From the helmet, in front, hangs a pair of false lungs, or large rubber sacks, protected by a leather apron; and on the back, held by straps over the shoulders and supported by plates fitting closely to the small of the back, hangs a heavy knapsack weighing about forty pounds. This knapsack consists of two steel cylinders, each one containing pure oxygen compressed to one hundred and thirty atmospheres, sufficient to support life for one hour, the two together being sufficient for two hours. Above the oxygen cylinders are two cartridges, or cans, containing loose crystals of hydrate of potassium sufficient to absorb two hours' exhalation of carbonic acid gas. With the helmet these cartridges and the oxygen cylinders are connected in a continuous circuit, and as soon as the oxygen is turned on there is a flow up from the oxygen cylinders by a tube under the right arm to the helmet, and down under the left arm to the cartridges, and through them again to the tube at the oxygen valve.

Upon adjusting the helmet, the wearer takes several large breaths of pure air, which he exhales into the false lungs on his chest, and immediately shuts the mouth valve. At the same instant, with his right hand behind his back, he turns on the oxygen, and this, regulated by valves to an even feed to last for exactly two hours, forces itself up the tube into the helmet, and by its pressure and reverse suction, draws down through the other tube and through the cans of potassium hydrate the exhaled breath. Air being a mixture of pure nitrogen and pure oxygen, the oxygen cylinders furnish one necessary element. The second - the nitrogen already exists in the several breaths that the man has taken into the false lungs, for the nitrogen atoms are indestructible, and, mixed with oxygen, can be used indefinitely. Passing through the potassium-hydrate cylinders, the carbonic acid gas is entirely absorbed, leaving the free nitrogen atoms to unite with the oxygen below; and so for two hours, a steady stream of air passes up through the right-hand tube, and for two hours the cans of potassium hydrate absorb the impurities exhaled, and pass on the nitrogen atoms to unite with the fresh oxygen ever flowing up from the cylinders.

In order that the helmet-men might keep exact account of the

amount of oxygen used, there was a clock fastened to the knapsack. When the helmet was adjusted and the oxygen turned on, the hand of the clock pointed to two hours, and as the pressure in the cylinders was reduced, the hand slid back to one hour, thirty minutes, fifteen, and finally zero, when it would be necessary to open the valves and breathe the outer air or suffocate. We could not see the clocks on our own knapsacks, as they were behind our backs, and so every fifteen minutes or so we would gather in the gas-filled tunnels, and with our electric torches read the minutes remaining on each other's clocks. Thirty minutes left meant a start for top, even if we were near the hoist. We could take no chances. Unconscious men are hard to move, especially when one's own air has almost gone.

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A MECHANICAL DISH-WASHER 1

A SIMPLE type of dish-washing machine has been invented and placed on the market. This machine consists of a cylindrical metal tank finished in aluminum and mounted on four stout legs with casters to permit easy rolling about the kitchen or from kitchen to china closet. A pump placed in the centre of the tank, and operated by the lever at the top of the machine, works in such a way as to throw the hot water in a strong stream against and among the dishes. China is placed at the bottom of the tank, all pieces being turned toward the centre and arranged to drain easily, while glass and silverware are placed in a wire basket near the top of the tank. After all pieces are in place, boiling water is poured into the tank and sprinkled with soap powder, the lid is closed, and the pump handle is worked for one or two minutes. The suds are then drawn off through a faucet at the bottom, scalding rinse water is poured into the tank, and the pumping operation is repeated. The dishes are sterilized by the hot water and are so hot when they come from the machine that they dry quickly.

1 From Popular Mechanics, October, 1913.

HOW THE PANAMA LOCKS ARE OPERATED 1

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THE mechanism which will operate the ponderous locks at Gatun, Miraflores, and Pedro Miguel in the Panama Canal is quite unlike anything used elsewhere in the world. Heretofore it has been the practice to distribute a large operating force practically along the full length of the locks in a canal. Such a force is difficult to coördinate into an efficient operating system. Moreover, the great size of the Panama locks made it highly desirable that all operations should be centralized. The flight of locks at Gatun, for example, extends over a distance of six thousand one hundred and fifty-two feet, and the principal operating machines are distributed over a distance of four thousand one hundred and fifteen feet.

