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wards it was applied in America in sinking a shaft at the Chapin Mine, Michigan. The Engineering News describes the system adopted at that mine : — " The owners of the American patents, the Pcetsch-Sooysmith Freezing Company, contracted to freeze, excavate, and curb up a rectangular shaft 15} ft. x 16} ft., and about 100 ft. deep to the ledge. The mining company put the freezing-pipes into the ground 3ft. apart, in a circle 29ft. in diameter, and, with the exception of two of the pipes, to the ledge. This proved to be a difficult task on account of the many boulders encountered. A lOin. casing-pipe with flush joints was first drilled down by various means, a drill being worked within the pipe when necessary, and the material removed by jetting or by a sand-pump. The casing-pipe being once down to the ledge, a freezing-pipe was placed inside, and the outer casing-pipe drawn up and used for the next pipe. The freezing-pipes left in the ground were Bin. in diameter, the lower ends being closed. "Inside of these Bin. pipes were placed pipes l}in. in diameter, Open at the bottom. These inner pipes, as well as the outer pipes, were connected together at the top of the ground, forming a complete circuit, through which a cold brine was circulated. " The brine used was a solution containing about 25 per cent, of calcium chloride, which has a very low freezing point. The brine was coo ed with a Linde ice-machine, made by F. W. Wolf, of Chicago, having a refrigerating capacity of 50 tons of ice per day. The ammonia was compressed to about 1351b. per square inch, and cooled by passing through coils immersed in water kept cold by pumping from a brook. Then the ammonia was allowed to expand through coils immersed in brine, and finally returned to the compressor. " The temperature of the expanded ammonia was such as to cool the brine to a few degrees below zero Fahr. This brine being circulated through the ground-pipes, was raised in temperature about 2° Fahr. After forty days' freezing an ice-wall 10ft. thick was formed around the shaft. The excavation—commenced soon after starting the ice-machine —had in the meantime reached a depth of 40ft. Thirty days more sufficed to reach the ledge. " The shaft was, for convenience, curved as the excavation proceeded. This was, however, not necessary, as the walls would have stood vertically throughout the whole depth very well. The temperature of the air within the shaft was generally below the freezing-point, and there was no indication of the exposed material thawing. The curbing was made of horizontal sets of timber, 16in. square, placed 2ft. apart, with 4in. vertical plank behind the timbers. The cross walls were placed in afterwards. " The timbering was supported from one set to another by bolts placed near the corners of the shaft, the whole system being suspended from cross timbers at the surface of the ground. The unfrozen area within the shaft grew less as the actual running time of the freezing-machine increased. When a stratum of boulders was encountered, the frozen area reached nearly across the shaft ; but when quicksand containing a large percentage of water was passed through, the unfrozen area was greater. The reason of this is readily understood when it is remembered that the specific heat of water is about five times as great as that of any of the other materials, and therefore the strata containing most water would require more cold, and would be longer in freezing. " The frozen quicksand resembles sandstone. The corners of broken pieces were hard and sharp. Granite boulders embedded in it showed a decided tendency to fracture across rather than break loose. The tensile strength of the frozen ground, as determined by a cement-testing machine, was equal to that of the best neat Portland cement, and varied from 3501b. to 4501b. per square inch ; and its strength against crushing, as determined from inch square cubes, was 8501b. per square inch. " This furnishes data from which the strength of the surrounding frozen wall may be computed as an arch. An ice wall 10ft. thick will be found sufficiently strong for any case likely to occur. Near the bottom the freezing extended within the circle solidly to the centre. It is not known how far it extended outside, as no borings could be made through it. A test-pit was sunk outside the shaft as far as the water could permit (some 22ft.), and from this it appeared that the freezing extended outwardly from the pipes at that point about 13ft. " The material was mostly loosened by picks and chisel bars. Black powder was used for blasting for a considerable time, but this was discontinued for fear the concussion might injure the pipes or fracture the wall. The material was hoisted out by an iron bucket, which also took out the water which stood in the unfrozen centre. There was no appreciable inflow of water until the excavation had reached nearly to the ledge. " On reaching the ledge it was discovered that it was so fissured and disintegrated as to allow water to come in under the frozen wall, at a corner in the vicinity of one of the pipes that did not extend to the ledge. On 20th February, the incoming stream had so worn a channel as to permit a jet of sand and water Sin. in diameter to enter. "The shaft was allowed to flood, water being pumped into it at the same time, to prevent as much as possible the flow of water through the opening. " An Bin. freezing-pipe was put in place in the shaft, the foot being directly at the opening, the purpose being to freeze the leak off. " Cold brine was circulated through the whole system of freezing-pipes for ten days uninterruptedly, when the water was pumped out, and the seam was found to be quite closed; but there was still a small amount of percolation through the ledge, requiring occasional pumping to clear the shaft; ice had collected several inches thick on the side of the shaft and several feet in the corner, where the extra freezing-pipe was placed. " The work of removing the sand which had come in with the water and the clearing up of the bottom continued for two weeks, when the water from the ledge increased at such a rate that it was decided to lay short auxiliary freezing-pipes against the leaks and freeze the ledge itself. This was done, the shaft was flooded again, and the brine was circulated thirty days. When the water was pumped out, the leakage was found to be small and the excavation was proceeded with. The soft,