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CHANNELING THE LOCK FLOORS In 1907 the Isthmian Canal Commission purchased twenty-four Sullivan channeling machines, some furnished with boilers for operation by steam, but the majority supplied with air reheaters to render their operation by compressed air as economical as possible. The use of stone channeling machines in engineering work dates from 1892, in the construction of the Chicago main drainage canal. In this enterprise, fifteen miles of canal had to be cut through solid rock. The advantages of a channeled wall over a blasted wall are numerous; the straight, smooth, solid cut made by the channeler, avoids any necessity of either trimming or filling to the engineer's line, the walls left by the channeler remain as solid as the rock itself, not weakened or shattered by explosives, and retaining walls to prevent rock falls or slips are obviated.

Another important advantage secured by channeling consists in the fact that the rock ground or structures adjoining the channeled walls are not disturbed or shattered, and it was in this connection that the channelers found their principal use on the Panama Canal. It had been planned at first to channel the Culebra division from end to end. This idea was abandoned, however, and the use of the machines was restricted to the sites for the locks.

In

The total amount of channeling performed in the locks was about three-quarters of a million feet, and included, in addition to the lock floor work, the cutting of trenches beneath the curtain walls and across the site of the dam at Gatun. these trenches, cut-off walls were built to divert the underground water, the presence of which was endangering the foundations of the locks and dam. In this case, also, it was of importance that adjoining ground should not be disturbed by blasting that might affect the stability of the foundations for the great concrete walls.

The design of the Sullivan channelers is

engines, the chopping engine and the feed engine, which drives the machine back and forward along the track through worm shafts and gearing. The feed engine also controls the power feed and hoist of the chopping engine. The valve motion is such that the operation of the machine, as to kind of blow and speed, may be modified to secure the best results for any stone and any operating conditions. Special valves in the exhaust ports permit cushioning of the blow, thus preventing damage to the front head, in case a mud seam or other irregularity in the rock is encountered. This was particularly valuable in the broken formation at Panama.

The twenty-four Sullivan channelers were the only channeling machines used on the canal.

The company also supplied much of the equipment for the diamond drilling in testing the location of the canal and the locks and dams.

The record for the number of a particular make of drill on the Panama Canal work belongs to the Star Drilling Machine Company of Akron, Ohio, which maintains branch plants at Portland, Oregon, and Chanute, Kansas.

This company furnished 214 drilling machines for blast hole and other work on the canal, and these figured importantly in the rapid and economical removal of the vast tonnages of rock and earth with which the canal engineers were confronted.

The Star Company makes a specialty of portable drills, and these in various forms were so widely used in the canal's construction that the company made the poetical boast that "Of a truth have the Stars lit the way 'cross Panama."

This form of drill is variously used for blast holes, well drilling, copper mine prospecting and many other forms of drilling. Gasoline, steam or electric power is used in their operation, the steam operated machines being generally used where coal or wood is easily accessible, and gasoline where the ordinary forms of fuel is scanty.

Where electric power is available, the machines are equipped for either direct or alternating current.

One of the advantages which led to the great number of these drills at the canal was the ease with which they could be set up or moved. The entire machine, including the engine and boiler, is compactly mounted on wheels, the traction style machines propelling themselves from place to place with their own power, while the others are easily hauled. The traction machines are powerfully back-geared for hill climbing and with high speed for fast traveling on free roads.

Other types of rock drills used on the canal in large numbers were the improved drills both of steam and air power, manufactured by the Wood Drill Works of Paterson, N. J. This company also furnished its heavy type bronze hose couplings in great numbers.

The Wood drills were used in the construction of the Miraflores lock chamber, in the Culebra Cut, and in getting out trap rock at Porto Bello for the Gatun locks. For these operations, this type of drill was selected after six months of competitive tests, the selection being based on quantity of work performed, long life of the machines, and ease of operation.

The manufacturers of these drills were the first to use vanadium tungsten iron in the construction of their drills, and their plant is devoted exclusively to the manufacture of drills.

The climatic conditions at the Canal Zone had no effect on these drills, it being claimed for them that they work equally well in either tropical or frigid climates. Simplicity and solidity of construction was one of their features, the motto of their manufacturers being that in the canal work they could be "cleaned up with a sledge hammer," 'wiped off with a scoop shovel" and be ready to continue operations.

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The drills, great and small, used to such large extent on the canal, and which were so large a factor in the rapid excavation, demonstrate that the United States leads

the world in this class of machinery. These busy machines, which paved the way not only for the water channel, but for the lock emplacements and other great features of the canal's construction, will remain among the first of the industrial implements and products which aided the directing minds of the work to bring it to rapid and successful completion.

