2 74 



SCIENCE. 



[Vol. XIII. No. 323 



000,000 as against 162,000,000 in 1877. These 311,000,000 equal 

 23.7 per cent of the population of the civilized world. 



Besides these states which tend to the French monetary system, 

 and to an international circulation, there are certain notable excep- 

 tions; as, for example, England, Canada, Germany, the Nether- 

 lands, Scandinavian Union, Turkey, Morocco, Portugal, China, 

 Siam, Japan, the United States, and Brazil. 



EXCAVATIONS FACILITATED BY FREEZING. 



About seven years ago Mr. Herman Postsch of Aschersleben, 

 Germany, conceived the idea that excavations through difficult 

 ground could be facilitated by freezing it by means of cold brine 

 circulated through pipes inserted down to rock or impervious 



.-a I £#- - 



material ; these ground-pipes being perfectly closed at the lower 

 end, and containing a smaller pipe open at the lower end, down 

 which the brine is pumped, rising in the outer pipe, and returning 

 to an ice-machine to be cooled again. 



After some experiments made with a small apparatus, which 

 were so far satisfactory as to make it evident that the process was 

 a success, he undertook the completion of a shaft partially sunk at 

 the Archibald Mine, near Schweidlengen, Germany, which result- 

 ing successfully has induced its application in many coal-fields 



throughout Germany, France, and the Netherlands. There was 

 much need, in Germany especially, of some way of getting to the 

 beds of lignite and coal, of which there are many covered with 

 beds of quicksand that are almost impassable. This process has 

 added materially to the area of available coal-fields. The greatest 

 depth yet reached in this way through water-bearing strata is 250 

 feet, although there is no limit to the depth capable of being 

 reached ; and there has been no failure to accomplish the work 

 undertaken. 



Fig. I shows a shaft being dug and partially timbered up. In 

 practice it is usual to place pipes about 8 inches in diameter, and 

 about 3?, feet apart, in a circle around the space to be excavated. 

 It is of great importance that the pipes be perfectly closed, and 



that they extend not only to the rock, but far enough into it to 

 allow any surface fissures to be frozen, thus preventing as far as 

 possible percolation through the ledge. 



Fig. 2 shows the process applied to an excavation for a bridge- 

 pier, the frozen wall surrounding the excavated space being in ef- 

 fect a coffer-dam. By its application in this way, the last difficulty 

 is removed in the way of bridging the great rivers having deep 

 alluvial beds, where the depth to rock is so great as to preclude 

 pneumatic foundations ; i.e., greater than one hundred feet below 

 the water surface. 



It has been applied once to tunnelling. In digging under a hill 

 occupied by residences in Stockholm, it was feared that the move- 

 ments of the ground would cause the buildings to settle and crack. 

 The inner end of the tunnel was formed into a freezing-chamber, 

 and cold air at a temperature of —67° F. was circulated through it, 

 which effectually hardened the sand to a depth of five feet from the 

 surface, making a material resembling sandstone rock. The freez- 

 ing was continued ten or twelve hours, and then excavation and 

 walling-up proceeded with for the same length of time. About one 

 foot per day was made in this manner. It is often desired to make 

 excavations in this way adjacent to or under buildings where there 

 is danger of undermining the foundations. 



The owners of the American patents, The Poetsch-Sooysmith 

 Freezing Company of New York, have made several improvements 

 in its application to tunnels especially. The first application of the 

 freezing process in this country was in digging a shaft for the 

 Chapin Mining Company at Iron Mountain, Michigan, where a 

 rectangular shaft 15I feet by i6i feet in the clear, and 95 feet deep 

 to the ledge, was sunk through quicksand and bowlders. Twenty- 

 six 8-inch pipes closed at the lower end were sunk to the ledge in 

 a circle 29 feet in diameter ; and a Linde machine, having a re- 

 frigerating capacity of fifty tons of ice per day, cooled the brine. 

 This work was very successful, the ledge being reached in seventy 

 days after the ice-machine was started. A shaft at Wyoming, 

 Penn., is now being constructed in the same way. 



THE LIGNITE INDUSTRY IN GERMANY. 



Among the number of new industries which are making their 

 way in the world, the manufacture of briquettes from the brown 

 coal or lignite deposits in Germany is one which has of late made 

 considerable strides. This process is well described in Engitieer- 

 ing of March 22. Up to within the last ten or fifteen years, these 

 tertiary deposits of lignite, or half-formed coal, were not utilized in 

 commerce, and were only worked in a small way by the local peas- 

 ants for consumption in their cottages. Even this small trade 

 almost died out with the introduction of cheap coal, due to the 

 extension of the railway system, as, owing to the fifty per cent of 

 moisture which the lignite contained, it was impossible for it to 

 stand transport or to compete with coal. 



The beds of lignite in Saxony,vand on both banks of the Rhine 

 near Cologne, are from ten to twenty yards thick ; and, as they 

 are only covered by from five to ten yards of gravel, they are easily 

 worked in the open as quarries, the gravel being removed and 

 used for filling up as the working of the lignite advances. The 

 lignite is of a dark-chocolate color, and, as its consistency is about 

 that of cheese, it can be easily and cheaply worked by means of the 

 pick and shovel. 



Near the surface it contains slightly more moisture ; but, taking 

 an average of the whole thickness, it amounts to about fifty per 

 cent. The decomposition of the wood is not in all places perfect ; 

 and stumps, roots, branches, and trunks of trees are sometimes 

 met with. When these occur too frequently, the lignite is not so 

 well adapted for making briquettes, as, owing to the wood being 

 of a still fibrous nature, it cannot be so readily reduced to powder, 

 which is absolutely necessary for its manufacture into fuel, though 

 of course these remains of trees can be burnt as ordinary wood, 

 and are indeed so utilized. As a rule, however, the mass of the 

 bed is friable, and can easily be crushed in the hand. 



With regard to the formation of these deposits, there are in 

 Germany two theories. The one is that these masses of lignite 

 were formed in precisely the same manner as the coal-seams, but 



