230 Intelligence and Miscellaneous Articles. 



Weight. Increased to. Absorption. 



Macie .... 75-70 grras. 154-20 grms. 79-50 grms. water. 

 Brewster.. 6-65 .. 14-10 .. 745 



Guibourt.. 2-526 .. 5-224 .. 2-695 



If we calculate from these numbers the density of the porous 

 tabasheer, by adding the weight of the absorbed water (by which 

 the volume of the pores is determined) to the loss of weight under- 

 gone by the body in water (which gives the volume of the solid 

 matter), and then divide the sum by the weight of the dry body, 

 so as to obtain the density of the porous body in the natural state, 

 we get 0-727, 06227, 0-6520. 



But the tabasheers are heavier than water ; they sink in it imme- 

 diately, and have consequently a greater specific gravity than that 

 thus calculated. The author shows that Brewster observed this con- 

 tradiction, but without troubling himself about the cause, determined 

 the space occupied by the silica and the pores from this incorrect 

 specific gravity, so that the space occupied by the pores in propor- 

 tion to that filled by the silica was, according to him, as 2-307 : 1 ; 

 whilst, from the author's experiments upon the natural density of 

 tabasheer, it appears that this proportion is 0-0689 : 1, which agrees 

 with the behaviour of the body in water. 



Tabasheer which has been completely permeated by water and 

 become transparent, becomes perfectly opake in the air. This be- 

 haviour, which Brewster believed to occur only with this body, in- 

 duced him to set up a peculiar theory upon the small refractive 

 power of this substance, which he found to be less than that of any 

 other known body. But without taking into consideration that the 

 number 976-10, which Brewster adopted for the refractive power of 

 tabasheer, is too small, as the author calculates it at 1500-5, we must 

 also take into account the opacity which is peculiar to the molecular 

 state of this substance. 



Tabasheer is evidently a mass produced from a jelly by desicca- 

 tion. To obtain an insight into its production, the author has inves- 

 tigated the inorganic constituents of the bamboo. The small quan- 

 tity of pith which is seen when a bamboo is split longitudinally, con- 

 tains iron, potash, lime and silica. The ashes of the wood consist of — 

 Soluble salts. I Insoluble salts. 



Carbonate of potash. . 1-9872 

 Sulphate of potash . , 0-2905 

 Phosphate of potash. . 0-1593 

 Chloride of potassium. 0-0766 



Silica 0-0204 



2-5340 



Phosphate of lime. . 0-0928 

 Phosphate of iron. . 0-0130 



Silica 0-0408 



Loss 0-0371 



0-1837 



The author found that the silica occurred in different quantities 

 in different parts of the cane. I'he pith contained 0-448 per cent. 

 The inner wood held much less, and the greatest proportion occurred 

 in the external wood. Consequently, the author thinks the forma- 

 tion of tabasheer is easily explained in the following manner : at the 

 time when the straw is developed, the outer wood has no longer any 

 necessity for silica, which is carried inwards and deposited in the 

 cavity of the straw. — Journ, de Pharm. vol. xxvii. pp. 61 and 252. 



