March 24, 1887] 



NA rURE 



489 



and season upon the production of the substance are 

 questions which do not seem as yet to have been accu- 

 rately investigated. 



Dr. Russell found that the bamboos which produce taba- 

 sheer often contain a fluid, usually clear, transparent, and 

 colourless or of greenish tint, but sometimes thicker and 

 of a white colour, and. at other times darker and of the 

 consistency of honey. Occasionally the thicker varieties 

 were found passing into a solid state, and forming 

 tabasheer. 



Dr. Russell performed the interesting experiment of 

 drawing off the liquid from the bamboo-stem and allowing 

 it to stand in stoppered bottles. A " whitish, cottony 

 sediment " was formed at the bottom with a thin film of 

 the same kind at the top. When the whole was well 

 shaken together and allowed to evaporate, it left a residue 

 of a whitish-brown colour resembling the inferior kinds 

 of tabasheer. By splitting up different joints of bamboo 

 Dr. Russell was also able to satisfy himself of the 

 gradual deposition within them of the solid tabasheer 

 by the evaporation of the liquid solvent. 



In 1791, Mr. James Louis Macie, F.R.S. (who afterwards 

 took the name of Smithson), gave an account of his 

 examination of the properties of the specimens of taba- 

 sheer sent home by Dr. Russell (Phil. Trans, vol. Ixx.ki., 

 '79') P 36S). These specimens cime from \'ellore, 

 Hydrabad, Masulipatam, and other localities in India. 

 They were submitted to a number of tests which 

 induced Mr. Macie to believe that they consisted princi- 

 pally of silica, but that before calcination some vegetable 

 matter must have been present. A determination of the 

 specific gravity of the substance by Mr. Macie gave 2'l8S 

 as the result ; another determination by Mr. Cavendish 

 gave 2 '169. 



In this same paper it is stated that a bamboo grown in 

 a hot- house at Islington gave a rattling noise, and on 

 being split open by Sir Joseph Banks yielded, not an 

 or-jinary tabasheer, but a small pebble about the size of 

 half a pea, externally of a dark brown or black colour, 

 and within of a reddish-brown tint. This stone is said to 

 have been so hard as to cut glass, and to have been in 

 parts of a crystalline structure. Its behaviour with re- 

 agents was found to be different in many respects from 

 that of the ordinary tabisheer ; and it was proved to 

 contain silica and iron. The specimen is referred to in 

 a letter to Berthollet published in the Annaks dc 

 Chiinic for the same year (October 1791). There may 

 be some doubt as to whether this specimen was really 

 of the nature of tabasheer ; if such were the case, it would 

 seem to have been a tabasheer in which a crystalline 

 structure had begun to be set up. 



In the year 1S06, MM. Fourcroy and Vauquelin gave 

 an account of a specimen of tabasheer brought from 

 South America in 1804 by Humboldt and Bonpland 

 [^Miiii. tie I'l/ist., 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 colour, in part 

 apparently crystalline in structure, and in part semi-trans- 

 parent 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 taba- 

 sheer of different composition from that of the Old World ; 

 but the subject is evidently one worthy of careful in\ esti- 

 gation. 



It was in the year 1819 that Sir David Brewster 

 published the first account of his long and important 

 series of obser\-ations upon the physical peculiarities of 

 tabasheer (Phil. Trans., vol. ci.x., 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 de- 

 polarising light. When heated, however, it proved to be 

 remarkably pliospliorcscent. The translucent varieties 

 were found to transmit a yellowish and to reflect a bluish- 

 white light — or, in other words, to exhibit the pheno- 

 menon of opalescence. When tabasheer is slightly wetted, 

 it becomes white and opaque ; but when thoroughly 

 saturated with water, perfectly transparent. 



By preparing prisms of difterent 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 com- 

 plete explanation of the extraordinary behaviour exhi- 

 bited by tabasheer when wholly or partially saturated 

 with fluids. A number of interesting experiments were 

 performed by saturating the tabasheer with oils of 

 ditlerent refractive powers, and by heating it in various 

 ways and under difterent conditions, and also by intro- 

 ducing 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 mani- 

 fested 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 difterent varieties 

 of tabasheer from various parts of India. He also obtained 

 specimens of the bamboo with the tabasheer in situ. In 

 182S he published an interesting paper on " the Natural 

 History and Properties of Tabasheer" {Edinburgh Journal 

 of Science, vol. viii., 1S2S, 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 (Edinburg/i Journal 

 of Science, \o\. viii., 1S28, p. 335). His determinations 

 of the specific gravities of different varieties were as 

 follows : — 



Chalky tabasheer ... 

 Translucent tabasheer 

 Transparent tabasheer 



2-:67 

 2'i6o 



All the varieties lose air and hygroscopic water at 100" 

 C, and a larger quantity of water and organic matter (in- 

 dicated by faint smoke and an empyreumatic odour) at a 

 red heat. The results obtained were as follows : — 



Lo.^s at 100° C. Loss at red heat 



Chalky tabasheer 0838 per cent, i -277 per cent. 



Translucent tabasheer i'620 ,, ,, 3840 ,, ,, 



Transparent tabasheer 2'4ii ,, ,, 4'5'8 ,, ,, 



Dr. Turner found the ignited Indian tabasheer to con- 

 sist almost entirely of pure silica with a minute quantity 



