In the year 1806, MM. Foureroy and Vauquelin gave an account of a specimen of tabasheer brought from South America in 1804 by Humboldt and Bonpland (Mem. de l'Inst., vol. vi., p. 382). It was procured from a species of bamboo growing on the west of Pichincha, and is described as being of a milk white color, in part apparently crystalline in structure, and in part semi-transparent and gelatinous. It was seen to contain traces of the vegetable structure of the plant from which it had been extracted. On ignition it became black, and emitted pungent fumes.
An analysis of this tabasheer from the Andes showed that it contained 70 per cent. of silica and 30 per cent. of potash, lime, and water, with some organic matter. It would, perhaps, be rash to conclude from this single observation that the American bamboo produced tabasheer of different composition from that of the Old World; but the subject is evidently one worthy of careful investigation.
It was in the year 1819 that Sir David Brewster published the first account of his long and important series of observations upon the physical peculiarities of tabasheer (Phil. Trans., vol. cix., 1819, p. 283). The specimens which he first examined were obtained from India by Dr. Kennedy, by whom they were given to Brewster.
Brewster found the specimens which he examined to be perfectly isotropic, exercising no influence in depolarizing light. When heated, however, it proved to be remarkably phosphorescent. The translucent varieties were found to transmit a yellowish and to reflect a bluish white light - or, in other words, to exhibit the phenomenon of opalescence. When tabasheer is slightly wetted, it becomes white and opaque; but when thoroughly saturated with water, perfectly transparent.
By preparing prisms of different varieties of tabasheer, Brewster proceeded to determine its refractive index, arriving at the remarkable result that tabasheer "has a lower index of refraction than any other known solid or liquid, and that it actually holds an intermediate place between water and gaseous bodies!" This excessively low refractive power Brewster believes to afford a complete explanation of the extraordinary behavior exhibited by tabasheer when wholly or partially saturated with fluids. A number of interesting experiments were performed by saturating the tabasheer with oils of different refractive powers, and by heating it in various ways and under different conditions, and also by introducing carbonaceous matter into the minute pores of the substance by setting fire to paper in which fragments were wrapped.
The mean of experiments undertaken by Mr. James Jardine, on behalf of Brewster, for determining the specific gravity of tabasheer, gave as a result 2.235. From these experiments Brewster concluded that the space occupied by the pores of the tabasheer is about two and a half times as great as that of the colloid silica itself!
From this time forward Brewster seems to have manifested the keenest interest in all questions connected with the origin and history of a substance possessing such singular physical properties. By the aid of Mr. Swinton, secretary to the government at Calcutta, he formed a large and interesting collection of all the different varieties of tabasheer from various parts of India. He also obtained specimens of the bamboo with the tabasheer in situ. In 1828 he published an interesting paper on "The Natural History and Properties of Tabasheer" (Edinburgh Journal of Science, vol. viii., 1828, p. 288), in which he discussed many of the important problems connected with the origin of the substance. From his inquiries and observations, Brewster was led to conclude that tabasheer was only produced in those joints of bamboos which are in an injured, unhealthy, or malformed condition, and that the siliceous fluid only finds its way into the hollow spaces between the joints of the stem when the membrane lining the cavities is destroyed or rent by disease.
Prof. Edward Turner, of the University of London, undertook an analysis of tabasheer, the specimens being supplied from Brewster's collection (Edinburgh Journal of Science, vol. viii., 1828, p. 335). His determinations of the specific gravities of different varieties were as follows:
Chalky tabasheer. 2.189 Translucent tabasheer. 2.167 Transparent tabasheer. 2.160
All the varieties lose air and hygroscopic water at 100° C., and a larger quantity of water and organic matter (indicated by faint smoke and an empyreumatic odor) at a red heat. The results obtained were as follows:
Loss at 100° C. Loss at red heat. Chalky tabasheer. 0.838 per cent. 1.277 per cent. Translucent tabasheer. 1.620 " " 3.840 " " Transparent tabasheer. 2.411 " " 4.518 " "
Dr. Turner found the ignited Indian tabasheer to consist almost entirely of pure silica with a minute quantity of lime and vegetable matter. He failed to find any trace of alkalies in it.
In 1855, Guibourt (Journ. de Pharm. , xxvii., 81, 161, 252; Phil. Mag, , x., 229) analyzed a specimen of tabasheer having a specific gravity of 2.148. It gave the following result:
Silica. = 96.94 Potash and lime. = 0.13 Water. = 2.93 Organic matter. = trace
Guibourt criticised some of the conclusions arrived at by Brewster, and sought to explain the source of the silica by studying the composition of different parts of the bamboo. While the ashes of the wood contained 0.0612 of the whole weight of the wood, the pith was found to contain 0.448 per cent., the inner wood much less, and the greatest proportion occurred in the external wood. On these determinations Guibourt founded a theory of the mode of formation of tabasheer based on the suggestion that at certain periods of its growth the bamboo needed less silica than at other times, and that when not needed, the silica was carried inward and deposited in the interior.
In the year 1857, D.W. Host van Tonningen, of Buitenzorg, undertook an investigation of the tabasheer of Java, which is known to the natives of that island under the name of "singkara" (Naturkundig Tijdschrift voor Nederlandsch Indie, vol. xiii., 1857, p. 391). The specimens examined were obtained from the Bambusa apus, growing in the Residency of Bantam. It is described as resembling in appearance the Indian tabasheers. Its analysis gave the following result: