wisdom in the choice of a title for their paper. It was one thing to lay out pumping-plant for an entirely new colliery, but it was quite another thing to instal suitable pumping-plant at an old colliery, and one must be content with what seemed best, all things being considered.

He (Mr. Martin) was inclined to disagree with the statement that underground direct-acting steam-engines had little to recommend them except low first cost. For depths of 1,200 or 1,400 feet, where the pumping must be done in the coal-drawing shaft, and steam was already conveyed down the mine for other purposes, perhaps the most satisfactory pump that could be installed was of the direct-acting compound type. It had few wearing surfaces and consequently cost little for stores, very little in the way of repairs, and required a minimum amount of attention. Where there was any movement of the floor, the direct-acting type had a distinct advantage over the rotative engine.

There were serious objections to placing heavy pumping sets in a working-shaft. In laying out a pumping-shaft at a new colliery or a central pumping-plant for a group of collieries, down to, say, 1,200 feet deep, undoubtedly the wisest plan was that of pumping by means of rods driven by a steam-engine placed close to the source of heat, and running on a high grade of expansion, and always taking the precaution of placing liftingsets in the pit-bottom. A direct-acting condensing engine, with a long stroke and steam-jacketted cylinders, would probably give the best results.

The objection raised to the use of single clacks, with multiple beats, was not very obvious, as they worked well, and cost very little for up-keep. The danger arising from shocks could be readily averted by the use of relief-valves.

For dealing with large quantities of water from depths of 1,500 to 3,000 feet, the hydraulic system mentioned in the paper had much to recommend it. The engine on the surface could be made an economical engine, and the hydraulic motor in the mine was also highly efficient. But with this system of pumping, no fewer than four ranges of pipes were necessary, namely: Rising main, power-pipe, return-pipe and air-pressure pipe, but as these were small in diameter, they could be easily fixed in a working-shaft. The cost of this plant must of necessity

be high when the enormous pressures were considered (up to 3,000 pounds per square inch) and they could only be satisfactorily controlled by a liberal use of cast steel in the manufacture of the plant.

The writers of the paper had done well in calling attention to the need of having some uniform method of expressing pumpefficiencies. German engineers, for instance, made statements of extraordinary efficiencies in setting forth the merits of their pumps, but on enquiry the basis of calculation was found not to be the same as that used in this country.

Mr. J. J. PREST (Castle Eden) wrote that the authors were no doubt correct in advocating the more general use of directacting triple-expansion condensing pumping-engines as a permanent installation for dealing with large volumes of water from shafts of a depth of, say, 1,000 feet. The only serious objection to the more general adoption of this class of pumpingmachinery is the amount of room taken up in the shaft by the pump-work together with the first cost of the installation. The problem to be solved in all cases is, whether the economy capable of being effected by the adoption of this class of pumping-engine is sufficient to return ample interest on the increased capitalexpenditure required, as compared with an underground steam pumping-engine, all other things being equal. There can

be no doubt that at least one-half of the fuel is wasted, by condensation, in steam-pipes conveying steam to many large underground pumping-engines. If the value of this fuel so wasted amounts to, say, £500 per annum in the case of a steam underground pump, and the increased cost of a high-class pumping-engine plant should amount to £3,000 only when compared with the underground pumping-engine, then there is sufficient margin to warrant the increased expenditure being incurred. In many cases, however, the economy resulting from the increased capital-expenditure necessary to replace existing plants would not warrant the conversion. For unwatering sinking shafts, the class of pumping-engines advocated by the authors was not suitable.

Mr. A. H. MEYSEY-THOMPSON (Leeds), replying to the discussion, said that none of the results given in the paper were their own figures. Lancashire boilers were used at both the

292

DISCUSSION-THE CHOICE OF PUMPING MACHINERY.

