TRANSACTIONS OF SECTION B. 591 



does not come within the ordiuaiy sphere of the academic teaching; of chemistry. 

 It is often urj^ed that metalhirrjical practice depends upon the application of 

 chemical principles which are well taught in every large centre of instruction in 

 this country, but a long series of chemical reactions exist which are of vital 

 importance to the metallurgist, though they are not set forth in any British manual 

 of chemistry, nor are dealt with in courses of purely chemical lectures. I feel 

 bound to insist upon this point, because, as Examiner in Metallurgy for the Science 

 and Art Department, I find that purely analytical and laboratory methods are so 

 often given in the belief that they are applicable to processes conducted on a large 

 scale and at high temperatures. 



We are told that technical instruction should be kept apart from scientific 

 education, which consists in preparing the student to apply the results of past 

 experience in dealing with entirely new sets of conditions, but it can be shown 

 that there is a whole side of metallurgical teaching which is truly educational, and 

 leads students to acquire the habit of scientific thought as surely as the investiga- 

 tion of any other branch of knowledge. 



It is, in fact, hardly possible in a course of theoretical chemistry to devote 

 much attention to specific cases of industrial practice in which reactions are incom- 

 plete, because they are limited by the presence of bodies that cannot be directly 

 eliminated from the chemical system. Take, for instance, the long series of re- 

 actions studied by Plattner, who published the results of his investigations in his 

 celebrated treatise, * Die Metallurgische Rostprozesse,' Freiberg, 1856, whose work 

 I have chosen as a starting-point on account of our presence iu South Wales near 

 the great copper smelting district of Swansea. A complex sulphide, of which 

 copper is the main metallic constituent, contains some fifty ounces of silver to the 

 ton. The problem may be supposed for the present to be limited to the extraction 

 of the precious metal from the mass in which it is hidden, and the student deriving 

 his knowledge from an excellent modern chemical treatise "vvould find the case 

 thus stated : — 



' Ziervogel's process depends upon the fact that when argentiferous copper pyrites 

 is roasted, the copper and iron sulphides are converted into insoluble oxides, whilst 

 the silver is converted into a soluble sulphate which is dissolved out by lixiviating 

 the roasted ore with hot water, the silver being readily precipitated from this solution 



in the metallic state.' 



f 



It is certain that if an observant, chemically-trained student visited a silver 

 extraction works, and possessed sufficient analytical skill to enable him to secure 

 evidence as to the changes that occur, he would find a set of facts which his train- 

 ing had not enabled him to predict, and he would establish the existence of a set of 

 reactions to the nature of which his chemical reading had hardly given him a clue. 

 The process to be considered is a simple one, but it is typical, and applies to a 

 large proportion of the 7,000,000 ounces of silver annually obtained in the world 

 from cupriferous compounds. He would be confronted with a ton or more of 

 finely divided material spread in a thin layer over the bed of a reverberatory fur- 

 nace. Suppose the material is what is known as a complex regulus as imported 

 into Swansea or produced at Freiberg, to which are added rich native sulphides. 

 The mixture then consists of sulphides mainly of iron and copper, with some sulphide 

 of lead, and contains fifty or sixty ounces of silver to the ton, and a few grains 

 of gold. It may also contain small quantities of arsenic and antimony as arsenides, 

 antimonides, and sulpho-salts, usually with copper as a base. 



The temperature of the furnace in which the operation is to be performed is 

 gradually raised, the atmosphere being an oxidising one. The first effect of the 

 elevation of the temperature is to distil oif sulphur, reducing the sulphides to a 

 lower stage of sulphurisation. This sulphur burns in the furnace atmosphere to 

 sulphurous anhydride (SO.,), and coming in contact with the material undergoing 

 oxidation is converted into sulphuric anhydride C^Og). It should be noted that 

 the material of the brickwork does not intervene in the reactions, except by its 

 presence as a hot porous mass, but its influence is, nevertheless, considerable. The 

 roasting of these sulphides presents a good case for the study ef chemieal equili- 



