[ 2 9 6 ] 



SECT. XXVII. 



Some of thefe bodies melt to a coiourlefs tranfl 

 parent glafs with the borax $ for inftance, the 

 Calcareous Subitances, when pure, the Fluores.^ 

 feme of the Zeolites, &c. Others tinge the borax 

 with a green tranfparent colour •, viz. the Granate<£ % 

 Trappy iome of the Argillacc^ fome of the Mica- 

 ce<e and AJL'eflpitf : This green has its origin, partly 

 irorn a fmall portion of iron, which the Granatca: 

 particularly contain, and partly from phlogifton. 



SECT- XXVIII. 



The borax cannot diflblve but a certain quan- 

 tity of a mineral body proportional to its own. 

 Of the calcareous kind it diflblves a vaft quantity, 

 but turns at laft, when too much has been added, 

 from a clear, tranfparent, to a white, opaque flag. 

 When the quantity of the calcareous matter ex- 

 ceeds but little in proportion, the glafs looks very 

 clear as long as it remains hot ; but as foon as it 

 begins to cool, a white half opaque cloud is ken 

 to arife from the bottom, w T hich fpreads, over the 

 third, half, or more of the glafs globe, in propor- 

 tion to the quantity of calcareous matter •, but the 

 glafs or flag is neverthelefs mining, and of a glafly 

 texture when broke •, if more of this matter be 

 added, the cloud rifes quicker and more opaque, 

 and io by degrees till the flag becomes quite milk 

 white : Jt is then no more of a mining, but rather 

 flry appearance, on the furface ; is very brittle, and 

 rfa grained texture, when broke. 



£ECT. 