EXPLOSIVES ON THE PANAMA CANAL

The casual visitor to the canal during its construction had a good opportunity to see in operation the powerful allies which man now has at his command, which make possible the accomplishment of such magnificent engineering projects. He saw the mighty steam shovels eating into the cut like so many living giants, the myriads of locomotives hauling away to the dumps what was once a part of the backbone of two continents, and the great cranes so gently and so easily lifting into place the massive sections of locks.

And then he met the blaster out on other parts of the work handling the mightiest of them all, the insignificant looking little rolls of yellow paper about one and onequarter inches in diameter and eight inches long, that made possible the work of all the other giants. For the most powerful steam shovel cannot dig, nor the greatest locomotive haul, solid rock.

The thoughtful person is therefore led to wonder what were the successive steps which have placed at man's command this greatest of all forces, lying so docile in the hand of the powderman; now held together by a couple of turns of waxed paper, yet which upon his demand exerts force of more than 500,000 pounds per square inch, resistless in its force, supreme in its conquering power.

The history of the successive steps which have given us this potent agent, dynamite, without which so many of the greatest engineering projects of to-day would be impossible, is however, unnecessary here. It will be sufficient to sketch briefly what dynamite really is, and to give a short

account of how that which was used in digging the Panama Canal was supplied.

The explosive basis of all dynamite is nitroglycerin. Everybody is familiar with ordinary glycerin as obtained from the drug store. If glycerin is treated under proper conditions with strong nitric acid, assisted by the presence of sulphuric acid, it is converted into nitroglycerin. The latter differs from glycerin not only in having explosive properties, but unlike glycerin it is almost insoluble in water, so that all traces of acid can readily be washed out, leaving the pure nitroglycerin. The chemical action which occurs is similar to that when nitric acid acts upon potash, converting it into potassium nitrate or saltpetre. The explosive properties result because the glycerin, a combustible, has had introduced into its chemical structure groups of atoms containing sufficient available oxygen to support the combustion, independent of air. The same group is introduced into potash when we convert it into saltpetre with nitric acid, and the only reason why saltpetre is not an explosive is because, while the oxygen is there, the combustion is not. By mixing a combustible with it—sulphur and charcoal, for instance we obtain an explosive, blasting powder.

Nitroglycerin itself is not very well adapted to blasting, for several reasons. Being a liquid, there are many situations constantly arising in blasting operations where it would be difficult or impossible to load it. Then again, it is very sensitive to concussion or friction, which makes it unsafe to handle or transport. These and other conditions finally led to its general applications in the form of dynamite, which in spite of the terror which the name inspires in the mind of the uninitiated, is by all odds, one of the safest of explosives. For, in an explosive, great strength is a measure of efficiency and not of danger; while on the other hand a comparatively weak explosive may be over-sensitive, unstable, and erratic in its behavior, and therefore dangerous.

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The first dynamite consisted merely of a very porous variety of earth (Kieselguhr) saturated with nitroglycerin, and its explosive qualities were due entirely to the latter. While this immediately produced a practical blasting explosive of about the consistency of and closely resembling brown sugar, which could be packed into cartridges and safely transported and handled, it is a kind of dynamite that is very little used in this country to-day. Here we prefer to use, instead of inert earth, an absorbent which is of itself an explosive, so that when fired we obtain the effects of two explosives working together. So we use for our absorbent a mixture of wood pulp and saltpetre or its equivalent, which forms a very good absorbent, and a mixture which also explodes with about the force of blasting powder under the influence of the heat from nitroglycerin.

A sixty per cent. strength dynamite made in this way is more than equal in strength to a seventy-five per cent. dynamite made with the inert earthy base. The gain in strength is not the only advantage, however, as the explosive base and the many modifications of it which are possible enable the chemist to control the quickness of the explosion as well as its strength, thus adapting different kinds of dynamite to practically every kind of work for which a blasting explosive is required.

Dynamite has many characteristics which give it an immense advantage over black powder, especially in a piece of work like the Panama Canal. Among the first of these is its resistance to water. While the Panama rock was soft enough to admit of using black powder-and some was used very successfully in the early part of the work, in holes that were chambered or enlarged at the bottom with dynamite so that they would hold enough of the black powder-the fact that black powder softens when wet into a black mud that will not explode forbids its use in a good deal of work where it would otherwise be effective. On the other hand, varieties of dynamite are sold by the du Pont Company which