The CHAIRMAN, in moving the adoption of the Annual Report of the Council and of the Finance Committee, commented upon the financial results of the year, and said that those who could inculcate the idea of prompt payment of subscriptions among the members and who would adopt the same themselves would relieve the Institute of a great deal of trouble in the secretarial department and keep them, as they ought to be, well up in funds. The Council hoped that another year would find them in a much better financial condition, but this, however, would depend on the number of members being maintained. No doubt, as the report said, in referring to the 971 members in 1877, there were causes to account for the loss of members since then; one reason was the great competition in regard to the mechanical engineering element by kindred institutions. The establishment of the North-East Coast Institution of Engineers and Shipbuilders had taken a large number of those members who were purely mechanical engineers and not interested in mining subjects. But it must be remembered that, being the parent Institute of the Federated Institution which they had joined, and which gave them the advantage of having the papers of all the other districts embodiel in the Transactions (so that they were not dependent on them. selves altogether for papers on mining matters), it must not be otherwise written of them than that they felt the greatest responsibility on themselves to keep the foremost in all they did and the papers they read, so as not to lose that preeminence which, he maintained, they had held to the present time, and which, in becoming amalgamated with the Federated Institution, it behoved them to strain every nerve to maintain. He thought there was only one other matter on which he might say a word or two, and that was as to the desirability of better attendances at the general meetings. There was an enormous amount of good work done by committees silent work, the results of which they could only see when it was printed in the Transactions; work done in committees was no doubt better than that done in ordinary meetings in delivering one's self of set speeches, but from the earnestness with which matters were discussed and the benefit that was got from knocking their opinions against each other, in public meetings they should feel that the attendances were not as satisfactory as they should be, and it behoved the Council to enquire whether the menu was good enough. He had known the history of this Institute for thirty-four years and certainly the attendances formerly were very much larger than now. He hoped that in the reign of his successor they would inaugurate something by which to secure larger attendances and that valuable discussions would arise on the papers read. He then moved the adoption of the reports of the Council and of the Finance Committee..

Mr. J. B. SIMPSON seconded the adoption of the reports, which was put to the meeting and carried unanimously.

VOL. 11.-1-90-91.

3 L

REPRESENTATIVES ON THE COUNCIL OF THE FEDERATED

INSTITUTION OF MINING ENGINEERS.

The SECRETARY reported that this Institute was entitled to seventeen representatives on the Council of the Federated Institution, the Chesterfield Institution to seven, the Midland to five, and the South Staffordshire to three. The Council recommended the re-election of the representatives appointed last year, together with Messrs. H. Lawrence and Professor J. H. Merivale, instead of Messrs. John Marley and Jas. Willis, who had died during the year, and of himself, who would attend as their Secretary.

Mr. STRATTON remarked that three names were withdrawn from the list and only two substituted.

The SECRETARY explained that, by the alteration of the rules of the Federated Institution, they were now only entitled to seventeen elected representatives on the Council, instead of the thirteen elected and four co-optated members of Council under the old rules.

The CHAIRMAN-Then, there are two vacancies to-day, and the Council recommend the re-election of the old representatives, together with Mr. Lawrence and Professor Merivale.

This resolution was put to the meeting and unanimously agreed to.

The representatives of the Institute for the ensuing year are as follows:—

W. Armstrong, Esq.
W. Armstrong, Jun., Esq.

Sir Lowthian Bell.
Thos. J. Bewick, Esq.
Robt. F. Boyd, Esq.

M. Walton Brown, Esq.

Wm. Cochrane, Esq.

Jno. Daglish, Esq.

Thos. Douglas, Esq.

G. B. Forster, Esq.

G. C. Greenwell, Esq.
Henry Lawrence, Esq.
Geo. May, Esq.
Prof. Merivale.

J. B. Simpson, Esq.
A. L. Steavenson, Esq.

David Dale, Esq.

Lindsay Wood, Esq.

Mr. COCHRANE read the following paper, "On a Duplex Arrangement of Centri.

fugal Ventilating Machines":

ON A DUPLEX ARRANGEMENT OF CENTRIFUGAL VENTILATING

MACHINES.

BY W. COCHRANE.

In the course of an investigation with the late Mr. J. J. Atkinson, H.M. Inspector of Mines, in 1868, into the working of two Guibal ventilators at the Duffryn Collieries in South Wales, some interesting results were obtained, and a novelty was established in the application of two centrifugal machines, which it seems to the writer may be worthy of imitation under special circumstances. The ventilators, 30 feet diameter, were erected side by side, the two engines, 24 inches diameter and 24 inches stroke, being placed in a house between the ventilators, and a separate drift, but of different sectional area, from the upcast shaft was carried to each of the inlets.

The ventilation of the colliery was represented by about 80,000 cubic feet of air per minute, with a water-gauge of about 1.60 inches at the surface, and each ventilator was capable of producing this at a speed of about 58 revolutions per minute.

If the ventilators were run together at this same speed there was no important variation in volume, but a slight alteration in water-gauge, which was attributed to the different conditions of the two drifts from the upcast shaft.