The Isthmian Canal Commission decided that the locks must be electrically controlled from some central station in each case, because thus the number of operators, the operating expense, and the liability to accident could be reduced. Great electrical control-boards have therefore been especially invented which are installed at Gatun, Miraflores, and Pedro Miguel control-boards which are so ingeniously conceived and constructed that a single man, who need never see the ships which are passing through the canal, opens and closes lock gates weighing many tons and governs the course of thousands and thousands of gallons of water.

Before we can understand how this is done, we must explain how the locks themselves are constructed and what is the character of the lock machinery to be controlled. The lock chambers are one thousand feet long. At each end of a lock chamber, so-called mitering gates are to be found, which consist of two massive leaves pivoted on the lock walls and operating independently of each other. Immediately beyond each pair of mitering gates at each end of a lock chamber a duplicate pair of mitering gates is to be found. These are guard gates. Lastly, still other mitering gates open and close within the lock

1 From Scientific American, March 7, 1914. Reprinted by permission.

chamber itself. These, which are called intermediate mitering gates, are used to divide the one-thousand-foot locks into smaller compartments when vessels of short length are to be handled. Thus, much water is saved. All the mitering gates, when closed, are clamped tightly together by a device called a miter forcing machine.

In front of all the mitering gates which are exposed to the upper lock level and also in front of the guard gates at the lower end are chain fenders. These chains are taut when the gates behind are closed and are lowered when the gates are opened for the passing of a ship. The chains are raised and lowered by a method similar to that followed in hydraulic elevators, with the additional feature that if a ship approaches the gate at a dangerous speed and runs into the chains, the chain is paid out in such a way as to stop the ship gradually before it reaches the gates. Two motors lower the chains for the passage of a vessel and raise it again after the vessel has passed. One motor drives the main pump supply water under pressure, and the other operates a valve which controls the direction of movement of the chain. These two operations are combined in one, each motor being stopped automatically by a limit switch when the motor has performed its function.

The locks are filled and emptied by three culverts, one in the middle wall and one in each side wall. The flow of water is controlled by what are known as rising stem valves. These valves are located in the culverts at points opposite each end of each lock, so that the culvert can be shut off at any desired point for filling a lock with water from above, or upstream, or for emptying it by allowing it to flow out and down to the next lock. Lateral culverts conduct the water from the main culverts under the lock chambers and up through openings in the lock floors.

The rising stem valves are installed in pairs, and each pair is a duplicate. Moreover, each culvert is divided into two parallel halves at these valves by a vertical wall. This arrangement reduces the size of each valve, so that it may be more easily operated. Even then, each valve measures eight by eighteen feet and is raised and lowered by a forty horse-power

motor requiring one minute for complete closing. One pair of duplicates is left open as a guard or reverse pair; the other pair is used for operating, so that in case of an obstruction in the culvert or of an accident to the machinery, the duplicate pair can be used.

At the upper ends of the culverts at the side walls, the duplication is accomplished by three valves in parallel, called the guard valves. Their service is exactly similar to that of the rising stem valves, except that three valves in parallel in this case must conform with the same laws as the two in parallel in the other case.

The culvert in the middle wall must serve the locks on both sides, and to control this feature cylindrical valves are placed in the lateral culverts that branch out on each side. There are ten of these on each side of the culvert at each lock.

At the upper end of each set of locks there are two valves in the side walls for regulating the height of water between the upper gates and upper guard gates, as it is desired to maintain the level of the water between these gates at an elevation intermediate between that of the lake above and that of the upper lock when the upper lock is not at the same level as the lakes. These valves are called the auxiliary culvert valves.

To give an idea of the number and sizes of the motors to be controlled in operating the lock machinery it may be mentioned that each miter gate leaf is moved by a twenty-five horse-power motor. There are forty such motors at Gatun, twenty-four at Pedro Miguel, twenty-eight at Miraflores, a total of ninetytwo, with an aggregate horse-power of twenty-three hundred. Each miter-gate forcing machine is worked by a seven horsepower motor. Of these motors there are twenty at Gatun, twelve at Pedro Miguel, fourteen at Miraflores, a total of fortysix, with an aggregate horse-power of three hundred and twentytwo. So, at Gatun, Pedro Miguel, and Miraflores there are in all forty-eight motors of seventy horse-power each, which work the main pumps of the fender chains and which have an aggregate horse-power of thirty-three hundred and sixty; fortyeight motors of One-half horse-power each for operating the

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