VOL. LXX.] PHILOSOPHICAL TRANSACTIONS! GOQ 



by filtration. Having the liquor in the basin now clear, put into it a piece of iron, 

 bright and free from rust, and at least 1 oz. in weight, and leave them together for 

 24 hours; the copper will be found precipitated, principally on the surface of the 

 iron, and sometimes in a powder at the bottom of the basin. 



Decant the fluid from the copper and iron with great care into another basin, 

 so that as little as possible or none of the copper be carried along with it. 

 Wash the metals in a pint of water; let them subside perfectly, and pour this 

 water into the 2d basin, with the same care, repeat the washing 3 times. If 

 any copper be found in the 2d basin, let the washings stand in it for -^ an hour, 

 so that the metal shall subside; decant the fluid carefully off, and return the 

 copper into the first basin. Pour on the copper and iron 1 oz. of vitriolic acid, 

 and 2 oz. of water; lot them stand together for J- of an hour, or till the copper 

 shall be easily separable from the iron. Separate the copper from the iron, 

 taking great care none be lost; the remaining iron may be laid aside. Pour the 

 acid from the copper, after it has subsided, into the 2d basin, and wash the 

 copper with a pint of water, and repeat the washing 3 times, as before 

 directed. 



Great care is to be taken, in decanting both the acid and washings into the 

 2d basin, that none of the copper goes along with them, and lest any should, 

 they ought to stand for x an hour in the 2d basin, and be decanted from it also 

 with care, and if any copper is found at the bottom, it is to be washed and added 

 to the rest. The copper is now to be dried and weighed, and gives the proportion 

 contained in the ore. 



Observations on the above process. — It was about 20 years before that Dr. F. 

 contrived some methods of assaying ores, which might avoid tedious and trouble- 

 some roastings and fusions in great degrees of heat, which require a dexterity 

 which is only to be acquired by great practice, and which, after all, form a 

 process that is often various in the result, and seldom shows the substances 

 contained in the ore, excepting the metal. The principles on which these pro- 

 cesses depend, as far as regards copper ores, are, 



1°. Metals are attracted more strongly by acids than by sulphur, with which 

 they are often combined in their ores. In consequence, if a metal be combined 

 with sulphur in an ore, it may be separated by applying an acid, which will 

 unite with the metal, and separate the sulphur. The metal may generally be 

 separated from the acid in its metallic form by means of another metal, which 

 attracts the acid more strongly. 



2°. Arsenic unites with vitriolic, nitrous, and muriatic acids, forming a cor 

 rosion or compound not soluble in water; whereas most other metals may be 

 united with one of these acids, or a mixture of them, so as to form a compound 

 soluble in water: therefore, if there be arsenic combined with a metal in an ore, 



VOL. XIV. 4 I 



