S54 Dr Colqiihoun on the Assay 



from poverty in metal or the predominance of one of its earthy 

 ingredients over the others, it will be proper to increase the ac- 

 tivity of the above mixture, by the addition of about 10 parts 

 of fluor spar or calcined borax. * 



Having thus stated the general nature of the operation 

 which it is the object of the assayist to perform, we may next 

 proceed to the details of this branch of the metallurgic art, in 

 examining which we shall adopt the following order. We 

 shall first consider what general rules have been established 

 regarding the fusibility of the several earths which nature or 

 art has associated with the oxide of iron in the smelting fur- 

 nace. After determining what mixtures form the most fusi- 

 ble compounds, we shall next advert to the means of procur- 

 ing in a state of purity any of those substances which the as- 

 sayist's exigencies may require. We shall then consider the 

 mode of subjecting the adjusted compound of ore and flux to 



• Many different recipes for compounding a general mixture for assaying 

 iron-ores may be met with in chemical and metallurgic works ; but we 

 have seen few that are deserving of commendation. Bergman, for instance, 

 mentions the following heterogeneous mixture for assaying iron-ores as 

 having been long in use among the Swedish metallurgists, and as being 

 held in high estimation. 



To 100 parts of ore, 

 100 parts of sal ammoniac. 

 < 100 tartar. 



100 glassgall. 



50 borax. 



50 charcoal dUst. 



200 black flux. 



All these ingredients, after being well intermixed, to be put into an un- 

 prepared crucible, and covered with common salt. 



Chaptal's general flux for assaying iron-ores consists of. 

 To 200 grains of ore, 

 400 borax. 



40 slacked hme. 



200 nitre. 



The whole mixture to be heated intensely for half an hour in a crucible 

 lined inside with charcoal powder. There can be little doubt that in most 

 assays performed with either of these fluxes, a considerable portion of oxide 

 of iron would be retained in a state of permanent combination by the scoria. 

 But independently of this circumstance, the violent commotion into which 

 the whole materials of the assay would be thrown in consequence of the 

 copious extrication of elastic matter from the sal ammoniac, tartar, nitre, 

 &c. would of itself seem sufficient to render every assay made with these 

 fluxes unsatisfactory. 3 



