ON THE ANHYDROUS SULPHATE OV LIME. 195 



In the fame manner it is, that, in the blue carbonate of copper, Blue carbonate 

 which, according to the inveftigations of Mr. Prouft, appears of C0 PP eu 

 to contain a contiderable quantity of water, far fuperior to that 

 which exifts in the green carbonate, the cryftals feem to pafs, 

 at their furface, into the ftate of green carbonate, by the mere 

 lofs of a certain portion of their conftituent water. This fpecies 

 of decompofition is fometimes even fo considerable in them, 

 that it exifts, for example, amongft the fpecimens in large and 

 fuperb cryftals which come from Siberia, cryftals, of which the 

 form having undergone no change, belongs to the blue carbo- 

 nate, but which have entirely paffed, throughout their whole 

 fubftance, into the ftate of green carbonate. 



I am fully perfuaded, that when water is once confidered Water «s of great 



ii.. a. ■ • .1 />,• c importance as an 



and admittted as a conftituent part in the compohtion ot nu- j ngre dient which 

 merous mineral fubftances, it will foon be acknowledged to modifies the pro- 

 contribute greatly, by its prefence or its abfence, to the differ- P erties ° 

 ence which fubfifts between feveral ftones : thus I am ftrongly 

 inclined to believe that the carbonate of lime of flow folution, 

 the hardnefs and fpecific gravity of which are fo much fuperior 

 to the fame characters in the ordinary carbonate of lime, differs 

 from this latter perhaps only by a difference in the water of 

 compofition. Moll certainly this difference cannot proceed 

 either from the prefence of argil, or from that of magnefia. I 

 know fome dolomies which certainly do not contain any trace 

 of argil, whilft, at the fame time, I know carbonates of lime, 

 which are highly charged with magnefia, and which, never- 

 thelefs, are very fpeedily diffolved in the acids : Of the num- 

 ber of thefe latter are, for example, mod of the calcareous 

 fpars with a pearly reflection and greafy afpecl. 



- I am much inclined alfo to think, that the fpecies of Chalce- Cacholong pro- 

 dony, named cacholong, may owe its difference from the com- p J cu ^ W p c * p e * r , 

 noon chalcedony only to the circumftance, that the latter con- ties to the ab- 

 tains water of compofition of which the chacolong is deftitute ; fence of water * 

 and that the tranfition of the chalcedony into this ftate, and 

 fubfequently into the hydrophanes, depends, in a great meafure, 



upon the lofs of this water. The probability of this opinion 

 remains to be fettled by future obfervations. 



O 2 IX. Awlyfis 



