320 



ENGINEERING. 



front of it. In very loose ground jets of water 

 under high pressure can be thrown out to loosen 

 the ground in front of the caisson. The direc- 

 tion in which the caisson is moved is under 

 perfect control, and all the parts are loaded so 

 as to overcome the buoyancy. The work may 

 be prosecuted without reference to the weath- 

 er as soon as deep water is reached. If the 

 tunnel is intended for a water-supply, the cais- 

 son may be fitted with interior filters and gates, 

 and left in position to serve as a permanent head- 

 works for the tunnel. 



The Poetsch Method of Mining. An ingenious 

 method of overcoming the difficulties incident 

 to sinking shafts or driving galleries through 

 excessively watery soils has been invented by 

 Mr. Poetsch, a German engineer, and has been 

 successfully used in several instances, notably 

 in the Stockholm tunnel, mentioned elsewhere, 

 and in the Konigs Wusterhausen mine, near 

 Berlin. The method consists in freezing the 

 semi-liquid earth so that it can be excavated 

 by ordinary methods, and without the need 

 of pumping. The congelation is effected by 

 sinking a number of sheet - iron pipes eight 

 and a half inches in diameter, so that they 

 surround the intended shaft at intervals of 

 about five feet. The holes for these pipes are 

 bored or digged, according to circumstances. 

 When in position the lower end of the pipe 

 is hermetically sealed by lowering leaden 

 plugs and pouring cement on top of them. 

 This done, small central tubes are introduced, 

 having openings near the lower end. Into the 

 upper ends of these interior tubes the freezing 

 mixture is poured. It finds its way out through 

 the openings referred to, and ascends through 

 the annular space between the tube and pipe. 

 The liquid becomes heated in its passage at the 

 expense of the surrounding earth, and, after a 

 time, provided the difference of temperatures 

 be sufficient, the pipe becomes incased with 

 a cylinder solidly frozen earth, which gradu- 

 ally increases in diameter until it unites with 

 the frozen cylinder of the next pipe. Thus is 

 formed a frozen wall surrounding the space 

 to be excavated. By waiting long enough, this 

 space may be wholly solidified, but it is more 

 economical to begin work as soon as the sepa- 

 rate columns of frozen earth are solidly united. 

 This union occurs first at the lower ends of 

 the pipes, and ascends with greater or less 

 rapidity till it approaches the surface of the 

 ground. Mr. Poetsch used the chlorides of 

 magnesium and of calcium, which latter is 

 cheaper. The solution contains 19 per cent, 

 of the salt, and has a density of I'lV, with a 

 specific heat of 0*9. Under these circum- 

 stances it solidifies at about 40. After 

 passing through the tubes the fluid is con- 

 ducted to a refrigerating-machine, where it 

 is relieved of the heat absorbed in passing 

 through the earth, and is again ready to repeat 

 the freezing process (see ICE, ARTIFICIAL). Mr. 

 Poetsch has used the Carre machine, which 

 utilizes the affinity of water for ammonia, and 



induces a temperature of 25 to 30. A 

 circulating pump is necessary, with a forcing 

 arrangement, to keep the fluid in circulation, 

 through a system of pipes. The shaft is lined 

 with well-seasoned timber as fast as the work 

 proceeds, so as to relieve the ice-wall from all 

 avoidable strain. 



Draining the Pinsk Marshes* About midway be- 

 tween the Baltic Sea and the Black Sea the 

 best maps show a tract of uninhabitable 

 marsh-land, lying on both sides of the Pripet 

 river, a branch of the Dnieper, and crossed 

 by other smaller streams. The area of this 

 marsh is about equal to that of the State of 

 Pennsylvania, and until recently it has been a 

 safe harbor of refuge for many an outlaw. In 

 1870 the Government, after careful surveys, 

 began the work of reclamation. A large force 

 of engineers and a detail of several thousand 

 troops were sent to the borders of the swamp, 

 and have been at work ever since sinking wells, 

 building bridges, constructing dikes, and reduc- 

 ing the forest-jungle so that hereafter it can be 

 regularly cut over as are all the preserved forests 

 of Europe. About 4,500,000 acres had been 

 reclaimed at the end of 1886. Of this 240,000 

 acres are excellent meadow-land, 901,966 acres 

 are semi-arable woodland, 499,179 acres of wild 

 forest are accessible through navigable canals, 

 and 2,009,036 acres are good arable land, of 

 which, however, only a small proportion (123,- 

 577 acres) are as yet under cultivation. In 

 addition to a large number of canals, drains, 

 and embankments, 179 bridges were built, 572 

 wells were sunk, varying in depth from 20 feet 

 to 100 feet. This is one of the most praise- 

 worthy feats of engineering ever undertaken 

 by the Russian or any other Government, and 

 is a peaceful victory for which even nihilism 

 should give credit. After the work is finished 

 it should take but a few years to convert the 

 whole region into a prosperous farming dis- 

 trict, not to be distinguished from other com- 

 munes bordering the sources of the Dnieper. 



Lartigne's Single Railway. The general plan of 

 this very simple and economical railway is in- 

 dicated in the illustration. The unit of con- 

 struction is an A-shaped frame of angle-iron. 

 A series of these is set up with the legs bolted 

 to sleepers and connected with each other by 

 side-rails and a top-rail, which latter sustains 

 the principal wear and tear of service. The 

 rolling-stock is made to ride upon this struct- 

 ure like a saddle, the main wheels resting upon 

 the top-rail, while side-wheels bearing upon 

 the connecting side-rails prevent undue oscil- 

 lation or tilting. Single railways are no new 

 thing. Other systems have preceded Lar- 

 tigue's, notably M. Haddon's ; but Lartigue's 

 combines many practical improvements in de- 

 tails, and seems to have reached a limit of 

 economy, and, as it has certainly demonstrated, 

 a high efficiency. In September, 1886, an ex- 

 perimental line was erected in London. In 

 this country none is as yet in operation. Be- 

 fore describing the appliances more in detail, 



