38 ACCOUNT of a MINERAL 



12. The cryftal in its perfedl condition feems to be a flatted 

 hexagonal prifm, having two broad (ides, with two intervening 

 narrow ones, and terminated at either end by a quadrangular 

 pyramid, which, in Tome cafes, conftitutes the larger part of the 

 cryftal. When the cryftallization goes on at great leifure, the 

 cryftals are often diftindl and folid. of no inconfiderable magni- 

 tude ; but more commonly with a quicker depofition, they are 

 more flender and delicate and are attached to each other in fuch 

 a manner as to afTume a foliaceous form of beautiful appear- 

 ance, refembling feme of the fern tribe in their pinnated frons, 

 to fpeak botanically ; but in this arrangement, a confiderablc 

 diverfity occafionally happens. 



13. The cryftals obtained from calcined barytic fpar, in the 

 manner now defcribed, diifolve in water, and impart the qua- 

 lities of barytic water ; they change vegetable colours to a 

 green, they unite with acids without effervefcence, and gene- 

 rate with the muriatic and fulphuric. compounds fimilar to the 

 iulphate and muriate of barytes j hence 1 infer they confift of 

 pure barytes. 



14. These cryftals are perfedly tranfparent and colourless, 

 but when expofed to the air, become white, opaque and effer- 

 vefcent, lofing during this change nearly 30 per cent, of their 

 weight. Subjecfted to the heat of boiling water, they undergo 

 the aqueous fufion and become fluid ; from which ftate, if al- 

 lowed to cool flowly, they concrete into a folid cryftalline mafs. 

 When a ftronger heat is applied, and continued till all the moi- 

 fture is difllpated, there remains a white powder, lighter by 

 one half than the cryftals employed, which, urged by the 

 heat produced by the blowpipe, is malted with more difficulty 

 than the native carbonate. 



15. The folubility of thefe crvftals in water furprifed me a 

 good deal. One ounce of diftllled wart^r, at temperature 60, 

 diffolves aimoft twenty-five grains, while boilmg water appears to 



I be 



