Wooden handles are fastened to the sides which enable the operator to guide and to trip the scoop. This type of scraper is not economical to use on hauls of over 150 ft. They are, however, a good means of excavating in places where wagons could not be readily handled.

Wheeled Scrapers.-A wheeled scraper (Fig. 6) consists of a steel box with one open side suspended from an axle which is supported by wide tread wheels of about 40 in. diameter. Attached to the box are levers which enable the operator to raise, lower, or dump the scrapers as desired without stopping the team. The box is of the form of a rectangle, square on the bottom and having a height of about its depth. Its chief usefulness commences about where that of the drag scraper ceases and is an excellent method of moving earth or hauls up to about 1000 ft.

1d. Buckets. Many types of buckets are used in excavation. The clam shell and the orange peel are employed as diggers. Handling buckets are loaded by hand or from hoppers.

FIG. 7.-Owen clam-shell bucket in operation,
Owen Bucket Co., Cleveland, Ohio.

Clam Shell Bucket.-The clam shell bucket (Fig. 7) consists of two curved jaws which, when closed, form half of a short cylinder. Two sets of steel arms connect these jaws to the head casting. The lower end of each set is connected to the outer edge of the jaws, and the upper ends are hinged to the head casting. The inner edges of the jaws are connected together and hinged to a counterweight. The counterweight is connected to the head frame through sheaves and the closing line to the head casting.

Two lines are necessary for operation, a closing line and a holding line, each acting as its name implies. By means of the counterweight, the bucket will open when the closing line is released, causing the jaws to separate. On engaging the closing line, the jaws will tend to close, causing the bucket to bite into and fill with earth.

Clam-shell buckets may be supplied with teeth to aid in digging in hard ground. The arrangement of sheaves and hoisting line plays an important part in the digging ability of a shovel. The Lakewood Engineering Co. makes a bucket which has a sheave mounted on each jaw arm, thus giving better digging ability through combination of leverages. Boulders may be handled by clam shells which are too big to fit in the bucket, as the grip of the jaws is sufficient to hold them.

Orange Peel Bucket.-The orange peel bucket (Fig. 8) consists of three or more curved triangular steel blades which when closed, form a half sphere. The points of the blades are

reinforced, as teeth are not used with this type of bucket. From each blade, one arm extends to the head casting and another to the counterweight. Two lines are used to control the operation, one known as the closing line, which closes the bucket, and the other the holding line. The holding line takes the dead weight of the bucket, when the closing line is released, to allow the bucket to open.

The orange peel bucket will dig in more resistant material than will the clam shell. Small or dwarf orange peel buckets are used in sinking sectional piling in cramped quarters, as in underpinning buildings.

Handling Bucket.-Steel buckets used for handling material are of many different sizes and shapes. They are classified according to the manner in which they discharge-i.e., tilting or bottom dump buckets.

The tilting bucket is hung by a heavy bail hinged to the sides of the bucket which is held in the upright position by a catch. This bail is fastened a little above the center of gravity of the empty bucket so that little effort is required to dump the bucket and it automatically returns to its upright, locked position. ROUND BUCKETS, HEAVIER BOTTOM THAN SIDES

The bottom dump bucket discharges through doors in the bottom. The sizes of these buckets and the method of opening the bottom vary with different manufacturers. In general, the bottom dump is square, the doors being opened through a leverage system actuated by a man stationed at the point of unloading. Some buckets are e quipped for a double line enabling the hoist and discharge to be controlled by one operator.

1e. Picks, Shovels.-Where the amount of excavation is small and power operated tools cannot be advantageously employed, hand methods must be used. With these, the ground is first broken up or loosened and then loaded into barrows and wagons for removing. Three tools are used for thus loosening ground-the pick, mattock, and plow.

The pick consists of an iron arc, one end of which is pointed, the other slightly flattened, attached at the center to a wooden handle.

The mattock is similar to the pick but has a broad flat edge at one end. This tool is used in very loose soil or for trimming or leveling.

The plow as drawn by one, two, or four horses will be found to be an excellent means of loosening soil. The size of plow and number of horses required will depend on the nature of the ground. In ordinary loam a team should loosen from 40 to 50 yd. per hr., which is 10 to 12 times the amount a man with a pick can do in the same time. Shovels should be selected as to their wearing ability and the nature of their intended use. A shovel may be regarded as a cutting and conveying tool with the steel part supplying the cutting edge; and with the handle, the means of conveying. The shape of the cutting edge will therefore depend on the material to be handled; and the length of handle will depend on the distance the material is to be moved, and the working space. A shovel holding a load of 21 lb. is considered to be the most efficient as regards size. A round pointed shovel would be used for digging in hard ground; whereas, a square pointed one is suited for loose materials, such as sand, or for handmixing concrete.

2. Rock Excavating Equipment.-When rock in any quantity is encountered in excavating, some means must be employed to break this up into sizes which can be handled and removed. Two general means for this purpose are at hand-explosives or plug-and-feather. In crowded quarters, where injury to other buildings by the jar or by pieces of flying rock is liable to occur, the use of explosives is limited. However, this means has been employed even under the above circumstances and may have to be resorted to where the rock encountered is hard and not easily split, either by hand or machine, to a size which may be handled by the mechanical means available.

In all cases where an explosive is used, great care must be exercised; and in most localities certain rules are in force as to its storage, handling, etc. Usually a licensed powder man is required for this work.

2a. Explosives.-Explosives are divided into two classes dependent upon the force exerted-i.e., black powders, which are weakest, and dynamite and granulated nitroglycerin powders, which are the strongest. Both require the utmost care in handling and storage.

An explosion results from chemical action between the components of the explosive, freeing a relatively large volume of gas at high temperature with greater or less rapidity. The force exerted by this gas is equal in all directions at the instant of explosion. "Tamping" and the shape of the hole will therefore affect the result of the explosion. In every case the explosive should fill the hole leaving no air cushions. Tamping, therefore, becomes of particular importance with the weaker explosives. Further, all holes before charging should be cleaned out and water removed. If seepage occurs so that it is not possible to keep the hole dry, a waterproofed wrapper about the charge must be used, else the desired explosion may not occur and removing an unexploded charge is dangerous.

Black Powder.-Black powder is a slow burning powder. It consists of 65 to 75% potassium nitrate, 15 to 20% charcoal, and 10 to 15% sulphur. This powder is obtained in kegs weighing 25 lb. or more; and is poured through a funnel or tube to prevent any of the powder sticking to the sides of the holes. In cases where the powder cannot be poured, it is made up in a paper cartridge and lightly shoved in with a stick. Such a container may be readily made by wrapping brown paper on a mandrel slightly smaller than the hole. If necessary, the container may be dipped in hot paraffin and made waterproof.

Black powder may be fired by a battery, or by a fuse which is a core of gunpowder, surrounded by tape. One end of the fuse is inserted in the powder before tamping. As the rate of burning of the fuse is known, enough should be used to enable the operator to reach a place of safety. An "electric squib" resembles a fuse but has a paper cap instead of a copper one. In either, a spark ignites the powder.