In the accompanying illustration, we present to our readers a mammoth excavator, built by the Osgood Dredge Company of Albany, N.Y., for the Pacific Guano Company of California, for uncovering their phosphate deposits on Chisholm Island, South Colombia.



In order to bring out more clearly the principal problem involved in the construction of this machine, we shall state first the proposed method of its operation. This is as follows, viz.: The excavator is to dig a trench thirty feet wide, down to the phosphate rock, and the entire length of the bed - about one quarter of a mile - dumping the earth of the first cut to one side. The phosphate is taken out behind the excavator. On reaching the end of the bed, the excavator is reversed and starts back, making a second cut thirty feet wide, and dumping now into the cut from which the phosphate has just been removed. In this way the entire bed is traversed, the excavator turning over the earth in great furrows thirty feet wide, and giving an opportunity to simultaneously get out all the phosphate.

As will be seen, the main problem presented was to turn the car around at each end of the cut in a very limited space. To accomplish this, the car is mounted on a fixed axle at each end and on a truck under its center of gravity; this is somewhat forward of the geometrical center of the car. The frame of the truck is circular, thirteen feet in diameter, made of I beams curved to shape. The circle carries a track, on which a ring of coned rollers revolves, which in turn supports the car. By pulling out the track from under both ends of the car, the whole weight is balanced on this central turntable truck, thus admitting of the car being turned, end for end, within its own length. This method of turning the car, and the size of the machine, are the principal features.

The car is 40' × 13', with arched truss sides. The track is seven feet gauge, the spread between tracks 20 feet, the height of the A frame 38 feet, length of boom 40 feet, swinging in a circle of 30 feet radius, and through two-thirds of the entire circle. It has a steel dipper of 46 cubic feet capacity, 1 inch steel chains, 10" × 12" double cylinder hoisting engine, and 6¼" × 8" double cylinder reversible crowding engine. The drums are fitted with friction clutches. Owing to the great distance at which the dipper is handled, its size is reduced, and because it swings on the arc of so large a circle the capacity of this machine is only one-half of that of the No. 1 excavator built by the Osgood Dredge Company. Nevertheless it will do the work of from 75 to 100 men, since its capacity is from 800 to 1,000 cubic yards per day, the amount of rock uncovered depending, of course, upon the depth of earth overlying it. The excavator will dump 30 feet from the center line of the car, and 26 feet above the track, which is laid on the rock. Total weight about fifty tons.

The crew required for its operation consists of 1 engineer, 1 fireman, 1 craneman, and 4 to 5 pit men to tend jacks, move track, etc.

In the illustration the boiler connections are omitted, also the housing for the protection of the crew. The design is characterized by the evident care which has been bestowed upon securing simplicity and durability. - American Engineer.