VOL. LXXXl.] PHILOSOPHICAL TRANSACTIONS. 103 



crucible, surrounded with sand, and kept red-hot for some time ; when cold, it 

 was still white, both exteriorly and interiorly, (d) Thrown into some melted 

 red-hot nitre, this substance did not produce any deflagration, or seem to sufi^er 

 any alteration, (e) A bit exposed on charcoal to the flame of the blow-pipe did 

 not decrepitate or change colour ; when first heated it diffused a pleasant smell ; 

 then contracted very considerably in bulk, and became transparent ; but on con- 

 tinuing the heat it again grew white and opaque, but seemed not to show any 

 inclination to melt per se. Possibly however it may suffer such a semi-fusion, 

 or softening of the whole mass, as takes place in clay when exposed to an intense 

 heat ; for when the bit used happened to have cracks, it separated during its con- 

 traction, at these cracks, and the parts receded from each other without falling 

 asunder. If, while the bit of tabasheer was exposed to the flame, any of the 

 ashes of the coal fell on it, it instantly melted, and small very fluid bubbles were 

 produced. That the opacity which this substance acquires on continuing to heat 

 it after it has become transparent, is not owing to the fusion of its surface by 

 means of some of the ashes of the charcoal settling on it unobserved, appeared 

 by its undergoing the same change when fixed to the end of a glass tube, in the 

 method of M. de Saussure. 



With acids. — § 5. (a) A piece of tabasheer, weighing 1.2 gr. was first let 

 satiate itself with distilled water; its surface being then wiped dry, it was put 

 into a matrass with some pure white marine acid, whose specific gravity was 1.13. 

 No effervescence arose on its immersion into the acid; nor did this menstruum, 

 even by ebullition, seem to have any action on it, or itself receive any colour. 

 The acid being evaporated, left only some dark coloured spots on the glass. 

 These spots were dissolved by distilled water. No precipitation was produced in 

 this water by vitriolic aid, or by a solution of crystals of soda. The bit of taba- 

 sheer washed with water, and made red hot, had not sustained any loss of weight. 

 The pores of the mass of tabasheer were filled with water before it was put 

 into the acid, to expel the common air contained in them, and which would have 

 made it impossible to ascertain with accuracy whether any effervescence was 

 produced on its first contact with the menstruum. 



(b) Another portion of tabasheer, weighing tO.2 gr. was boiled in some of 

 the same marine acid. Not the least precipitate was produced on saturating this 

 acid with solution of mild soda. This tabasheer also, after having been boiled 

 in water, and dried by exposure for some days to the air, was still of its former 

 weight. 



§ 6. This substance seemed in like manner to resist the action of pure white 

 nitrous acid boiled on it. 



§ 7. (a) A bit of tabasheer weighing 0.6 gr. was digested in some strong 

 white vitriolic acid, which had been made perfectly pure by distillation. It did 



