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for decidedly beneficial results was found to be 3 days, while 7 days was about the maximum. The exposure of rosebuds to alternate carbon dioxide and air treatment (16 hours in carbon dioxide and 8 hours in air per day) was found to be as beneficial as the continuous treatment of the rosebuds. This method with some modifications has the possibility of a practicable application ( 5 ) . Discussion
Favorable effects of the carbon dioxide on some plant organs have been observed during these researches. The removal of the astringent flavor from the pear may be of practical value in rendering some varieties more desirable to the consumer as has been demonstrated with the persimmon. Bananas were retarded from ripening for a few days, which is similar to the effect of the gas on the apples studied by the English workers. Many flowers, especially those cut in the bud, were prolonged in life during storage
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by as little as 5 per cent carbon dioxide. The shipping of gladioli has been benefited by having the gas present to retard the opening of the buds. The varying response or tolerance of many kinds of plant organs to carbon dioxide during short periods of storage at many temperatures allows a broad field for further research. Acknowledgment
The writer is greatly indebted to the Dry-Ice Corporation of America for furnishing funds and for making helpful suggestions in carrying on this investigation. Literature Cited (1) Kidd, West, and Kidd, Dept. Sci. Ind. Research (Brit.), Food Invest. Bd. S p e c . Repf. 30 (1927). (2) Killeffer, IND. END.CHEM.,19, 192 (1927). (3) Killeffer, Ibid., 22, 140 (1930). (4) Sharp, Science, 69,278 (1929). ( 5 ) Thornton, A m . J . Botany, 17, 614 (1930).
Properties and Uses of Helium' W. E. Snyder and R. R. Bottoms THE HELIUMCOMPANY, LOUISVILLE, KY.
Helium is now available in commercial quantities in utilized in the extraction of E L I U M h a s some the United States, and there is a sufficient supply to helium from natural gas, as characteristic propmeet not only the needs of aeronautics, but for other will be explained later. erties which make it uses as well. This paper deals with someuses for helium valuable to industry. ProbUse of Helium in which are indicated by its physical and chemical propably the most outstanding of Aeronautics erties. these are its inertness and its Included in helium's characteristics are its chemical The outstanding use for low specific gravity. Helium inertness, low specific gravity, insolubility, high therhelium is in the field of aerois the only really inert gas mal conductivity, and low boiling point, indicating nautics and this use is based which is produced in anyuses in the fields of metallurgy, food preservation, heato n i t s non-inflammability thing like commercial quantiing and cooling, as a circulating medium in drying (chemical inertness) and its ties a t the present time. Its systems, and in grading and grinding of powdered malow specific g r a v i t y . The specific gravity is 0.138 as terials. It may also be used in combination with oxyGraf Zeppelin, by its recent compared with 1 for air. gen as an artificial atmosphere for use in deep-sea divlong trips and its continuous The solubility of helium in ing and caisson work and in the treatment of pulmoshort flights, h a s demonwater is 1.48 gaseous volumes nary and blood diseases. s t r a t e d the superiority of to 100 volumes of water at 0 " the airshb in long-distance C., while that of nitrogen is flying and its complete reliability. This- superiorzy is due 2.35 volumes, and of oxygen, 4.89 volumes. The thermal conductivity of helium is approximately six in part to the fact that the airship is not dependent on dytimes that of air. The chief inspector of the Aircraft Devel- namic lift of motors and wings; that it can safely "ride out" opment Company stated that when inside a ship last summer storms; and that, conversely to the airplane, an increase after it had been inflated with helium, the heat conductivity in size greatly increases payload capacity. The airship, as distinguished from the airplane, is a lighterof helium was so great that, although the outside temperature was between 80" and 90" F., the temperature inside than-air craft, which floats in the air by virtue of the fact felt nearer the freezing point. This property of helium may that a light gas displaces a heavier gas-namely, air. It is make it one of the most valuable of our industrial gases for use distinctly a displacement craft, in that its rising or lifting as a continuous circulating medium in heating and cooling power comes from the difference between the weight of the systems. It is the same quality that has developed the use air displaced and the weight of the lifting gas which displaces of hydrogen as a cooling means for electrical equipment. He- the air. Helium, by virtue of its own properties, has no lium for this purpose has the same advantage that it has in lift whatever, any more than a cork has lift, although a airship work-namely, complete inertness and lack of hazard. cork will rise in water. As a matter of fact, helium has a Surrounding this electrical equipment with hydrogen may dead weight equal to 11 pounds for each 1000 cubic feet. not be hazardous, but it is obvious that a non-flammable gas The weight of air under the same conditions is about 75 would be positively non-hazardous. pounds per 1000 cubic feet; therefore, the buoyant effect of The rate of effusion or diffusion of helium is approximately helium is roughly 65 pounds per 1000 cubic feet. three times as great as that of nitrogen. The new airship, ZRS-/,, being constructed for the Navy The melting point of helium is -271" C. This fact is Department by the Goodyear-Zeppelin Corporation, will have a capacity of 6,500,000 cubic feet of helium. The gross 1 Received August 9,1930. Presented before the Division of Industrial lift or buoyancy, of this quantity of helium will be approxiand Engineering Chemistry at the 80th Meeting of the American Chemical mately 422,000 pounds, or over 210 tons. The actual weight Society, Cincinnati, Ohio, September S to 12, 1930.
