Mr. Herbert, give the same frictional loss, and as Mephan Ferguson pipe could be made rather cheaper per ton than riveted pipe, for equal efficiency as a pressure-main, Ferguson pipe cost about two-thirds the price of riveted pipe. It would be noticed, from the actual tests described on p. 74, that the loss of water through 295 miles of main, including nine pumping-stations and nine large reservoirs, amounted to less than 3 per cent., allowing the full delivery of 5 million gallons per diem: which spoke volumes for the efficiency of the pipes and joints. No figures were given to show the basis on which the diameter of the Coolgardie pipe-line had been determined, and as this was an important matter, it might be interesting to analyse it. From figures given by the Author (which could, of course, have been ascertained approximately when determining the size of pipes required), the cost of the pumping-plant, including spares, erected, was equal to £61.25 per horse-power. The charge for fuel at 328. per ton (Newcastle, N.S.W.), assumed to give 74 millions duty in every-day work = £19.71 per foot of head pumped against per annum at 5 million gallons supply per day; and each foot of head cost £64.44 for pumping-plant. Each 1 inch diameter of pipe cost erected £62,333. The friction through 307 miles of pipes delivering 5 million gallons per day (3,472 gallons per minute) would be

The saving in cost of pipes by reducing from 32 inches to 31 inches would be £62,333; while the loss by extra cost of pumpingplant would be £64.44 × 111 = £7,153 + extra annual cost of fuel = £19.71 × 111 = £2,088, which latter capitalized at 5 per cent., 71⁄2 per cent., or 10 per cent. =£41,760, £31,320, or £20,880 respectively. Thus the saving by reducing from 32 inches to 31 inches would be £62,333, while the loss would be, at 5 per cent. £48,913, at 7 per cent. £38,473, and at 10 per cent. £28,033. Similarly, the saving by reduction from 31 inches to 30 inches would be £62,333, and the loss would be £66,968, £52,578, or £38,188. The saving by reduction from 30 inches to 29 inches would be £62,333, and the loss would be £77,510, £60,850, or £44,200. The saving by reduction from 29 inches to 28 inches would be £62,333, and the

loss would be £98,615, £77,425, or £56,235. Thus for a supply Mr. Herbert. of 5 million gallons, and allowing 5 per cent. interest, the most economical size was 31 inches, at 7 per cent. 29 inches, and at 10 per cent. 28 inches. The rate of interest to be allowed depended on the probable life of the goldfields, and the probable lapse of time before the 5-million-gallon supply was required. From the Author's remarks on p. 53 it appeared that the actual demand up to the present had been somewhat disappointing, and that it would have been well to have allowed, say, 7 per cent., and thus save £62,333 in the cost of the pipe; but otherwise the size adopted appeared to be about the best, allowing as it did about 6 per cent. interest. For a permanent town water-supply in England a 4 per cent. basis might safely be assumed, while for an individual mine or speculative venture 10 per cent. would be better policy. The fact of this, the longest water-main in the world, being of steel, invoked discussion on what had become of late years a much-debated point, namely, the relative life of cast-iron and of wrought-steel or iron pipes. Mr. Herbert's own opinion was that very little corrosion occurred in either cast or wrought pipes when placed in natural ground, generally clay; but that in artificial ground, particularly ashes, slag, or any decomposing material, rapid corrosion took place in both, and generally much more rapidly in cast-iron pipes. In bad ground the life of the pipe was almost entirely dependent on the efficiency of the coating. Tar and asphalt appeared to take a much better hold on wrought pipes, probably because these thin pipes quickly attained the temperature of the bath, even if they were not previously heated, which was sometimes done. He believed that within the next 10 years wrought-steel pipes would supersede cast pipes almost entirely for water and gas-mains, and in many places would be used for sewage.

Mr. RUDOLPH HERING observed that the Paper was of special in- Mr. Hering. terest to American engineers, owing to some similarity between the meteorological conditions of the territory near Coolgardie and those of the Pacific coast of the United States. The rainfall in California varied between 3 inches and 42 inches in one year. The prices paid for water near Coolgardie, even at the lowest figure, 258. per thousand gallons, were much higher than the prices paid on the Pacific coast, due partly to the apparently greater difficulties of construction, and partly to the more elaborate structures than were customary in the pioneer works of California. The Coolgardie scheme appeared to be a thorough and efficient solution of the problem, and the work contained a number of suggestions as to [THE INST. C.E. VOL. CLXII.]

