250 Dr Colquhoun on the Assay 



but the clouded state of the sky prevented its being visible. 

 The same cloudiness extended all along the Ganges as far as 

 Calcutta, a distance of 3° 22' of latitude, and perhaps farther. 



Art. VIII. — On the Assay of the Argillaceous Iron-Ore. 

 By Hugh Colquhoun, M. D, Communicated by the Author. 



The assay of an ore of iron is the process of subjecting a 

 small portion of it, as an average specimen of the mass, to the 

 test of chemical analysis, in order to discover the amount and 

 value of metal which it may contain, together with the nature 

 and relative proportions of those earthy ingredients with which 

 the metal is associated. If this analysis be conducted by so- 

 lution in acids, and then obtaining each ingredient in a sepa- 

 rate form, so as to ascertain the constitution of the ore with 

 scientific precision, it is styled the humid assay. But if the 

 analysis be made by merely reducing the ore in a crucible, 

 either per se or associated with a flux, and then examining the 

 metallic and scoriaceous mass that results from this reduction, 

 it is termed the dry assay. 



Each of these processes has for its object the important pur- 

 pose of estimating the metallic richness of any given mass of 

 ore, and the expense in fuel and flux which it will cost to ex- 

 tricate the iron. Each method possesses certain advantages 

 that are peculiar to itself, and each is also marked by its own 

 inconveniences. For although the humid assay, or chemical 

 analysis, affords the only sure method of ascertaining with 

 precision the nature and relative proportions of the ingredients 

 in any ore, yet it requires more delay, and perhaps more care 

 than the smelter is willing to bestow ; and it may also some- 

 times demand a greater acquaintance with the science of che- 

 mistry than he possesses. On the other hand, the dry assay, 

 conducted by a man of practical experience, will seldom fail 

 to give a tolerably accurate view of the amount of metal in 

 an ore, and of the general character of its earthy ingredients. 

 It is a process requiring no great exertion of patience or at- 

 tention, and as being perhaps more congenial with his general 

 habits, it is almost invariably preferred by the metallurgist. 



