336 Dr Turner's Chemical Examination of Tabasheer. 



that this earth must exist in the fluids of the plant, not as an ac- 

 cidental, but as an essential ingredient. In what manner a sub- 

 stance of so insoluble a nature is taken up by the roots of the 

 plant has not yet been investigated ; but it is probable that con- 

 siderable light would be thrown on the subject by a chemical 

 examination of the soil in which the bamboo grows, and of the 

 fluids which circulate in its vessels. In attempting any ex- 

 planation on chemical principles two views may be suggested. 

 It may be supposed either that silica at the moment of being 

 set free by the decomposition of siliceous compounds, may be 

 dissolved in common spring-water ; or that siliceous earth, in 

 its ordinary state, is rendered soluble in water through the 

 medium of an alkali. It would be an. argument of consider- 

 able weight in favour of the latter view should potash always 

 be contained in tabasheer ; but, at the same time, the former 

 supposition is by no means impossible. The researches of 

 Berzelius have demonstrated, that when silica in the nascent 

 state is acted on by water, it is dissolved in considerable quan- 

 tity ; and hence it is not improbable, that when in the act of 

 separation from substances with which it was previously com- 

 bined, it may also, under favourable circumstances, be dis- 

 solved by water. 



When tabasheer is put into water, numerous small air-bub- 

 bles rapidly escape, the quantity of which is fully equal in ' 

 bulk to the specimen employed, and is even somewhat greater 

 in the finer varieties. The weight of the dry tabasheer com- 

 pared to that of the water which it is capable of absorbing is 

 as 1 to 2 in the chalky variety, 1 to 2.32 in the translucent, 

 and 1 to 2.24 in the transparent tabasheer. The specific gra- 

 vity of these different kinds, taken at the temperature of 56 

 Fahr. is shown by the following table. In finding the num- 

 bers contained in the first row, the air was displaced by soak- 

 ing the specimen for several hours in cold water ; in those of 

 the second, the air was more completely expelled by boiling 

 for a few minutes in water. 



r 



