HISTORICAL SKETCH
The ores of the base metals when taken from the earth contain the valuable portion in chemical combination, generally with sulphur, in the form of particles of metallic sulphide, mixed with a large quantity of worthless rock. The ore is first crushed to a suitable degree of fineness, in order to free the sulphide particles from the adhering gangue, and the crushed mass is then subjected to mechanical operations with a view to separating all the sulphide particles into one pile, and all the worthless gangue into another pile. The sulphides are then smelted to recover the metals. The oldest method of accomplishing this separation is by mixing the crushed ore with sufficient water to form a freely-flowing pulp and then subjecting the pulp to a shaking, throwing, and flowing motion, on suitable machines, whereby the sulphide particles, being much heavier than the gangue, travel faster and farther than the gangue, and are diverted at the proper time and place to effect a separation. This method is ancient, and was the only one known for hundreds of years.
A second method, introduced not long ago, made use of the magnetic qualities of the valuable minerals. These in general have a stronger magnetic permeability than the gangue, and if the ore is suitably subjected to the influence of powerful magnets, the valuable mineral particles can thereby be separated from the worthless gangue.
These two methods have limitations as to their usefulness, and these limitations have been a constant spur to metallurgists, urging them to the discovery of new modes of treatment.
The knowledge that substances heavier than water would, under suitable conditions, float on its surface is not at all new, the best known example being that of a greased needle carefully placed on water. It has been known also for many years that some heavy substances will float on the surface of water with more certainty than others, and the principles involved in this fact formed the basis of a third method of separating mineral sulphides from gangue as soon as it was recognized that the sulphides would float with greater facility than the gangue. The successful concentration of ores by causing the metallic sulphides to float at the surface of a liquid, and the gangue or waste rock to sink within, with entire disregard of relative specific gravities or magnetic qualities, has now not only overcome the suspicious novelty of its earlier phases, but has an established and growing position in the metallurgy of the base metals. The progress of the practical application of this principle has been so great during the past ten years as to place it now among the sure expedients of the metallurgist. To the minds of those who have had occasion to apply the process it seems almost as great an advance in the dressing of base-metal ores as the cyanide process proved to be in the recovery of the precious metals. In the recovery of zinc sulphides, especially from the by-products of lead milling, and also of finely disseminated copper sulphides from silicious gangues, it has already a wide field in instances where other methods were of imperfect application, and the range of its application is daily being widened.
A new metallurgical process never springs fully developed from the brain of one person, but is the result of patient investigation, application, and improvement by many minds, during many years. Metallurgical advances can best be likened to the construction of a pyramid by the constant addition of material.
The erection of such structures can never be credited to a single person. The first stones are usually laid by those who had an imperfect vision of the structure that would arise, and while many builders come into prominence from year to year, many stones are laid by unknown hands. No builder need flatter himself he has completed the structure by placing a peak stone in place, for while he is in the very act, it is quite likely an ambitious newcomer has begun a dozen new courses of masonry at the base of the pyramid. Unfortunately, besides the question of individual credit, there also enters the more serious one of ownership to parts of the structure. Constructive work may be entirely suspended while the courts adjudicate the rights of rival claimants ; the completion of the structure is delayed ; the time and means of the builders are wasted ; and the needs of the industry suffer. The names of those who are known to have helped in this case are Haynes, Tunbridge, Miss Everson, Hebron, Bradford, Dode, Sutton, Robson, Crowder, the Elmore brothers, Potter, Delprat, Van Meter, Boss, Haultain, Stovel, Froment, Scammell, Cattermole, Goyder, Laughton, Wolf, Sulman, Picard, Ballot, De Bavay, Darling, Gillies, Kirby, Macquisten, Sanders, Schwarz, Chapman, Kendall, Latimer, Hoover, Norris, Higgins, Lockwood, Samuel, Greenway, Horwood, Wentworth, Lavers, Nutter, Hyde, Hockley, Rouse, Maleczek, Allen, Wynne, Dick, Ruthenburg, McCourt, Orr, and Good.
Tardy justice demands that among those who builded better than they knew, the name of Carrie J . Everson, an American schoolteacher, and an assayer and chemist of ability, should be specially mentioned, because she discovered and enunciated the main and fundamental principles upon which all subsequent work has been based.
The development of this important department of metallurgy can be divided roughly into three stages. During the first of these, 1860 to 1902, there were brought forward at least a dozen methods for causing sulphides to float on an ore-pulp, and these methods fell into two principal classes, although there were even then some patents which could not properly be placed in either class :
(1). Those depending on the selective action of oily substances for sulphide particles to entrap the sulphides, and the buoyancy of the oily substance to effect flotation.
(2). Those depending on the selective action of gas for sulphide particles, and which under certain conditions endowed the particles with a gaseous envelope, and so induced flotation.
Neither of these ideas when used independently produced entirely satisfactory results, although they were not without some commercial profit.
The second stage, from 1902 to 1907, was marked by a practical advance when the idea was developed of endowing the particles with an oily coating in an acid solution, thus increasing their affinity for the gaseous envelope. This combination of the two fundamental ideas of the preliminary stage has made it possible to secure a high degree of flotation among many sulphides. These two stages belong primarily to the inventor, the so-called unpractical man.
The third stage, 1907 to 1912, in which we now are, is the stage of the engineer : the commercial application of the idea. Suitable mechanical devices had to be invented to produce the proper mixture of gases, liquids, and solids, and to entrap the concentrate when afloat. This stage has now reached so practical a development as to find widespread commercial application.
The different processes have been developed along several lines parallel to each other, so that it is difficult to discuss them as a whole chronologically. They will, therefore, be considered separately in the order of their first appearance.
