July 6, 1911] 



NATURE 



while in the lowest rank of the profession. The college 

 course must contemplate the fitting of a student for his 

 whole career, and provide him with an intellectual equip- 

 ment which will only gradually become useful as he rises 

 to higher rank in his profession. The view of the 

 employer who looks only to the immediate usefulness of 

 the student is a short-sighted one. 



Nevertheless, a college course is an unpractical and 

 badly designed one if, at the end of it, a student is not 

 more capable and useful from the first, in any type of 

 workshop, than a lad without such a training. The 

 college discipline is bad if he has not much more character 

 and energy than the raw lad. His training has been a 

 failure if he does not pick up the specialised details of 

 any business to which he may be put far more rapidly 

 than an untrained lad. I should like to suggest to those 

 practical engineers who are implicitly, if not openly, 

 hostile to college training, who w-ould, at any rate, greatly 

 restrict it, and who advocate lengthened periods of work- 

 shop apprenticeship, that they exaggerate the value of such 

 workshop experience as an ordinary apprentice gets. I 

 am not, of course, considering artisan apprentices, but 

 young men expecting to rise to positions of trust. Here 

 and there are works where special trouble is taken with 

 apprentices ; but in general apprentices are left to pick up 

 what knowledge they can with very little help, and in 

 many cases, I think, a good deal of their time is absolutely 

 wasted. Some skill of handicraft is no doubt acquired. 

 But the engineer works with his head, not with his hands, 

 and manual skill is of use to him only in very exceptional 

 cases. 



I hope I do not in any way underrate the value, to 

 mechanical engineers especially, of that kind of know- 

 ledge of materials, of tools, of processes, and of cost which 

 can only be learned in the workshop. But I think prac- 

 tical engineers forget how little of this valuable knowledge 

 really comes to the works apprentice. The engineer of 

 higher rank who discusses matters with foremen and 

 draughtsmen, who has responsibility for design and cost, 

 and is, moreover, in a position to know the reason of all 

 decisions, is learning in the workshop all his life, and 

 naturally sets a high value on the knowledge slowly 

 acquired by years of constant and close observation. So 

 high a value that perhaps he ignores the importance of 

 the scientific knowledge which was, somew-here and by 

 someone, applied in bringing his business to a state in 

 which it can be carried on successfully as a mere manu- 

 facture. But the knowledge which comes to those in 

 responsible positions is not open to the ordinary appren- 

 tice, and he learns slowly, if at all, unless he brings to 

 the works such a knowledge of principles and methods 

 that he can interpret for himself what he sees. No svstem 

 of workshop apprenticeship can, I think, be considered 

 satisfactory unless someone is specially charged with care 

 of the apprentices, whose duty it should be to make sure 

 that they have opportunity of seeing a great variety of 

 work and of helping them over their difficulties. 



I believe employers will find — some of them have found 

 already — that they owe a debt to the colleges, and that the 

 college-trained student will prove, with a minimum of 

 special experience, a valuable assistant, and in some cases 

 the originator of a real advance in practice. I should 

 like to plead that in return the employer might be a little 

 more ready to give college students a year or two years' 

 run of the works, either without remuneration or with a 

 small remuneration just enough for disciplinary purposes. 

 I do not think there would be any loss in the case of a 

 properlv trained student, and the employer would in many 

 cases find an assistant worth keeping and promoting. 



GOLD MINING IX THE TRANSVAAL.' 

 ""FHE discovery of gold on the Witwatersrand was made 

 in the year 1SS5. The growth of the field was at 

 first slow. Some of the earliest workers believed that the 

 auriferous gravel, exposed in shallow open workings, was 

 a superficial deposit of the nature of the alluvial " placers " 

 of California and Australia. The true character of the 



1 Al.-i.lged from the nineteenth "Tames Forrest" lecture delivered on 

 Tnne 2S before the Institution of Civil Enaineers by Dr. F, H. Hatch, vice- 

 president of the Institution of Mining anil Metallurgy. 



no. 2175, vol. 8;] 



conglomerate beds was, however, soon, realised by those 

 who were fortunate enough to possess some geological 

 knowledge, and by 1SS7 stamp-mills were in operation, the 

 output from the Witwatersrand mines for that year being 

 81,045/. From 1SS7 onward the progress has been rapid. 