The water-gauge, as is well known, is dependent on the velocity of the periphery of a centrifugal action ventilator; the only benefit from running two together as compared with one would arise from the lessened resistances encountered by the air in its passage through two surface-drifts and two ventilators at lower speeds than that with which the whole quantity would pass through a single drift and a single ventilator (it would be a very small amount), provided the one drift was of proper sectional area and the blades of sufficient breadth, with the outlet shutter properly adjusted-this small benefit would be discounted by the extra friction due to two engines and ventilators instead of one,

It was not considered safe to put the ventilators up to any higher speed for permanent work in order to obtain the increased ventilation which was required. The suggestion of the late Mr. J. J. Atkinson was to arrange the ventilators to work in duplex or tandem form, so that having expended the work of one, equal to circulating 80,000 cubic feet under 1.60 inches, the other should take up this volume of air at its decreased tension and impart to it a second equal work.

By this arrangement it would be possible to apply double the power through the two engines, and as the quantities of air are proportional to the cube roots of the powers circulating them in the same mine this was estimated to afford

1.26, or 26 per cent. more air at the same speed of the ventilators. The 1262 water-gauge at the surface for this increased volume would be 1002

= 1.5876, or 58.76 per cent. higher than that existing, involving the increased speed of a single ventilator by 26 per cent., if that had been deemed the proper course; but the liability to heating and breakage, arising from high speeds of ventilators of large diameters where continuous working is a necessity, precluded such a recommendation; otherwise the increased speed, and the resulting higher water-gauge and volume of air, would have been obtainable by the single ventilator or the two working together side by side by the expenditure of about the same increased steam power, either in one cylinder or divided between the two.

The whole of the air from the upcast shaft was carried along one drift only to one of the ventilators, and at the foot of the chimney of this ventilator a drift was formed to connect with the inlet of the second ventilator, the air thus passing through the second ventilator and up its chimney into the open atmosphere. Suitable air-tight doors in the two drifts from the upcast, and at the foot of the chimney of the first ventilator were arranged so as to afford full opportunity of experiment.

Preliminary tests had been made with small cupola fans before proceeding to the important expenditure required in the above arrangement. They indicated that the estimated result would agree with the theoretical considerations due to the additional imparting of power by each additional fan, not only in exhausting from a mine, but also in producing accumulated pressure as a forcing fan.

The immediate ventilation required involved a considerably higher water-gauge -nearly double--and therefore, a corresponding increase in the effective pressure of steam in the engine cylinders was necessary. The air to be put in circulation √2 would thus be 1.4142, or 41.42 per cent. increase. Allowing for the VI

=

greater resistances due to the air passing through two ventilators instead of one, it was estimated that one-third larger volume of air would be obtained in practice at the same speed of each ventilator by this duplex arrangement.

To have arrived at a similar result with one ventilator, would have required a speed of 41.42 per cent. higher than that at which it was running.

The works to carry out the suggestion having been executed, the following experiments were made to test the results.

1st. The two ventilators, exhausting on the duplex or tandem system, each making 60 revolutions per minute, yielded 108,479 cubic feet of air under a water-gauge at the inlet of the ventilator nearest to the upcast of 2.80 inches, and near the inlet of the leading ventilator of 1·10 inches. 2nd. The nearest ventilator to upcast, blowing through the leading ventilator (stationary), gave 79,218 cubic feet with a water-gauge at its inlet of 1.10 inches, and near the inlet of the leading ventilator of '80 inches. 3rd. The leading ventilator, drawing through the nearest to upcast (stationary). gave 81,405 cubic feet with a water-gauge of 1·40 inches at the inlet of the latter, and of 1.75 inches near the inlet of the former.

4th. The ventilator nearest to upcast, working with separate drift from upcast and its own chimney, gave 88,798 cubic feet with a water-gauge at its inlet of 1.80 inches.

5th. The front or leading ventilator, with separate drift from upcast and its own chimney, gave 77,133 cubic feet with a water-gauge near its inlet of 2.10 inches.

6th. The two ventilators working simultaneously, having their inlets connected with the double drift from upcast, and each discharging by its own chimney, gave 90,310 cubic feet with a water-gauge of 2.10 inches at the inlet of the ventilator nearest to the upcast and of 2:15 inches near the leading ventilator.

There are some anomalous figures, when closely compared, attributable to the sliding shutters of the evasée chimney not being adjustable, to the difficulties of taking several anemometer observations by different observers underground, and also to the varying sectional areas and directions of the drifts connecting the ventilators with the upcast shaft, and with each other, but taking the first three experiments, it will be seen that the average of 80,312 cubic feet circulated by a single ventilator was increased to 108,479 by the duplex-about 35 per cent. increase.

The indicated horse-power of the engines was 179.65 in the duplex, and 70-20 average for each of the ventilators working alone, showing very nearly the theoretical proportion of the cubes of the volumes of air.

Comparing Nos. 4, 5, and 6 experiments, it is also seen that the single ventilator nearest to upcast alone, at 60 revolutions, gives nearly the same ventilation as the two working simultaneously; the leading ventilator at the same speed of 60 revolutions, probably owing to the increased frictional resistances, being inferior to the other. Had the drifts from the upcast been precisely similarly arranged in reference to each of the similar ventilators the volume of air would have divided itself equally between the two machines working simultaneously, and the horsepower developed by each engine would be theoretically one-half of that which