of the Argillaceous Iron Ore. 263 



Upon this subject we cannot refrain from making one ob- 

 servation, which is of a nature so obvious, that were it not in 

 many cases overlooked, we should hardly have considered it 

 necessary to state it. The remark now referred to is this, that 

 the first step to be taken in procuring any ore for an assay, is 

 to select with care what is a fair average specimen of the qua- 

 lity of the ore. To do this with propriety, as it is only choos- 

 ing a small sample from a large mass, requires a considerable 

 share of discrimination and attention : and yet, to do it with 

 accuracy is a matter of the very last importance, for if a mis- 

 take be committed here, no matter how carefully the other steps 

 of the process may be performed, there still remains the greatest 

 hazard that the result may either leave a mass of rich material 

 undervalued, or perhaps the more fatal error, of causing too 

 high an estimation to be placed on an ore of indifferent qua- 

 lity. 



In most cases the ore may, without any material inconve- 

 nience, be subjected to the assay furnace, without having been 

 previously calcined. This previous calcination, however, al- 

 ways has a sensible effect in facilitating the accurate performance 

 of the assay. For if it have been omitted, an effervescence ne- 

 cessarily occurs at the commencement of the ignition, through 

 the disengagement of carbonic acid from the carbonates of iron, 

 lime, &c. and also through the escape of gas arising from 

 the decomposition of the carbonaceous ingredient : the mix- 

 ture, in consequence, is apt to be derauged, and a portion of it 

 may even be thrown upwards out of the sphere of the flux al- 

 together, so that though this may also be reduced, it is not ab- 

 sorbed by the scoria, and transmitted to the metallic button. 

 Calcination becomes particularly important when the ore hap- 

 pens to contain an unusually large proportion of carbonaceous 

 or coally matter, as is generally the case with the black-colour- 

 ed varieties ; for if the carbonaceous particles were allowed to 

 remain diffused throughout the mixed mass, they would not 

 fail to exercise a powerful influence in rendering it refractory, 

 and in preventing the particles of reduced metal from meeting 

 in a imited mass. 



The ore may be calcined in the following manner. Reduce 

 from one to two hundred grains of it to a fine powder, and in- 