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Mr. Hering. details which might profitably be adopted elsewhere. It was not often that 5,000,000 gallons of water must be elevated daily to a point over 1,000 feet higher than, and over 350 miles from, the source, requiring a total dynamic lift at the pumping-station of about 1,700 feet. In this respect the work appeared to be unique. Although practically all the materials for construction had been imported, the work had required less than 5 years to build, which under the circumstances did not seem excessive for its magnitude and the difficulties of the situation. The rainfall-records, as had been the case in California when that State was first developed, were meagre, and much depended on good reasoning. In arid regions the ratio of yield to rainfall varied greatly, being large for large precipitations and small for small ones. In California, with rainfalls less than 10 inches per annum, unless some of the rain fell as sudden showers, there was usually no off-flow at all. San Francisco was obliged for that reason to store its water for 2 and even 3 years. A few years ago the evaporation during 1 year from the storage-reservoirs was greater than the rainfall or the inflow from the catchment-area. In the western deserts of the United States, that portion of the rainfall which did not evaporate percolated to a considerable depth, and continuously fed the rivers, which, like the Colorado River, discharged large quantities of water through the year, although flowing in the midst of a desert. Naturally, such conditions had invited irrigation schemes, which, near the mouth of such a river, would allow the entire flow to be diverted without infringing upon riparian rights. With regard to the quality of the Coolgardie water, the difficulties due to common salt would gradually disappear, particularly if flat and swampy areas on the catchment-area were sub-drained so as to prevent the capillary action near the surface in dry weather from raising the dissolved salts and holding them upon the surface by subsequent evaporation until they were again dissolved by the rain-water. He could not understand how there could be anaerobic bacterial action in the pipes carrying potable water, which should contain a large amount of oxygen. The descriptions of the lockingbar pipe and of the caulking machinery, which seemed to present novelties of value, were of much interest.

Mr. H. C. Hill.

Mr. HENRY C. HILL, of Philadelphia, communicated an account of the reservoir at the Belmont filtering-station, forming part of the works for the improvement, extension and filtration of the water-supply for the City of Philadelphia. This station was situated about 1 mile west of the Schuylkill River, and consisted of a settling-reservoir, eighteen covered -acre filters, and

a covered clear-water basin. The settling-reservoir was divided Mr. H. C. Hill, by an embankment into two compartments, having an aggregate capacity, with 25 feet depth of water, of 72 million gallons. The reservoir was situated on a hillside, mainly in excavation. The area of the east division at the flow-line was 5.4 acres, that of the west division being 5.33 acres. The east division was constructed about equally of cut and fill, while the west division was nearly all in excavation, principally a quartz-like trap rock with some micaceous rock. In making embankments the most impervious materials of excavation were placed next the inner slope, and all materials were rolled in layers not exceeding 6 inches in thickness. Whenever excavation in rock revealed fissures, these were filled with Portland-cement grout, and the irregular surfaces of the rock in the floors and slopes were levelled up partly with clay puddle, and partly with Portland-cement concrete. In preparing the foundation for the rolled embankment all top soil was thoroughly stripped off, and the inclined ground was stepped in horizontal terraces. All embankments and fills were rolled with four 25-HP. traction-engines, each weighing 10 tons or 3,300 lbs. per foot width of roller-wheels; two 18-HP. traction-engines of 8 tons each; and one 10-ton traction-roller. All the rollers were provided with grooved front wheels and cleated rear wheels. Each division of the reservoir was lined on the floor and slope with 18 inches of clay puddle, on which was placed a lining of Portland-cement concrete 6 inches thick (Figs. 37, p. 164). On the concrete lining over the whole floor, and extending up the slopes to a point 10 feet vertically below the water-line, was placed a 3-inch mixture of asphalt mastic and grit. In order to prevent slipping of the asphalt mixture on the slopes, the concrete was indented with grooves inch wide and deep, and 4 inches apart. At the end of the dividing embankment was a valve-house, in which were placed all the valves for controlling the water to and from the two divisions, which were provided with separate inletand outlet-pipes, and screen-chambers. As the reservoirs were designed as settling-basins and not as storage-basins, the water was pumped through a 48-inch cast-iron main, laid on the floors and extending diagonally across each division of the reservoir, and was discharged through a series of 48-inch spigot-and-faucet tees, set at alternate angles of 45 degrees from the vertical. The ends of the inflow-pipes were provided with 48-inch upturned elbows. The water passed upwards from the tees and elbows diagonally across the basin to a floating discharge-pipe, consisting of a 48-inch riveted steel pipe inch thick, provided