Frozen Coal Shafts.

Kaipara and Waitemata Echo, 10 July 1914, Page 2

Frozen Coal Shafts.

It was not until 1883,' when P-ootsch invented the " freezing method," that Holland's coal fields became of any practical value. The coal is found in the province of Limburg, and, what is more, the two mines near Kerkrade in that province Were the very first coal mines operated in continental Europe in mediaeval times. When, after iB6O, the mining undustry came to be more seriously considered, and several concessions -had been given out by the Dutch Government, it was found that the coal layers could not properly be reached, for in every place except in the two mediaeval mines near Kerkrade, where coal is encountered immediately under the solid rock, there is a stratum of drift sand that contains great quantities of water. This condition of things made it practio: ly impossible to build the shafts, whi'.-h had to be of considerable depth, for the coal layers are encountered at a depth of from 300 to 1000 feet. The freezing method, however, has successfully solved the problem, and Holland now has a flourishing mining inclus-

try. On the spot where the shaft is to be dug, frdm 25 to 30 borings are made down through the drift sand to the solid rock in a circle five feet larger in diameter than the projected shaft. Pipes are then sunk into these boreholes, and through these is circulated, by powerful freezing machines, a chemical solution cooled down to minus 20 deg. Cnt. In this way the drift sand containing the water is frozen as hard as a rock after the freezing machines have been working day and night for two months. In this frozen cylinder of sand a "shaft is then dug and lined from bottom to top with strong segments of cast iron securely soldered together with lead. ■ ' m