34 Dr. fordyce’s Method of 
Secondly, Arfenic unites with vitriolic, nitrous, and 
muriatic acids, forming a corrofion or compound not fo- 
luble in water; whereas moft other metals may be united 
with one of thefe acids, or a mixture of them, fo as to 
form a compound foluble In water: therefore, if there 
be arfenic combined with a metal in an ore, if it be dif- 
folved in fuch acid diluted with water, the arfenic will 
fall to the bottom in a white powder or cryitals, and the 
folution being poured off will contain the metal, which 
may be feparated from the acid by another metal as 
before. 
Thirdly, the calces of metals may be diflolved in acids, 
whether they be pure (of which there are few inftances 
in ores) or combined with gas, refpirable air, or other 
vapours ; therefore, if the metal in an ore be in the form 
of a calx, we may find an acid which will diflblve it, and 
we may afterwards precipitate it in its metallic form as 
before. 
Fourthly, When an ore is to be aflayed, it fhould be 
feparated from the quartz, fpars, and other earthy mat- 
ters, with which it is often mixed, as perfebtly as pofli- 
ble ; however, after all our care there will be often a part 
of them fo intimately mixed with the ore, that it cannot 
be entirely cleared. Many of thefe earthy matters do 
not diflblve readily in acids : therefore, if the metal of an 
ore 
