150 A TREATISE ON DREDGES AND DREDGING 



cylinders and was driven directly by two compound steam cylinders 

 with variable expansion, with condenser. The advantage of this 

 arrangement was that, since the expansion was effected success- 

 ively in the two steam cylinders, the stress upon the piston varied 

 within quite narrow limits. This suited the conditions of the work 

 of compression, as the maximum stress was produced in the com- 

 pressing cylinders during the period of forcing the excavated material. 



The carrier or conveyor consisted of two iron plate pipes with 

 Jandin's joints of steel rings and rubber washers, secured with 

 conical pins. Here and there were arranged flexible joints, which 

 were likewise employed for the jointing of the dredge pipe and the 

 connecting of the floating conveyor with the forcing apparatus 

 carried by the boat. 



The dredge was self propelling. The boat was maneuvered by 

 means of mooring chains anchored at a great distance and payed 

 in and out by four steam winches located one at each corner of the 

 deck of the pontoon upon which were mounted all the machinery. 



Pneumatic dredging is specially adapted to the forcing of the 

 dredged material to a great distance, or to elevating it upon the 

 bank to considerable heights, for the pressure at the beginning of 

 the conduit may easily reach three atmospheres, which would 

 effect an elevation to 95 ft. a height that exceeds the ordinary 

 conditions. When the material is to be forced but a short 

 distance, as emptying it behind a jetty, the system may be so arranged 

 that the dredging and forcing may be effected continuously and 

 simultaneously. The dredging pipe is then prolonged directly to 

 the floating conveyor, to which it is attached by a flexible metallic 

 elbow. 



In hydraulic mining a hydraulic elevator is sometimes used 

 to raise the sluiced material from the bottom of pits and river 

 bottoms. The sluiced material entering the pipe is met by a jet 

 of water under pressure which forces the material to the desired 

 height. The efficiency of the elevator is increased by an auxiliary 

 opening admitting the proper proportion of air. Material is raised 

 in this manner 100 ft. or more. This might be termed a form of 

 dredging. 



