WEITINGS OF JAMES SMITHSON. 15 



2. The nature of this substance is very different from 

 what might have been expected in the product of a vegeta- 

 ble. Its indestructibility by fire; its total resistance to 

 acids ; its uniting by fusion with alkalies in certain propor- 

 tions into a white opaque mass, in others into a transparent 

 permanent glass ; and its being again separable from these 

 compounds, entirely unchanged by acids, &c., seem to afford 

 the strongest reasons to consider it as perfectly identical 

 with common siliceous earth. 



Yet from pure quartz it may be thought to differ in some 

 material particulars ; such as in its fusing with calcareous 

 earth, in some of its effects with liquid alkalies, in its taste, 

 and its specific gravity. 



But its taste may arise merely from its divided state, for 

 chalk and powdery magnesia both have tastes, and tastes 

 which are very similar to that of pure Tabasheer ; but when 

 these earths are taken in the denser state of crystals, they 

 are found to be quite insipid; so Tabasheer, when made 

 more solid by exposure to a pretty strong heat, is no longer 

 perceived, when chewed, to act upon the palate, § IV. (A). 



And, on accurate comparison, its effects with liquid alka- 

 lies have not appeared peculiar; for though it was found on 

 trial,^that the powder of common flints, when boiled in some 

 of the same liquid caustic alkali employed at § IX. (A) was 

 scarcely at all acted upon ; and that the very little which 

 was dissolved, was soon precipitated again, in the form of 

 mmute Jlocculi, on exposing the solution to the air, and was 

 immediately thrown down on the admixture of an acid; yet 

 the precipitate obtained from liquor silicum by marine acid 

 was discovered, even when dry to dissolve readily in this 

 alkali, but while still moist to do so very copiously, even 

 without the assistance of heat; and some of this solution, 

 thus saturated with siliceous matter by ebullition, being ex- 

 posed to the air in a shallow glass, became a jelly by the 

 next day, and the day after dried, and cracked, &c., exactly 

 like the mixtures § IX. (D and E). And another portion of 

 this solution mixed with marine acid afforded no precipi- 



