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Sir Frederick metallic state and had been fused; in other words, what was the Bramwell. ordinary melting-point of nickel?

Dr. Mond.

Prof. Roberts-
Austen.

Dr. LUDWIG MOND pointed out that one of the advantages of the process was that the sulphur need not be completely roasted from the matte in the first instance. The matte was roasted three times, and the sulphur left in at the first calcination was removed by the subsequent ones. There was the very peculiar fact that by attacking the roasted matte with sulphuric acid only a certain amount of copper was dissolved, until a definite relation between nickel and copper was established; still, he did not venture to base any theory on this fact. With regard to the questions asked as to the cost, he might say that he had not come to the Institution to transact business, but if any gentlemen were anxious to know any details about that matter he should be very pleased to reply, if they would send their questions in writing.

Professor ROBERTS-AUSTEN, in reply to the discussion, stated the melting-point of nickel was 1600° C. He had considered the question of cost with very great care, but he felt it was rather beyond him; he was satisfied, however, that the process would compete favourably with any now in use, and he thought it unfair to draw up an estimate as to cost from appliances which were confessedly in a transitionary state. That was the reason why he did not produce the thoroughly comprehensive figures which were submitted to him, not only by Dr. Mond, but by Dr. Langer. He might add that Dr. Stansfield examined these data with the greatest possible care. It was with much confidence that he expressed his belief in the economy with which the process could be conducted.

Mr. Gibb.

Correspondence.

Mr. THOMAS GIBB, of Liverpool, pointed out that keeping all the appliances for the treatment and circulation of the materials and gases rigidly enclosed would entail much skill in the construction and care in the working of the apparatus; this was made comparatively easy by the extremely low temperatures at which the operations were conducted compared with the temperatures usually employed in metallurgy. The Author could not have done a better service to metallurgy than bring before the Institution this unique process, now that its initial difficulties had been patiently and, to all appearance, successfully combated, and it was likely to be launched as an important industrial operation.

The process, worked on a large scale, involved a large production Mr. Gibb. of sulphate of copper. For instance, the 1,000-ton plant contemplated would have to be accompanied by plant for the production of 4,500 tons of crystallized sulphate of copper, and any general adoption of the process would entail a formidable competition with existing works. The copper could be precipitated either by iron or electrolysis; but, however it was performed, the plant for, and cost of, its utilization would have to be reckoned with whenever its quantity became too large to be advantageously placed on the market as sulphate.

15 November, 1898.

WILLIAM HENRY PREECE, C.B., F.R.S., President,

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in the Chair.

(Paper No. 3079.)

Electrical Transmission of Power in Mining."

By WILLIAM BEEDIE ESSON, M. Inst. C.E.

In mining undertakings the disadvantages attendant on expensive transport have recently been to a large extent neutralized by electrical transmission of power. Auriferous quartz is frequently found in regions difficult of access, where the transport of fuel to the mine for the purpose of crushing by steam-power, or conveying the ore to a distant steam- or water-driven mill, would be extremely costly. But these natural disadvantages can be greatly mitigated by the delivery, at the mine, of power transmitted electrically from a distance; and, thus provided, a district traversed by low-grade ore can be made to yield results which, apart from such supply of power, could only be realized if the ore were of rich quality. In several districts the advantages of employing electricity appear to have been completely overlooked, and many properties might have become remunerative at a much earlier date if the benefits which the use of electricity confers had been recognized. There is often abundant waterpower, but mills have been built at the river sides, and, in consequence, the great cost of transporting the quartz to the mills has prevented profitable working. By using electrically transmitted power, the mills might have been built at the mines and the rock crushed there, with great saving of expense and certain profit.

