t 47 ] 



agate, fardonyx, agate, cats-eye, &c. all of 

 which decay by expofure to air. 



d. Jafper is lefs hard than flint, and melts more 

 readily into glafs, but does not decay in the air. 

 It is of a cryftal bafis of various colors, and 

 always opaque, as the heliotrope, the green, 

 red, yellow, black jafper, &c. 



K. Gems are cryftals of various colors, generally 

 found in fmall bodies, hard, bright and radiant, 

 as the diamond, ruby, faphire, topaz, beryl or 

 bluifti green topaz, chryfolite or yellowim green 

 topaz, emeral, garnet. From the difficulty of 

 procuring thefe bodies, few experiments have 

 hitherto been made upon them ; the experiments 

 on diamonds by Dr. Darcet, prove them to be 

 volatile by heat. 



II. SALTS. 



SALTS are foluble in water, and recover- 

 able by evaporation to their priftine angular 

 form not inflammable nor ductile. 



ii The fimple faks are either alkaline or 

 acid (/). 



A. Alkaline salts turn the fyrup of violets, 

 or an infufion of purple flowers, of a green 

 color, and effervefce with acid falts. 



a. Foffil alkali, fo called from its being found 

 in the earth, in large ftrata, but in a compound 

 ftate. It is alfo in fea fait, and may be pro- 



{f) Some of thefe falts are not native productions ; but as 

 an acquaintance with thefe fubftances may prove an intro- 

 duction to the knowledge of many ufeful chemical fads, a 

 more general account is here given of them. 



cured 



