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the time they are filled until they are emptied at Lakehurst, is from ten to twenty per cent. It takes a crew of men about two days to unload a car of about 600 of these cylinders and prepare them for discharge after the carload is received at Lakehurst. Whereas with the Tank Car, one man in five minutes after the car arrives can be ready to supply twice as much Helium as contained in the 600 small cylinders. It was the realization of the inadequacy of these cylinders and the potential possibilities of the large storage cylinders, that led to the design of the Tank Car. This car consists of three large steel tanks, forty (40) feet long and four (4) feet nine (9) inches in diameter, mounted on a special railway truck. The cylinders are made of a special alloy steel, hollow forged from a solid billet to walls four (4) inches thick. After forging, the tube is machined inside and out to reduce the wall thickness to about two (2) inches, in order to reduce the weight of the total car to about 200,000 pounds. The cost of transportation will be cut down materially; a big saving in the cost of handling will be effected, and the loss in shipment of about ten to twenty per cent of the Helium will be eliminated as soon as an appropriation can be obtained to purchase enough of these cars to meet the requirements of the service. Due to the recent improvements in the production of Helium, it now costs more to handle and ship the gas than it does to produce it.

The Army and Navy have used the twenty-four (24) million cubic feet of Helium, which has been produced at the Helium Plant since it commenced operation in April, 1921, until July, 1925, in lighter-than-air ships, and the Navy could have used more if it had been available. As this activity increases, the demand for Helium will increase, reaching about twenty million cubic feet a year for both services in the near future. The inauguration of commercial airship transportation will double this demand, and after its practicability is definitely proven, this field will probably call for at least fifty

(50) million cubic feet a year. It is very much to the interest of the Navy to encourage this new enterprise, as the commercial air fleet of the future will be a very important adjunct in case of war, especially so as there will be ample trained pilots available and the ships will be filled with Helium. It is the production of the Helium for complete inflation that takes a long time and large production plants; the make-up Helium required to take care of operation losses is relatively small and a large fleet of airships can be maintained by the production of relatively small plants.

The Navy Department and the Bureau of Mines are now actively engaged in an extensive program of experiments with men using an artificial air composed of various mixtures of Helium and Oxygen as a substitute for normal air for use in diving, mining and tunnelling work. The preliminary results are very encouraging. Helium is without odor or taste, and has physical properties which promise to be of interest physiologically. The substitution of Helium for the nitrogen ordinarily present in the air we breathe has been found to result in an atmosphere which is as respirable as that provided by nature, and at the same time will reduce the hazard of caisson disease. The results obtained indicate that Helium not only has the advantage of being less soluble than nitrogen, but also has the advantage of diffusing more rapidly in the blood and other body fluids and tissues which results in rapid elimination of the gas from the tissues during decompression. So from a product developed as a war-time necessity there has been created a need for humanitarian purposes.

The writer has recommended to the Bureau of Engineering that experiments be conducted with Helium filled searchlights on account of the following properties of that gas: high thermal conductivity; low dielectro cohesion; inert, and will produce a yellowish light. Some experimental work has been done in the use of Helium in a closed system for cooling large electrical generators and motors, and as soon as Helium is

more plentiful its usefulness will increase rapidly. This should permit a large reduction in the amount of copper in the machines and increasing the load on the machines already built with a consequent increase in efficiency. Hydrogen is a little better suited for this purpose, but the danger of explosion is too great to permit its use.

The future supply of Helium for the various demands which will be made for it lies primarily with the great Petroleum Industry of this country, against which falls the necessity of discovering new Helium bearing natural gas fields, and conserving this gas in the ground until it is required to furnish the Helium which is contained therein. It is an economic impossibility to extract Helium and store it in containers. The only practical method of conserving this important gas is to leave it in the ground in its natural state until it is required for immediate use. The responsibility of the Petroleum Industry in this respect was laid before it at the general session of the American Petroleum Institute at Fort Worth, Texas, in December, 1924, by the Navy Department, and was given much consideration by that Institute.

At the present time there are six well defined areas at some distance apart which are developed as producing or potential natural gas fields, and sufficiently rich in Helium to warrant the commercial extraction thereof. The Government Helium Plant at Fort Worth is tapping one of these areas, and a second, located on Federal land, has been set aside as a reserve for National emergency. A third area is also on Federal land, but has not been withdrawn. That leaves three areas rich in Helium and not on Federal lands, which are already known, and are producing gas which is available for the extraction of Helium by commercial concerns. The Bureau of Aeronautics, through its Chief of Bureau, Rear Admiral W. A. Moffett, has already taken the stand that the commercial production of Helium is a necessity, and it will be encouraged by that Bureau. The Bill passed by the last session of Con

gress, which transferred the Helium activities from the Army and Navy Helium Board and the Navy Department, also specifically requires the Government to purchase Helium from private concerns as soon as they are in a position to furnish it at a cost comparable with what it costs the Government to produce it at the Fort Worth Plant. The future supply of Helium to the various consumers is, therefore, placed directly up to the great industrial organizations of this country.

STARTERS AND CONTROLLERS FOR NAVY D. C. MOTORS-TYPES AND PRINCIPLES OF

OPERATION.

By C. HUEY, CIVIL MEMBER.

All direct current motors in the Navy over one horsepower are required to be started by a current limiting device. This device is known as a "starter" or "controller." These terms, although descriptive in themselves, are often used synonomously and need therefore be defined.

STARTERS AND CONTROLLERS DEFINED.

A "starter" is a device for limiting the current until the speed of the motor has increased to such a value that the motor can safely be connected directly to the line voltage. The primary function of the "starter" is to get the motor "on the line." The addition of protective or safety devices such as an overload release, a no-voltage release, fuses, line switches, etc., does not change the correct application of the term "starter."

A "controller" is a device for starting, stopping and reversing, or controlling the speed of a motor. The primary function of the "controller" is to permit the change in direction of rotation of the motor, or to regulate or vary the speed of the motor other than that caused by the external load or electrical characteristics of the motor. The controller includes the functions of a starter, and the addition of protective devices does not change the application of the term "controller."

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