Dr Brewster on the Natural History of Tahasheer. 285 



should be followed, which has been already recommended for 

 examining the clay portion of the iron-ores. 



The presence of sulphur in any coal, and its amount may 

 be investigated according to the same process which is resorted 

 to for determining the amount of that substance when it occurs 

 in an ironstone. 



We have now considered in detail both the processes of the 

 dry and the humid assay. But we cannot conclude without 

 again repeating that the humid assay is the only one which can 

 be relied on with safety for the accuracy of its results. The 

 mode by which this assay may be conducted, as stated on page 

 272, requires so little scientific skill, and so little nicety of ma- 

 nipulation, at the same time that it affords a very excellent 

 analysis of the mineral, that we have no hesitation in strenu- 

 ously recommending its adoption in every case where the smel- 

 ter can afford the necessary delay. It is hardly ^ necessary to 

 add, that when we reflect upon the very large proportion of 

 the charge in every smelting furnace, which is composed of 

 limestone and of coal, it is of little less importance to examine 

 the constitution of these minerals, than it is to analyze the ore 

 itself. 



Art. IX. — On the Natural History and Properties of Taha- 

 sheer, the Siliceous concretion in the Bamboo. By David 

 Brewster, LL.D., F. R. S. Lond., and Sec. R. S. Edin. 



1 HERE is certainly no substan,ce either in the vegetable or 

 the mineral world so remarkable as Tabasheer. Its locality 

 in the joints of the bamboo ; — its derivation from the juices 

 of that reed ; — its occurrence only in particular situations and 

 particular plants ; — its chemical composition ; — ^and its opti- 

 cal and physical properties, render it an object of very pecu- 

 liar interest to the botanical as well as to the natural philoso- 

 pher. 



In the Philosophical Transactions for 1819, I have given 

 an account of the optical and general physical properties of 

 tabasheer, as determined from specimens which my late and 

 respected friend Dr Kennedy procured for me from India. 

 Since that time, I have the good fortune to obtain the finest 



VOL. VIII. NO. II. APRIL 1828. ' T 



