102 PHILOSOPHICAL TRANSACTIONS. [aNNO 1791. 



which makes its specific gravity to be very nearly = 2.188. Mr. Cavendish, 

 having tried this same parcel when become again quite dry, found its specific 

 gravity to be = 2.169. 



Treated with water. — § 2. (a) This tabasheer, put into water, emitted a 

 number of bubbles of air ; the white opaque bits became transparent in a small 

 degree only, but the bluish ones nearly as much so as glass. In this state the 

 different colour produced by reflected and by transmitted light was very sensible. 

 (b) Four bits of this substance, weighing together, while dry and opaque, 4.1 

 gr., were put into distilled water, and let become transparent ; being then taken 

 out, and the unabsorbed water hastily wiped from their surface, they were again 

 weighed, and were found to equal 8.2 gr. In exper. ^ 1. (g), 75.7 gr. of this 

 substance absorbed 69.5 gr. of distilled water. 



(c) Four bits of tabasheer, weighing together 3.2 gr. were boiled for 30™ in 

 -1- an oz. of distilled water in a Florence flask, which had been previously rinced 

 with some of the same fluid. This water, when become cold, did not show any 

 change on the admixture of vitriolic acid, of acid of sugar, nor of solutions of 

 nitre of silver, or of crystals of soda ; yet, on its evaporation, it left a white 

 film on the glass, which could not be got off by washing in cold water, nor by 

 hot marine acid ; but which was discharged by warm caustic vegetable alkali, 

 and by long ebullition in water. Upon these bits of tabasheer, another -i- oz. of 

 distilled water was poured, and again boiled for about -i- an hour. This water 

 also on evaporation left a white film on the glass vessel, similar to the above. 

 The pieces of tabasheer having been dried, by exposure to the air for some days 

 in a warm room, were found to have lost -j-l of a gr. of their weight. To as- 

 certain whether the whole of a piece of tabasheer could be dissolved by boiling 

 in water, a little bit of this substance, weighing -|3_ of a gr. was boiled in 36 oz. 

 of soft water for near 5 hours consecutively ; but being afterwards dried and 

 weighed, it was not diminished in quantity, nor was it deprived of its taste. 



IVith vegetable colours. — ^ 3. Some tabasheer, reduced to fine powder, was 

 boiled for a considerable time in infusions of turnsole, of logwood, and of dried 

 red cabbage, but produced not the least change in any one of them. 



j4t the fire. — § 4. (a) A piece of this tabasheer, thrown into a red-hot 

 crucible, did not burn or grow black. Kept red-hot for some time, it under- 

 went no visible change ; but when cold, it was harder, and had entirely lost its 

 taste. Put into water it became transparent, just as it would have done, had it 

 not been ignited, (b) 6.4 gr. of this substance, made red-hot in a crucible, 

 were found, on being weighed as soon as cold, to have lost ~v of a gr. This 

 loss appears to have arisen merely from the expulsion of interposed moisture ; 

 for these heated pieces, on being exposed to the air for some days, recovered 

 exactly their former weight, (c) A bit of this substance was put into an earthen 



