X0,5Si02,14H0, as the following 

 table shows: — 



Calculated. Found. 

 KO, .... 14-381 .... 14-410 

 SiOa, .... 47-227 .... 47'232 

 HO, ... . 38-391 .... 38-433 



100-000 100-075 



A portion of the unbroken crust under which the filtering paper was 

 changed only a few times, was left to dry gradually. As it did so, some 

 carbonate of potash effloresced on it ; this was derived from the mother- 

 liquor, and not from the decomposition of the compound, as a portion of 

 the latter left to dry for several months, and then well washed, had the 

 same composition as that above given. During the drying the crust 

 exfoliated into thin layers, which were often perfect shells wherever 