The Author does not propose to institute a comparison between electrical and other methods of transmitting power. The matter may be dismissed with the observation that, so far as the

application of power-transmission to mining work is concerned, electricity is generally the only practicable means. The ease with which copper wire can be carried over any kind of country, wherever desired, coupled with the plastic character of the material, renders the electrical conductor the simplest and most reliable of all vehicles for power-transmission; while the induction electric motor is of all machines the least complicated, and, on account of its simplicity of construction, the least likely to suffer serious injury or damage through rough usage. Motors of this kind are adapted for driving stamps, crushers, haulinggear, pumps, fans, and all the other machinery connected with mining.

As a general rule, before deciding whether power-transmission shall be adopted, it is only necessary to compare the cost of two schemes (a) bringing fuel to a mine to work the machinery by steam; (b) transmitting power to a mine electrically from a generating-station situated at some convenient position for utilizing existing water-power. The working expenses added to the interest on the capital invested make up in both cases the annual cost, but it must not be forgotten that the number of hours worked per day constitutes an important factor. The first cost for either scheme depends on the maximum power to be transmitted, and is independent of the hours of working, but it is not so as regards the working expenses. While the cost of water may be merely nominal, fuel must be paid for in some way; and while a comparison of the schemes might show for 12 hours working per day a result in favour of steam, for a 24-hour day the evidence might be largely in favour of water.

The foregoing applies to the usual circumstances under which the choice lies between laying down steam-power at the mine, and electrical transmission to the mine, of power derived from water; but there are cases in which electrically transmitted power with the generators driven by steam may have a good chance of success. The Rand Central Electric Works afford an example of the latter class of installation. The generators are driven by large steamengines at the mouth of the Brakpan coal-pits, where fuel can be easily obtained at a comparatively low price, the power being transmitted for about 30 miles to mines difficult of access for ordinary delivery of fuel. The cost and difficulty of constantly transporting fuel makes the working-expenses very high, and it is estimated that the average cost to mine owners on the Rand of one steam horse-power per annum is £56 108., taking large and small engines together, and excluding interest and depreciation. It is reckoned

that the total steam-power on the Rand is 21,000 HP., and the Company whose works are referred to has, as a first instalment, laid down plant for transmitting 2,100 brake HP., charging mine owners at the rate of £45 per brake HP. per annum. A general power-delivery scheme of this kind has many advantages over independent steam-plants at individual mines, and several such projects are at present under consideration.

The electrical transmission plant now to be described has been in continuous work at the Sheba Company's mines, Barberton, Transvaal, for more than 2 years; and, though previous to its being started, electricity had played a not unimportant part, so far as supplying power from steam-driven generators for pumping, hauling, &c., was concerned, there had been no attempt to substitute for the steam-power required for working the heavy machinery, the power of water transmitted from a distance. For what electrical work there was, continuous current machinery was used, whereas the Sheba installation, about to be described, is worked by alternating currents.

The Sheba Mine is situated in the mountainous district of the De Kaap Goldfields, Fig. 1, Plate 2. The first mill was built on Fig-Tree Creek, on a site 3 miles from the mine. It consisted of twenty stamps, and the power was derived partially from the water in the creek and partially from steam generated by wood fuel. The ore was transported from the mine to the mill by ox-wagons. The second mill, a fine battery of sixty stamps, was erected on the Queen's River, and was driven by turbines. The rock was conveyed to the mill by an aerial ropeway, about 2 miles long, over the mountains. The ropes were carried on high standards, and long spans were demanded by the conditions of the country. After much trouble and expense this ropeway was brought into excellent working order, but an enormous flood in February, 1895, washed away the dam and the water-race; the mill had to be closed, and there was no further use for the aerial ropeway.

At the date of the flood referred to, a new mill of sixty stamps was being erected upon a site selected as near to the mine as local conditions would allow; and a power-house was being built on the Queen's River at Avoca, 5 miles from the mine, to carry out the electrical transmission scheme. The original plans embraced the supply of power to drive the battery with the vanners, crushers and pumps, and to light the mine. This was to be an experimental plant, and on its success depended further extensions. It had been estimated from gaugings of the river

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