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of the helium necessary to inflate this ship will be about 71,000 pounds, or over 35 tons. If hydrogen were used in the same ship, the lift would be 455,000 pounds, and the weight of the hydrogen would be 33,000 pounds, or 17 tons. This would mean a gain in total lift by the use of hydrogen of from 7 to 8 per cent; but this advantage is usually short-lived because hydrogen diffuses through the fabric of airships about 50 per cent faster than helium, decreasing the lift. Even without its slower diffusion rate helium’s safety is the preeminent factor making it preferred over hydrogen. S C S I D U ~ L GASCS
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Experiments carried on t o date have shown that divers can work at a greater depth with more comfort and much shorter decompressing period when the helium-oxygen mixture is used as a breathing medium instead of air. The mixture prevents development of caisson disease, or “bends.” Considerable fundamental data must be accumulated before this use can be developed on a commercial scale, however. It has been shown that oxygen alone will not support life. Even when mixed with other gases, with one exception, the artificial atmosphere created usually kills. The notable exception is a mixture of oxygen and helium. Life thrives in this mixture. This indicates an important humanitarian and economic use in the treatment of pulmonary and blood diseases and in crises where today oxygen is administered alone to sustain vitality. Uses in Metallurgy
Another combination of properties of helium may find use in the metallurgical field. They are its chemical inertness, high thermal conductivity, and its insolubility in certain metals, either solid or molten. This combination of properties indicates that helium might be used when melting metals to prevent the formation of blow-holes in castings or “pipes” in steel ingots, or displacement of dissolved gases. Bright metal parts have been successfully annealed in an atmosphere of helium without tarnishing. As yet this has been done only on a laboratory scale. Heating and Refrigeration
/’o CoMPfarSsMa Figure 1-Schematic Diagram of H e l i u m Extraction Process
The economic features involved in any comparison between hydrogen and helium for airship use have been discussed considerably among airship men, and it has been quite definitely concluded that helium is more economical than hydrogen. This is largely due to the fact that helium can be repurified when dilution with air has decreased the lift or buoyancy to a point where economical operation demands it. Furthermore, the insurance companies in this country will insure helium-filled airships a t a reasonable rate, but will not insure hydrogen-filled airships. Uses Based on Insolubility Another interesting property that indicates a use for helium is its insolubility. As mentioned above, the solubility of helium in water at 0” C. is approximately half that of nitrogen, while the rate of effusion and diffusion is more than three times that of nitrogen. Elihu Thompson first suggested that this property might make a mixture of helium and oxygen a desirable atmosphere for caissons or deep-sea diving. The Bureau of Mines at Pittsburgh has carried on a series of investigations to establish the feasibility of such a mixture for this work, and the Helium Company has established a fellowship at Purdue University for further study of this and relative matters.3 2 This work is being undertaken under the direction of R. B. Moore, the “father of helium in America.” under whom it was the author’s privilege to work in the early days of the helium development.
