ON THE ANHYDROUS SULPHATE OF LIME. \9$ 



the preceding fpecimen ; its lamboc are larger, their rectan- 

 gular form is more perceptible, and feveral of them have a 

 pearly reflection. 



Of two other pieces of the fame fubftance, in the cabinet of Otherfpeclmens. 

 Mr. Greville at London, which appear to me to belong to 

 the anhydral fulphate of lime of the falt-works in the canton 

 of Bern, and both which are perfectly pure, the one is white 

 with a little of a blueifh caft, the other has the fame blueifh 

 tinge, but deeper, and greatly refembles in colour the pale 

 blue fapphire, known by the name of water fapphire. Both 

 have a coarfe granulated texture, and are. compofed of a com- 

 bination of rectangular lamina, which crofs each other in dif- 

 ferent directions, as may eafily be difcerned with the naked 

 eye. But the laminae of that in which the blueifh colour is 

 the molt intenfe, prefent befides fo lively a pearly reflection, 

 that it might eafily, at firft fight, be miftaken for a mafs of 

 zeolite ftilbite. Rectangular laminse, of fome thicknefs, may 

 be feparated from it, which, like the cryftals before defcribed, 

 are eafily divided in every direction. 



The fpecific gravity of the anhydrous fulphate of lime, Specific gravity, 

 mixed with common fait, proved to be 2940. That of the 

 fpecimens which I mentioned in Mr. Greville's cabinet, 

 namely, that in which the laminae had the flrong pearly re- 

 flection, was 29.57, and the other 2929. Of the two of Vul- 

 pino, the moft compact was 2951, and the other 2933. 



The hardnefs of this fubftance, in all the fpecimens, Is fome- Hardnefs. 

 what fuperior to that of the carbonate of lime ; in all of them 

 alfo the anhydrous fulphate of lime is fufible by the blow-pipe 

 without ebullition, and affords an opaque glafs. 



There is a marked difference between them, with refpect to phofphoref- 

 the phofphorefcence, upon an heated fhovel. The anhydrous cence » 

 fulphate of lime of Vulpino, gives a pretty flrong orange-co- 

 loured light ; that mixed with common fait, affords a very 

 faint bluifh light ; that of the falt-works of Bern, none at all j 

 and laflly, that which I mentioned as containing actinote, with 

 attractive oxide of iron, &c. gives a light fomewhat more red- 

 difh than that of Vulpino. 



Gypfum deprived of water, or anhydrous fulphate of lime, The abfence of 

 therefore, poffeffes characters altogether different from thofe ^ater renders 

 of the fulphate of lime which contains that liquid; and as in altogethe/dWer- 

 thefe two ftones the fulphuric acid and the lime exift in theent. 



Vol. II.— -July, 1802. O fame 



