98 president's address — section b. 



as far as they arc not either volatilised or oxidised and scorified (which 

 they will all be long before the copper, on account of their appreciably 

 greater heat of combustion), and as far as they have a lesser heat of 

 combination with sulphur than copper — are reduced into their metallic 

 states by the first copper formed. Hence a small amount of the latter 

 will serve to collect a relatively large portion of certain of these as- 

 sociated elements. The metals are concentrated in some ratio to the 

 quantity of bottoms produced, so that the amount of the latter is of 

 great importance. Gold may thus be extracted in its totality in about 

 14 per cent, of bottoms. But the sclecteur allows the correct pro- 

 portion to be well approximated, dependent on some experience being 

 had with the particular matte treated, for the various impurities 

 quantitatively predispose or indispose one another for reduction. 

 The apparatus is the most ingenious representative of the mechanical 

 aids to pneumatic treatment which has been yet devised, but it has 

 not come into use outside of its French home. Fortunately, impure 

 mattes are not common in districts where the converter process is most 

 extensively employed at the present time. 



Elimination of Impurities &?/ the Pneumatic Process. — Of para- 

 mount importance is the general ease and thoroughness with which 

 the pneumatic process eliminates current impurities from copper, even 

 without the formation of bottoms. From the practical manipulative 

 point of view alone, this feature constitutes a wonderful improvement 

 over the older treatment methods. Though known in a general way 

 since the time of the first Manhes experiments, the subject has only 

 of recent years been more closely investigated, and is far from being 

 finally dealt with. The amount of chemical analysis involved is ex- 

 treme, and satisfactory parallel or congruous conditions for analytical 

 research are unattainable. Comparative working tests are mutually 

 exclusive, so to say, since no specific bulk or parcel of matte can be 

 tested by both methods. Moreover, the distribution of the impurities 

 is perplexingly irregular in both mattes and copper, so that insurmount- 

 able obstacles arise, even from the sheer impossibility of securing truly 

 representative average samples. However, in fairly definite terms, a 

 good deal is reliably known already, and it predicates the superiority 

 of the converting method in respect of a few metals absolutely, and in 

 respect of certain others relatively, owing to their more expeditious 

 elimination. ]STotwithstan<ling numerous calcinations and oxidising 

 smeltings, the older, less energetic processes admitted of but a mediocre 

 purification from step to step. Arsenic and antimony were practically 

 dragged through the whole curriculum, up to the last. But in the 

 modern practice, even when previous treatment does not essentially 

 work off the injurious elements, the accentuated thermal and chemical 

 vigor of the pneumatic process accomplish a trenchant disruption of 

 affinities in a single operation lasting merely as many hours as the older 

 work took days, weeks, or months. As in the older treatment, purification 

 Is efiected only through two channels, i.e., either by volatihsation or 

 by scorification. But, imder the new conditions, elements and com- 

 pounds become volatile which were less so under the old. Elements 



