33 
trofti 
That argillaceous and siliceous earths— argillaceous and 
magnesian earths — siliceous and magnesian earths, would 
not melt in whatever proportions they were mixed* 
That siliceous and calcareous earths— argillaceous and 
calcareous earths, by very strong heat might be vitrified^ 
but not into a perfect and thin glass. 
That when the earths are calcareous, argillaceous and 
magnesian, it requires that the lime should be in a double 
portion to make a glass* 
That no glass can be produced if the clay-earth or the 
magnesian earth predominate. 
* That calcareous earth, argillaceous earth, and siliceous 
earth — or, calcareous earth, magnesian earth, and siliceous 
earth — -can be brought into perfect fusion if the calcareous 
earth somewhat predominate. And that by means of a 
strong heat, a perfect glass may be produced by siliceous^ 
argillaceous and magnesian earths alone, without lime i 
and that this is the only combination he tried, in which 
limestone earth was not absolutely necessary in the mix- 
ture, to make glass. 
He further ascertained, that all the metallic oxyds, and 
of course that of iron, assisted in producing fusion i also, 
that common clay contains one half or more of its weight 
usually of sand, intimately mixed* 
Hence limestone earth, or calcareous earth, may be re- 
garded as the substance most lit in an economical point 
of view to bring other earths into thin fusion ; for which 
purpose it should be in the proportion of 1 1-2 or nearly 
2 to 1 of that earth which predominates in the iron-stone. 
Hence, if clay predominate in the iron-stone, (or earth 
of which pure clay is the basis) the flux is limestone : and 
on the contrary if the iron be mixed with limestone, the 
proper flux is not limestone, but clay* 
Also, that herein consists much of the practical know- 
ledge of assorting ores, namely to mix together such ores ? , 
E 
