Frost as a Servant.
Cold as well as heat may be employed in a novel manner. The flesh of birds, beasts, and insects is now frozen hard, so as to be sliced into extremely thin sections clearly showing the details of structure. How a freezing process may aid the miner was shown first in Germany in 1880, when Hermann Poetsch, a mining engineer, had to sink a shaft near Aschersleben, to a vein of coal, where, after excavating 100 feet, a stratum of sand eighteen feet thick, overlying the coal, was encountered. It occurred to Poetsch that the great difficulty occasioned by the influx of water through the sand could be overcome by solidifying the entire mass by freezing. To do this, he penetrated the sand to be excavated with large pipes eight inches in diameter, sunk entirely through it and a foot or two into the underlying coal. These were placed in a circle at intervals of a metre, and close to the periphery of the shaft. They were closed at the lower end. Inside each of these and open at its lower end was a pipe an inch in diameter. This system of pipes was so connected that a closed circulation could be produced down through the small pipes and up through the large ones. An ice-machine, such as brewers use, was set up near by and kept at a temperature below zero Fahrenheit. A tank filled with a solution of chloride of magnesium, which freezes at -40° Fahr., had its contents circulated through the ground pipes described. Thermometers placed in pipes sunk in the mass of sand showed 51.8° Fahr. at the beginning of the process. The circulation was kept up and on the third day the whole mass was frozen. Within the continuous frozen wall the material was excavated without damage from caving in or inflow of water. The freezing entered the coal three feet, and to a distance six feet outside the pipes. The circulation was kept up until the excavation and walling were complete. On a somewhat similar plan tunnels have been bored through difficult ground. Of late years at Detroit, and elsewhere, serious breaks in water-mains have been repaired after a freezing process has solidified the stream.