Powder is graded according to the size of the grains, smaller grains giving quicker burning powder than large grains. A good powder is dark gray or slate color, and should leave no dust. When burned on a sheet of white paper, it should leave no residue.

Dynamite and Nitroglycerin.-Nitroglycerin is the basis of the more powerful explosives. It is extremely sensitive both to heat and shock and for this reason is not used full strength. Dynamite is any absorbent material saturated, or partly saturated, with nitroglycerin. It is known as "active" or "inactive" according to the nature of the absorbent material, commonly called "dope." Porous earth and wood pulp are known as "inactive dope" as they do not take part in the explosion but act as a means of supplying the nitroglycerin. Gunpowder is known as "active dope" as it takes part in the explosion.

Dynamite is rated on its percent by weight of nitroglycerin when absorbed by "inactive dope," i.e., a 40% dynamite would contain 40% by weight nitroglycerin but has an explosive strength equal to that of 40% "inactive dope" dynamite.

Dynamite is commonly packed in paper cartridges from 6 to 16 in. long and % to 2 in. in diameter, the most common size being 11⁄2 × 8 in., weighing about 1⁄2 lb., and is shipped in boxes of 25 to 50 lb.

A strength of 40% is most commonly employed and a number of brands of various composition are on the market. Three brands of different strength will serve to illustrate these:

So many

Dynamite, while an effective tool in the hands of one who thoroughly understands it, is dangerous. factors enter into its behavior and affect it each in a different way, that only experienced men should handle it. Tamping should not be omitted as greater force is secured when the gases are confined. Sand may be poured in first to fill all cracks around the charge, followed by stiff clay rammed in lightly at first and then harder.

In charging, the sticks should not be rammed into the holes and in no case should an iron bar be used. Dynamite requires a shock to detonate it, which is supplied by a copper cap containing fulminate of mercury in which is embedded a platinum wire. This is connected by wire to a blasting machine, which is a means of generating current to heat the platinum wire, thus exploding the fulminate of mercury which, in turn, detonates the dynamite.

Building laws in various states cover the case of "misfire." In New York "tamping" may not be removed from a "misfire" nor can drilling proceed in a hole not completely fired to the end. New holes must be drilled not less than 12 in. from those which have "misfired." The cause of misfire may be traced to a number of things. The principal causes are: defective cap, break or short circuit in the wires, cap too weak, battery overloaded or improperly operated.

26. Rock Drills.-Drilling in rock may be carried on by hand, by churn drills, or by machine drills. Hand drilling, unless the number of feet to be drilled is small or the work carried on away from means of getting steam or air, is not much used in building operation. Machine drills are more largely employed. The smaller types of machine drills are made light enough so as to be readily portable and easily handled by one man; in larger sizes they are mounted on tripods and adjusted to drill horizontally at an angle, or vertically. The smaller drill will generally be found to be handiest except in cases where long holes and hard rock are encountered.

Hand Drilling.-Hand drilling is done by one, two, or three men. Where one man is employed, he both holds the drill and strikes. In soft rock or in constricted quarters, and for

shallow holes, this is generally considered the most economical. The weight of hammer used is 4 to 5 lb. As the hole becomes deeper, a heavier blow is advantageous and two or three men are used, one to hold and turn the drill after each blow and one or two strikers. In such work the hammer weight is about 10 lb. Light blows, delivered in quick succession, are better than heavy blows having long intervals between. For this reason two and sometimes three strikers are employed. Drilling, like every other operation, requires skill and judgment on the part of the strikers to know how to strike the drill in order to cut and keep the bottom of the hole clear so that the drill is operating on solid rock and not on loose fragments..

Water is generally supplied to the drill to keep the powdered rock in suspension, forming a paste which must be removed from time to time. This is done by a "spoon," a long bar with the end flattened and bent slightly at an angle to the bar. Waste attached to a stick will also clean the hole.

Drill steels vary in size for different methods of drilling. A drill of 4 to 8 in. in diameter is most commonly used when one man is employed. The diameter of the cutting edge depends on the size hole required but is generally to 1⁄2 in. larger than the diameter of the rod. Octagonal steel is used for the shank as this offers a better grip than the other shapes. The cutting edge is made slightly curved to insure a starting point and to allow for any tilting during the first few inches. Hand drills, or "jumpers" as they are called, are made in different shapes. The chisel bit is the one most commonly used with hand drilling. Star and rose bits are used when holes are to be drilled in cement or brick work for the placing of expansion bolts, pipes, etc.

Churn Drilling.-Churn drilling consists of lifting a drill rod a foot or more and then allowing it to fall. The drill is generally double bitted; and in the hands of skillful men, this method is good for drilling deep holes. The number of men may vary from one to six, but with the latter number it is best to provide a platform, with three men on the ground and three on the platform. Cross pieces or arms are bolted to the drill for lifting. One is provided for each pair of men. For shallow holes of small diameter a ball is welded to the shank to give additional weight. When this is done the drill is known as a "ball drill."

