~ and Tron-Stones by Pufions 239 
‘In fuch an infinity of variation it is difficult to arrange the 
combinations of which thefe fubftances are capable. To des 
rive the name of a clafs, or genus, from the predominancy of 
an earth, feems moft eligible; and to confider thofe as va- 
rieties of the fame clafs, which are altered by the proportion 
of the fecond and third mixtures. Again, each of thefe va4 
Fieties are fufceptible of a multiplicity of modifications before 
an earth is fo far diminifhed as to give an afcendency to an- 
other, or before the third rank ‘of proportion has affumed 
that of the fecond or firft. The fimple combination of the 
earths, and their degrees of predominancy, may be thus ar- 
ranged :-—~ 
rft Variety, 2d Variety. 
Iron = - fron 
Clay - + Clay 
Lime’ -. + «Silex 
Silex---<»~ 3; Lime 
fron - -  -Fron 
Caleareous iron-ftone ae 4 r a ‘e 
Silex +) =) Chy 
Iron - - Iron 
Silex - - _Salex 
Lime - =~ Clay 
Clay = = 
Argillaceous iron-ftone 
———- 
As thefe become varied, they form 
the clafs of equalifed mixture, 
Siliceous iron - ftone 
'¢ 
5 
@ 
Qo 
To affay any of thefe varieties, a flux peculiar to the na- 
ture of the mixture is neceflary; fo that the changes of pro- 
portion in the folvent ought to extend to feven, including 
the clafs of equalifed mixtures, in order that the precife fame ~ 
quality of crude iron may be produced from all the varieties 
of iron-ftone. The modification of each variety will be: 
found to be fufficiently accurate, if affayed by the flux pecu- 
Kiar to itfelf. The arrangement of the three claffeés of ores 
into two varieties, each forming a diftin@ {tage of combina- 
"tion, indicated by the predominancy of the firft and fecond 
earth, are, with the neutral clafs, fuffiiciently minute for any 
purpofe in the affay-furnace, and are fufficient to form an 
7 accurate 
