S Elements of Mineralogy. 



4 th - The ftrongeft heat barely hardens it, 

 but does not give it the qualities of lime, 

 nor melt it, while fingle, or accompanied 

 only with magnefia or iiliceous Earth ; but 

 mixed with calcareous, it runs into fufion 

 very" readily, and hence Mr. Gerhard has 

 found it fufible in a crucible of chalk, but 

 not in one of clay ; fi^ed alkalis do not pro- 

 mote its fufion, but borax and microcofmic 

 fait diflblve it, the firft with fcarce any, and 

 the latter with a more notable efFervefcence. 

 Calces of lead affecl: it fomething lefs than 

 they do calcareous Earths. 



Siliceous Earth. 



i ft * This is by fome called cryflaline^ 

 quartzy, or verifiable Earth, as it is that of 

 which glafs is ufually formed ; its fpecific 

 gravity is 2,65, and confequently it is the 

 heavieft of all the fimple Earths, except the 

 barytes. 



It feems lefs foluble irj water than any 

 yet in the common temperature of the 

 atmofphere ten thoufand parts of water may 

 contain one of this Earth ; and in very high 

 degrees of heat, much exceeding that at; 

 which water ufually boiL-., it feems foluble in 

 a much greater proportion? 



3 d ' It 