The bits used are the same as for the "jumper" drill and are generally made of short sections of tool steel welded to each end of an iron bar or pipe. The blow depends on the weight and velocity of fall but care must be used that the weight is not excessive, as there will be a loss of efficiency if too many men are required to handle the drill.

Machine Drills.-Machine operated drills may be divided into two main classes according to whether the drill steel acts as part of the piston or as a separate unit. The former is called a "piston drill," and the latter a "hammer drill."

Piston Drill.-The piston and piston rod in the piston type are made integral. A U bolt chuck is attached to the piston rod, into which the drill steel is clamped. These drills are mounted on tripods and are used where long holes, hard rock, and high air pressures pre oil. In general, tripod drills are used on outside work, as due to their weight and space required to set up, they are not adaptable to cramped quarters.

Rotation is provided by either the up or down stroke. allow the rifle bar to fit into it. latter.

means of a rifle bar, ratchet, and pawls; and may take place on The top of the piston is hollow and rifled on the inside so as to The rifling may be either right or left-hand, but is usually the

Two methods are employed to actuate the piston. Either the piston in its movement covers and uncovers ports, or the movement is controlled by a separate valve or valves. Drills

of the first type are now practically obsolete. The tappet and auxiliary valve drills are perhaps the most common of the second type.

Some manufacturers combine these two. Fig. 12 shows in section the combination as used in the Sullivan "Hyspeed" drills, in which the advantage of each is retained. The main valve is of the spool type composed of three spools of the same diameter, fitted in a straight bore chest and controlled by the air pressure. Below is a small flat shuttle valve actuated by a light rocker, whose ends engage inclined surfaces on the piston. The duty of the tappet valve is to alternately admit and exhaust pressure from each end of the main valve. The rocker is shaped like a gear segment, the projection at the top corresponding to a tooth of a rack. This projection engages with and operates a flat valve of the double "D" type which controls the admission of air to the cylinder.

Either of these valves may be used separately. The Sullivan "Liteweight," section of which is shown in Fig. 13, uses only the spool or air valve. The length of stroke and force of blow can be varied with the piston type of drill from the full force, full stroke, to the light short stroke required at starting.

Piston drills are mounted on tripods for vertical work and on bars or columns for horizontal drilling. Weights are fitted to the legs of the tripod to give additional stability and the columns are held rigidly in place by screw jacks. Mounted on the tripod or columns is a cradle which carries the feed screw and engages tapped lugs of the drill. Slides on the sides of the drill run in grooves of the cradle. The weight of piston drills unmounted, depends on the size of piston and length of stroke.

and be either right or left-hand.

Hammer Drill. Of the two types of machine operated drills, probably the type known as the "hammer drill" is the most commonly used in building construction, and is operated by either steam or air (Fig. 14). While electric and gasoline drills can be obtained, by far the majority of work is done by the air hammer type. This drill is made by a number of manufacturers, the principal difference in design being in the valve control and means of rotating the drill steel.

In general, a drill hammer consists of a casing which contains all the moving parts, having a T-head handle at one end and a "steel holder" at the other. The blow is delivered by a light piston with a short stroke under pressure of 100 to 125 lb. per sq. in. The piston may either strike the end of the steel direct, a collar being welded on an anvil block, or a striking pin may be interposed. One end of the piston is bored out and rifled on the inside to allow the rifle bar to enter. The rifle bar has an enlarged circular head carrying pawls which engage with the ratchet ring, and provides for positive rotation of the piston. The other end of the piston is grooved and fits into corresponding grooves of the chuck rotating the latter and at the same time, the steel. Rotation may be accomplished on either the up or down stroke

In order to have a quick acting piston, the parts are made large and the valve action must be correspondingly rapid. Three types of valves will be taken to show the action. The butterfly valve consists of a simple piece of steel oscillating on a trunion, operated by difference in air pressure on the wings, and therefore requiring but a small As the action is a short lift, friction is amount of power. This steel valve is fitted in the valve chest as shown.

reduced to a minimum and wear on the surfaces is avoided. Its action is positive and, due to its small movement, rapidity is insured.

The tappet and differential spool are two other types of valve used in the hammer type of drill, and have been described under piston drills.

The feed in vertical holes depends on the weight of the machine, but where holes in some other direction are desired, tripods or columns are generally used if the length of hole would tire a man to hold the drill. Small cradles may be obtained in which the hammer drill is clamped. These re light and the drill may be quickly mounted in them when it is desired to use a tripod.

Drill Steel and Bits.-As high grade alloy drill steel requires low heats and great care in forging, a good carbon steel is more often used. Hollow steel bits are more difficult to temper and dress than are solid bits. The nature of the rock and size of hole should

govern the grade of steel chosen. Octagon, hexagon, and round are the shapes commonly used, the first being in special favor as it offers more grip to the chuck and therefore is rotated better. Steel may be obtained in lengths of from 2 to 25 or 30 ft.

