14 Elements of Mineralogy. 



alum, as gypfum in that cafe would be formed* 

 which is infoluble in the marine acid, but 

 pure magnefia, that is, free from aerial acid* 

 does not precipitate lime water. 



Siliceous Earth feems alfo to have fome 

 affinity to the argillaceous, for although it 

 cannot be brought into fufion by the argilla-^ 

 ceous, yet when melted by fixed alkalis 

 it ats on the argillaceous Earth of the cruci- 

 bles and diflblves it; now fixed alkalis fmgly, 

 cannot melt argillaceous Earth ; to fay no- 

 thing of the hardening power of argill and 

 filiceous Earths, when mixed together and 

 heated. 



Iron in a more or lefs dephlogifticated ftate* 

 being found in fome proportion mixed or united 

 with almoft all forts of Earths and Stones, de- 

 ferves alfo to have its affinities to tkem men- 

 tioned, it is much more fufible thaix any of 

 them, and may therefore be confidered as a 

 menftruum. Mr* diehard has found that an 

 hundred parts of calx of iron are capable 

 of melting foiir hundred of calcareous, fifty 

 of argillaceous, thirty- three of filiceous and 

 twenty-five of magnefian Earths, it acts 

 ftill more powerfully on lefler proportions of 

 thefc Earths. 



Hence, 