Bradley and Moat pumping-engines, and it was purely accidental that the cost of repairs at one place had been 4s. 10d. and at the other only 1s. 9d. per horsepower per annum. Possibly the feed-water had something to do with it, as the boilers were placed several miles apart. He believed that the Riedler pump, with mechanically worked valves, was not largely in use in this country, although one had been working at the Powell Duffryn collieries for many years. The present electric pump was geared, and gearing was noisy and wasted a lot of power as friction. If a pump could be run at 100 revolutions per minute, with the motor directly connected, it would prove a most useful form of machine. He could not give any definite opinion with regard to the sparking of electric motors: he was told by mining-engineers that violent sparking was dangerous, and when a cable broke there was danger of sparking.

Mr. H. LUPTON (Leeds) stated that the electric plant referred to in the paper from which the figures were quoted, was driven by a compound engine, with cylinders 18 and 30 inches respectively in diameter by 40 inches stroke, running at 80 revolutions per minute and supplied with steam at a pressure of 100 pounds per square inch. It worked two sets of threethrow pumps in the shaft; the actual horsepower in water lifted by the pumps was 121, and the duty of the whole plant was 29,000,000 foot-pounds. The average duty of the engines referred to in the paper was 51,000,000 foot-pounds for steam and 30,000,000 for electricity, where both plants were giving their ordinary duty.

Mr. J. G. WEEKS (Bedlington) remarked that the use of compressed air had been totally ignored throughout the discussion, but there were circumstances under which its use was highly advantageous. He moved that a vote of thanks be accorded. to the writers for their interesting paper.

Mr. J. H. MERIVALE seconded the resolution, which was cordially approved.

The further discussion was adjourned.

Mr. MARK FORD read the following paper on "Sinking by the Freezing Method at Washington, County Durham":

SINKING BY THE FREEZING METHOD AT WASHINGTON, COUNTY DURHAM.

BY MARK FORD.

1. Introduction.-The great interest shown by the members in the operation at Washington, and the novelty of the method, probably adopted for the first time in Great Britain, has induced the writer to give the following detailed description of sinking through alluvial deposits to the stone-head at the Glebe Winning belonging to the Washington Coal Company, Limited.

The company, having acquired the royalties of the Oxclose and Glebe collieries, abandoned forty years ago, decided to sink two shafts, 14 feet and 12 feet in diameter respectively, in a position such as to secure the most economical arrangement of haulage, shaft-bottom and surface-plant in preference to reopening the old shafts.

2. Nature of Ground. After trial-borings had been made over a certain area, it was found that the shafts would be sunk through drift, consisting of sand and boulder-clay. At the site adopted for the shafts, the following section was proved:

3. Method of Sinking. The thickness of the sand-bed, the treacherous character of the quicksand, and the possibility of damaging the foundations of engines, boilers and other erections in the vicinity of the shafts, led, after careful consideration,

20

VOL. XXIV.-1902-1908.

to negotiations with Messrs. Gebhardt & Koenig, Nordhausen, Germany, who undertook to freeze two shafts to the stone-head. This method offered almost a certainty of success, a dry shaft. to sink, and no water or sand to pump to the surface.

4. Preparatory Work. The usual headgear and pulley were erected, and a permanent hauling-engine was so placed that both shafts would be served by it during the sinking (Fig. 5). This engine has two cylinders, each 18 inches in diameter by 36 inches stroke, and is geared as 2 to 1, to two drums, 6 feet in diameter. A locked-coil wire-rope is used for winding.

The first and winding shaft will have a finished diameter of 14 feet. Its diameter to a depth of 24 feet was 24 feet, the sides being secured by ordinary wooden cribs, 6 inches square, placed 3 feet apart, and short backing deals were placed behind the cribs.

At 16 feet from the surface, a scaffold was erected, and on this scaffold, the holes in which the freezing-tubes, 22 in number, had to be placed, were marked off (Figs. 1 and 2, Plate VII.). This was done by drawing a circle on the scaffold having a radius. of 10 feet, and the circumference of this circle was divided into 22 equal parts, giving the centre of each bore-hole.

Boring-tubes were forced down to form the holes through