Down to the permanent water-level, at a vertical depth 

 varying from 200 to 300 feet, the conglomerate beds were 

 " free-milling," that is to say, the iron pyrites, with which 

 the gold is intimately associated, had been destroyed by 

 oxidation, thus setting free the gold. Below the water- 

 table the colour of the rock changes from red to blue : the 

 ore becomes pyritic ; and the gold is no longer so amenable 

 to recovery by amalgamation, as is the case with the 

 oxidised ore. This was the first difficulty that had to be 

 overcome. Up to the year 1890 the treatment of the Rand 

 ore had consisted of crushing in stamp-mills, and the 

 recovery of 50 to 60 per cent, of the gold, by amalgamation 

 on mercury-coated copper plates. The tailings received no 

 further treatment ; they were considered to be valueless, 

 and, where the ground permitted it, were allowed to flow 

 away. 



The successful introduction of the cyanide process in 

 1890 inaugurated a new era in the history of Rand gold 

 mining. It is no exaggeration to say that the great 

 success of the Witwatersrand gold industry is a direct 

 result of the introduction of the cyanide process. For the 

 majority of the mines, the gold won by this process repre- 

 sents the difference between profit and loss, and without it 

 the profitable working of the vast quantity of low-grade 

 banket now being mined on the Rand would be impossible. 



At first the pulp from the stamp-mills was run into 

 retaining dams, from which the sand was afterwards dug 

 out and conveyed in Scotch carts or in mine-trucks for 

 treatment in the cyanide vats. On account of the slime 1 - 

 content, only 30 per cent, of the gold left in the pulp . 

 from the amalgamating tables was recovered, the re- 

 mainder being in the untreated slimes and in the residues. 



The next step was the introduction of hydraulic 

 classifiers, by means of which a considerable proportion of 

 the slime was eliminated and a sand product obtained, 

 which could be run direct into leaching tanks. 



A process was then evolved for the treatment of the 

 slimes. It consisted in causing the slime, overflowing from 

 the sand-collectors, to settle, by the addition of lime, the 

 bulk of the water being subsequently removed by decanta- 

 tion. The concentrated slime so obtained was then 

 agitated with cyanide solution, which was ultimately drawn 

 off by decantation. 



The separation of sand from, slime by the old-fashioned 

 inverted pyramidal form of hydraulic classifier, and the 

 decantation method for the removal of water or cyanide 

 solution from sand or slime, are now giving place to the 

 use of diaphragm cones and vacuum filters. In the most 

 modern plants the separation of sand and slime in a mill 

 product is effected by feeding the mill-pulp into a cone- 

 shaped collector or diaphragm cone ; the sand is drawn 

 off as a thickened pulp from the bottom, while the slime 

 flows over at the periphery, and after passing through a 

 secondary washing cone is freed from most of its remain 

 ing water on a Caldecott filter-table, which is a slowly 

 rotating horizontal vacuum filter. 



The treatment of slime has been much facilitated by the 

 recent introduction of air-agitation tanks and vacuum- 

 filters, which enable the enriched cyanide solution to be 

 rapidly drawn off from the slime-residue and sent as a clear 

 liquid to the extractor boxes. The precipitation of the gold 

 was effected in the original MacArthur Forrest process by 

 zinc shavings, and this method is still preferred for the 

 rich solutions ; but for weak solutions, such as are obtained 

 in the treatment of slimes, zinc dust is employed as a 

 precipitant. 



One important result of the perfection of the slimes- 

 treatment process has been the introduction of fine grind- 

 ing in tube-mills, with consequent increased extraction and 

 shortened treatment period. Further, the adoption of tube- 

 mills has modified the function of the stamp-mill. Stamps 

 are no longer employed for fine crushing, and amalgama- 

 tion in the mortar-boxes has been completely abolished ; 

 and even such plate-amalgamation as took place in front of 

 the stamp-mills has in many cases been done away with. 

 Concurrentlv with the limitation of the effective range 



