TRANSACTIONS OF SECTION B. 593 



soluble sulpbate of silver. If arsenic and antimony have not been eliminated, their 

 presence at the end of the operation will be specially inconvenient, as they 

 give rise to the formation of arseniate and antimoniate of silver, insoluble in 

 water, which may necessitate the treatment of the residues by an entirely different 

 process from that which has hitherto been considered. 



It will have been evident that effecting this series of changes demands the 

 exercise of the utmost skill, care, and patience. The operations beginning at a 

 dull red heat, or a temperature of some 500°, are completed at 700°, within a 

 range, that is, of 200°. Judicious stirring has been necessary to prevent the 

 formation of crusts of sulphates, which would impede the reactions, and, as has 

 been shown, an undue elevation of temperature within a very limited range would, 

 at any stage, have been fatal to the success of the operation. It is difficult to 

 appreciate too highly the delicacy of sight and touch which enables an operator to 

 judge by the aid of rough tests, but mainly from the tint of the streak revealed 

 when tiie mass is rabbled, whether any particular stage has or has not been 

 reached, and it will be obvious that the requisite skill is acquired solely by obser- 

 vation and experiment. The technical instructor may impart information as to 

 the routine to be followed, and the appearances to be observed, but scientific 

 knowledge of a high order can alone enable the operator to contend with the 

 disturbing influences introduced by the presence of unexpected elements or by 

 untoward variations in temperature. In the training of a metallurgist it is 

 impossible to separate education from instruction, and the above description of a 

 very ordinary operation will show the intimate relations between science and 

 practice which are characteristic of metallurgical operations. Practice is depen- 

 dent on science for its advancement, but scientific workers too often hesitate to 

 attack metallurgical problems, and to devote the resources of modern investiga- 

 tion to their solution, because they are not aware of the great interest of the 

 physical and chemical problems which are connected with many very simple 

 metallurgical processes, especially with those that are conducted at high tem- 

 peratures. 



Proceeding yet one step further, suppose that the copper smelter takes posses- 

 sion of the residual mass, consisting mainly of oxide of copper, he would smelt it 

 with fresh sulphide ores and obtain, as a slag from the earthy matters of the ore, 

 a ferrous silicate containing some small proportion of copper. The displacement 

 of the copper from this silicate may be effected by fusing it with sulphide of iron, 

 a fusible sulphide of iron and copper being formed which readily separates from 

 the slag. By this reaction some twenty thousand tons of copper are added to the 

 world's annual production. Proceeding a step further, suppose the smelter to have 

 reduced his copper to the metallic state. If arsenic had been originally present in 

 the ore, and had not been eliminated entirely in the roasting, extraordinary diffi- 

 culties would be met with in the later stages of the process, in extracting small 

 quantities of arsenic which resist the smelter's efforts. Copper, moreover, con- 

 taining above one per cent, of arsenic cannot be ' overpoled,' as the presence of arsenic 

 hinders the action of gases on the copper. The amount of arsenic which the copper 

 smelter has to remove may vary from mere traces up to one per cent., and if the 

 copper is destined for the use of the electrical engineer, he will insist on its being 

 as pure as possible, for the presence of a trace of arsenic would materially increase 

 the electrical resistance of the copper, and would be fatal to its use in submarine 

 telegraphy. If, on the other hand, the copper is intended for the maker of locomo- 

 tive fire-boxes, he will encourage the retention of small quantities of arsenic, as 

 it is found to actually increase the endurance of the copper, and the smelter will 

 in such a case have no inducement to employ the basic furnace lining which Mr. 

 Gilchrist has offered him, nor will he care to use the special methods for the 

 removal of arsenic with which he is familiar. It may all seem simple enough, 

 but the modern process of copper smelting has been laboriously built up, and has a 

 long and interesting pedigree which may be traced to at least the eighth century, 

 when Geber described the regulus ' coarse metal ' as being ' black mixed with 

 livid,' and our famihar 'blue metal ' as being ' of a most clean and pleasant violet 

 colour,' and indicated the reason for the difference. 



1891. QQ 