Drills may be forged, dressed, and tempered, either by hand or by a special machine. Where the operation is large, machines should be employed as they will give better, faster, and more uniform results. The design of the bit will play an important part in the cutting speed; and here again the size, shape, and temper will depend to a degree on the rock encountered. The bits shown in Fig. 15 are most commonly used in American practice. Bits of several types are shown in Gillett's Handbook of Rock Excavation, together with a description of use, etc.

FIG. 15.-Drill bits, Ingersoll-Rand
Co., N. Y.

MATERIAL TRANSPORTING EQUIPMENT

BY NATHAN C. JOHNSON

3. Wheelbarrows.-Wheelbarrows for construction work are preferably of all steel construction (Fig. 16). The box of such barrows is made in a variety of shapes and sizes to meet different requirements. Where the material to be handled is semi-fluid, barrows having a deep box should be used. The efficient use of wheelbarrows is limited to about 150-ft. runs, and in general, it will be found better to have men to load other than those running the barrows so that the barrow may be in transit a greater portion of time.

4. Wagons. The type of wagon in most general use for building construction purposes is known as the drop bottom. Two other types, though not so extensively used, are the slat bottom and end dump.

Slot bottom wagons require the team to be stopped for unloading and an extra man to help remove the slats. End dump wagons may be of advantage where it is desired to unload into hoppers, or in building embankments, as shoveling is cut to a minimum by backing the wagon to the edge of the embankment and tripping the box latch, so that the contained material flows to place by gravity.

Drop bottom wagons are made in various sizes ranging from 1 to 5-cu. yd. capacity, the size to be used depending on the conditions of haul and the loading arrangements. Wagons of 1 to 21⁄2 cu. yd. are the most common. This wagon is built like a rectangular box with sloping ends and side boards. The bottom of the box consists of two doors opening downward. One side of each door is hinged to the side boards, the other is connected by chains through pulleys to a drum under the driver's seat. On reaching the place of unloading the driver frees a catch which permits the doors to open and releases the load. The doors are brought back to the closed position through a ratcheted lever operated by the driver during the return trip. Except for the time required to load, this type of wagon is continuously in actual transit, as it is not necessary to stop for unloading or for closing the bottom.

Bottom dump wagons are strongly built and should last from 5 to 6 yr. without undue repairs. They are equipped with heavy tires of broad tread which enables them to be used in fairly soft ground. The average speed of horse drawn wagons is about 2 mi. per hr. so that with speed as an item on long hauls, economy may lie in the use of automotive trucks.

5. Auto Trucks.-Automobile trucks, where speed and long hauls are incident to a construction, are found effective and economical. Auto trucks are made in a large number of sizes and types and are rated in ton capacity instead of cubic yards. Their capacities run from 1 to 10 tons, with 1, 3, and 5 tons the most common.

Dumping of auto trucks is accomplished by raising the front part of the body through power means provided for this purpose, the material sliding out through the tail gate. Trucks may be 2 or 4-wheel drive and 2 or 4-wheel steered. Each has its advantages and special uses. Where the roads are soft and muddy, a 4-wheel drive is generally considered better than a two, as a greater number of drivers are brought into play. Two wheel drives are more common at present and give satisfactory service under most conditions.

The use of light weight trucks, many of them fashioned from pleasure car chassis of one make or another with the addition of ready-to-fit bodies and reducing drive parts, is worthy of careful consideration on small operation where the cost and upkeep of larger trucks would not be warranted. These have repeatedly proven themselves economical and useful adjuncts on work of this character.]

PILING AND PILE DRIVING EQUIPMENT

BY NATHAN C. JOHNSON

6. Sheet Piling.-Sheet piling, made either of planks about 2 X 12 in. in size, or of steel shapes, is driven before the excavation is begun and generally to below the grade of the final excavation. Its function is to prevent the leakage of water or of soft materials, such as quick sand, and to withstand the lateral pressure of adjacent ground.

FIG. 17.-Wakefield wood sheet piling.

6a. Wooden Sheet Piling.-When timber is used, the planks are driven close together and, to secure water-tightness, are made double and triple lapped. The joints in use are. tongue-and-groove, or grooves cut in each side of the plank with a tongue driven separately.

What is known as the Wakefield pile (Fig. 17) consists of three planks bolted together to form tongue on one side and a groove on the other. This gives practically water-tight construction but as the planks are driven as a unit, the resistance to driving is increased. By careful selection and grading of the center plank, a good joint can be secured. Three advantages are claimed for this type of piling: namely (1) knots, cross grains, and other defects can be seen though it is unlikely that these defects would come at the same point of the pile; (2) there is no waste in forming the tongue and groove, and there is less tendency to buckle or warp before driving; (3) only one side of each pile is sharpened, the long edge being placed next to the last pile driven, which crowds the new pile against the old one and helps to make a tight joint.

66. Steel Sheet Piling-Steel sheet piling has rapidly come into extended use. While the first cost is higher than that of wood, its life is longer, and the pile is easier to drive. Also, whereas steel sheet piling may be used several times, timber piling will not survive much over 1 to 3 drivings.