114 AGniCUT-TUIlAL MtTSEUM 



here be arscrj.' combined A>ilh a metal in an ore, if it 

 bo dissolved in sticli aeid diluted with wUter, the arsenic 

 will fall to the bot:om in a white jjovvder, or in crystals, 

 uul the solution, bring- poured off, will contain the nietal^ 

 ivhieii inay be separated from the aeid by another metal, 

 .is before. 



Thirdly. The calces of nicials may be dissolved in 

 acids, whether tlicy be pure (ofuhii-h there arc few in- 

 stances in ores) or conihjtied with giis, respirsiiUe an> 

 or other vapours r thereroic, if the metal iri an ore be in 

 the form of a calx, we ?iiay find an acid which will dis- 

 solve it^ and we vhtiy afterwards precipitate it in its me- 

 tallic form, as before. 



Fourtlily. When an ore is to be assayf^d, it should be 

 separated IVom the quartz, spars, and other earthjMiiat- 

 ters, with which it is often mixed, as perfectly as possi- 

 ble ; however, after all our care, there will often be a 

 part of them bo intimately iiiixed wi^h tfie ore, that it 

 cannpt bt; entirely cleared. Many of these earthy mat- 

 tei s do not dissolve readily in acids: therefore, if the me- 

 tal of an ore be dissolved in an aeid, so as to form a com- 

 pound soluble in water, the solution of the metal may be 

 poured oft", leaving such earthy matters behind. 



Fifthly. If the earthy matter should dissolve in the acid^ 

 it is seldom to be precipitated by a metal : therefoi'e, if 

 both earth and metal be dissolved, on the application 6t 

 another metal, v^ hich attracts the acid more stroiifflv. 

 that which was combiatd with the acid will be preeipita- 

 ted, and the earth left in the solution. 



yixthly. Acids attract the metals with different pow- 

 ers: therefore, if two metals be combined with an aeid, if 

 we apply to the solution amass of that which attracts 

 the acid strongest, the otiier will be precipitated. The 

 mass being weighed belbre and after the precipitation, 

 the dilu I cnee \\ ill be the quantity of additional metal 

 cisi?o;v(d: if, there fure, we pour oiV the liquor from the 

 ] recipitatc, and ajiply another metal, which attracts the 

 ac.d stll ni! i:c strongly, t:;e second metal will be preei- 

 p.tu'.eJ ; which, lc:iig weighed, aiid the weight lost from 



