Chemical Analysis of Tabasheer. 133 



Smithson, and renders the accuracy of the statement of the 

 great quantity of potash, announced by Fourcroy and Vau- 

 quelin, rather doubtful. 



1. The tabasheer which I examined, was a very beautiful 

 looking substance, in small irregular fragments of a blueish 

 white colour and pearly lustre, not unlike chalcedony in 

 appearance, but much softer. For it was incapable of 

 scratching calcareous spar, and only slightly scratched sul- 

 phate of lime. When put into water, it gives out a great 

 deal of air with a kind of crackling noise, and imbibes a 

 great deal of water. 



I found its specific gravity, (taken without allowing time 

 for the internal air to escape), 1-9238. But, when by means 

 of heat all the air bubbles had been driven off, the specific 

 gravity was as high as 2-0824. 



2. When ignited, it lost 4-87 per cent, of its weight. 

 This loss consisted chiefly of water ; but not entirely, 

 for the tabasheer exhaled a peculiar odour, and, shewed 

 evidently, the existence of a small quantity of vegetable 

 matter in it. 



3. Ten grains of tabasheer reduced to a fine powder were 

 digested in distilled water for 24 hours. The water when 

 concentrated was tasteless; but slightly reddened vege- 

 table blues. Being evaporated to dryness, grayish scales 

 remained, weighing 0-6 gr. These scales being digested 

 in muriatic acid, a little iron was dissolved, but the scales 

 consisted almost entirely of silica. Thus, it appears, that 

 the silica in the tabasheer is still soluble in water. I am 

 disposed to consider, the reddening of vegetable blues in 

 this case, as produced by the dissolved silica ; at least, I 

 did not succeed in finding any trace of any other acid sub- 

 stance. When the muriatic acid dissolved upon the scales 

 was evaporated to dryness, a brown matter remained, which 

 besides iron, contained also a trace of vegetable matter; 

 but too small to admit of examination. It contained also a 

 little lime and a little silica. 



4. Ten grains of tabasheer reduced to a fine powder, were 

 mixed with 24 grains of finely pounded fluor spar, and the 

 whole was made into a thin magma by means of sulphuric 

 acid. This mixture was exposed for some hours to the 

 heat of the sand bath in a platinum crucihle. After the 

 fxhalations ol liuosilicic acid had ceased, the crucible was 



