872 Transactions op the American Instittjte. 



has become nearly the universal method, where the currents are 

 rapid and river beds treacherous. 



Among the eminent engineers who have used this plan, may be 

 mentioned Cubitt, Hawkshaw and Simpson, past-presidents of the 

 Institution of Civil Engineers of London, and Brunei, Hemans, 

 Brunlees, Page and Fox, Rawlinson, Brereton, Fitzgibbon, Brassy 

 and many more of the prominent engineers of England, besides a 

 great many of the continental engineers. 



The common method of using the pneumatic process is as fol- 

 lows: The pile consists of a number of hollow cast-iron cylinders,* 

 A A, about nine feet in length, provided with flanges on the inside, 

 by which they are bolted together, one on the top of the other, 

 until the desired length is obtained. From a platform on tempo- 

 rary wooden piles, or large scow boats, a derrick is placed which 

 .vsusiiends the column and lands it, with the end on the bottom of 

 ^he river in the place where it is to be driven. Another cylinder, 

 iS, called the air-lock, is placed on top of the column, usually made 

 of boiler iron, with a top and bottom plate of cast-iron, in which 

 =are man-holes, C (7, that can be closed at pleasure by plates, D D, 

 with Jiinges opening on the lower sides and lined with rubber at 

 the joints. In the top and in the diaphragm or lower plate are air- 

 cocks, E E. Leading from the outside of the air-lock, near the 

 bottom, .are two curved tubes, F, which also pass through the dia- 

 phragm :£Qid are closed by cocks. The air-lock is bolted to the top 

 of the column. Small air-pumps usually worked by a small steam 

 engine are connected with one of the curved pipes in the air-lock 

 by means -of a flexible tube. The lower man-hole plate is then 

 closed, and .air is forced into the column. 



With the first stroke of the pumps, the operation of compressing 

 the air commences, and as this pressure increases it forces the 

 water out through the open bottom. This continues until the 

 pressure of air equals that due to the head of water outside the 

 column, and the water has all been forced outside. The workmen 

 then enter the air-lock, and closing the upper man-hole a cock is 

 opened in the lower diaphragm, and the compressed air from below 

 is admitted. When the pressure has become equalized the loAver 

 man-hole plate falls open and the workmen can pass down on 

 ladders to the bed of the river to excavate the material in the 

 column. This is raised in canvas bags to the air-lock by means 

 of a drum, the shaft of which passes through stufl5ng-boxes to the 



• See Diagram. 



