Excerpt from Recent Progress in the Thawing of Frozen Gravel in Placer Mining Dredging methods for gold placers and the construction and opera tion of gold dredges were described in Bulletins 121 1 and 127 2 of the Bureau of Mines. The working of frozen gravels, a special problem in placer mining, has received much attention in Alaska and the Yukon Territory, and the methods evolved there are described in this paper. In placer mining in the far North one of the greatest difficulties encountered is the permanently frozen condition of the ground. In the early days of mining the ground was thawed by the primitive method of building wood fires on the surface, at the bottom of a shaft, or at the face of a drift. Although this method was slow and costly, a more effective one was not discovered until about 1898, when Mr. C. J. Berry3 noticed that the steam escaping from the exhaust of a hoisting engine had thawed a hole in the solid muck. Mr. Berry picked up the exhaust pipe (a rubber hose), applied it elsewhere, and found the steam thawed the ice and moss so rapidly as to permit the full length of the hose to penetrate the ground Within a few minutes. Further experiments followed. At first a rifle barrel and then a short piece of iron pipe, pointed at one end, was used for penetrating the ground, rubber hose being attached to convey the steam. The direct application of steam through points proved so effective that it became the chief method adopted in thawing many millions of cubic yards of gravel for drift, surface mining, and dredging operations. As a result of experiments, changes were made in the shape of the steam point, better methods of application were devised, and the best number of points to be used in a unit and the distances at which points should be spaced to get the maximum benefit were determined. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.