Another use of helium which is indicated by its high heat conductivity is in the field of heating and refrigeration. H e lium has been suggested as a medium for circulation in domestic heating systems for house heating in the winter and for space refrigeration in the summer. It has also been suggested that the living quarters aboard aircraft, both dirigibles and airplanes, might be heated by means of the circulation of helium in a closed system, first heating the helium by means of exhaust from the engines, and then circulating the hot helium through radiators in the living quarters. Such an arrangement would eliminate the danger due to leakage of exhaust gases into the living quarters in cases where engine exhaust is used for this purpose. Grinding and Grading of Powdered Materials
The combination of chemical inertness, high heat conductivity, and low specific gravitJy should make helium valuable in the grinding and grading of powdered materials, especially those which are inflammable. The greatest value would be in connection with the materials which are to be finely ground-say, 200 mesh or finer, By circulating the helium in a closed cycle the material could be picked up as a dust. The lightness of the helium would permit the heavy particles to drop out and leave the finer ones to be carried over to the separating equipment. Helium as a Drying Agent
The property of chemical inertness, coupled with the high heat conductivity, makes helium of special interest as a circulating medium for drying many substances now dried by other means. Among the products that might be dried to advantage by helium are the following: albumin, casein, cereals, milk powders, electrical equipment and insulating materials, explosives, fruits and vegetables, gelatin and glue, meats and fish, organic extracts, rubber, soaps, starch, sugar, yeast; as well as all kinds of delicate organic and inorganic materials that would be adversely affected by high tempera-
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ture or contact with an active gas such as air, steam, carbon dioxide, etc. The high heat conductivity gives to the use of helium as a circulating medium for drying a decided advantage over the use of a vacuum. The heat conductivity of a vacuum is so small that the material will reach a low temperature, owing to the vaporization of the moisture, and the drying operation is very slow. This drop in temperature cannot be counteracted even by circulating steam or water in the chamber. I n drying iT-ith helium not only is there a much greater heat transfer, but the temperature can be kept uniform. It is a well-known physical fact that liquids i n c o n t a c t with fixed gases h a v e a h i g h e r vapor p r e s s u r e t h a n when in c o n t a c t o n l y with their own vapor (1). As a result material can be dried more quickly when in contact with fixed gases than in a vacuum, if the gases are kept in circulation to remove the vapor.
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liquid is drawn out through valve 2 and passes out around a high-pressure pot and interchanger, out through a line marked “residual gas,” The crude helium, containing from 65 to 7 5 per cent helium, is taken off from the top of the pot, goes into compressors, and is recompressed to 2000 pounds, then returns through an interchanger into the side of a high-pressure pot. The impurities are liquefied and drawn off, through valve 3, into the low-pressure pot, where any dissolved helium is released a t the lower pressure and recycled with the crude helium. The purified helium goes out through the line marked ‘‘pure helium” to storage or containers for shipment. The pressure on this pot is maintained bv an automatic backpressure regulator, 4. In this process no external refrigeration is required, as all the refrigeration is obtained as a r e s u l t of d r o p p i n g the pressure of the raw gas. At n o r m a l a t m o s pheric temperatures and below, all so-called permanent gases that condense to liquids a t atmospheric pressure above -200” C. possess a greater amount of inHelium as a Food Preservative ternal energy a t low pressures than a t high press u r e s . This difference Recent work has inin heat content of gases dicated that helium may with difference in preshave a definite use in sure is due to the lateniathe preservation of food. ing of heat in the separaBy the use of helium, tions of the molecules of other gases, such as oxyt h e gas against t h e gen, nitrogen, and carFigure 2-Portable Helium Repurification Plant mutual attractive forces bon dioxide, a r e comof the molecules and to p l e t e l y excluded from contact with the food, and this has a tendency to pre- the slight separation of the atoms within the individual vent the growth of bacteria and the oxidation of food molecules. This is the first example known in which a gas liquefaction products, which usually causes rancidity. This laboratory has carried out some experiments which indicate that process has been carried out through auto-refrigeration in such use is entirely feasible. Orange juice kept in sealed which the gaseous constituents all pass through a complete containers for six months appeared to be as fresh as in the liquid phase. Other processes depend on external refrigeraoriginal form. No experiments have been made to dcter- tion, or throttle the constituents, all of which have not been mine whether helium might be used in the preservation of reduced to the liquid phase. meat, but it is not at all improbable. A sponge cake was Portable Repurification Plant baked in Louisville last summer and half of it was placed in an atmosphere of helium and sealed to exclude air. The The same property of helium has been taken advantage of other half was left in ordinary atmosphere. After two months the part which was sealed in helium was found to be as fresh in the design of a portable repurification plant for the Goodas when it came from the baker. Of course, the other half year-Zeppelin Corporation (Figure 2). The design of this plant follows along the original design by Harvey N. Davis, was completely spoiled. president of Stevens Institute of Technology, with minor change. This plant has been delivered and is in use as an acExtraction of Helium from Natural Gas cessory to Goodyear’s airship operations a t Akron. It is One other property of helium has been utilized in its ex- mobile enough to traverse any terrain that a motor can netraction from the natural gases-that is, its low boiling gotiate. I t s rate of purification is 1500 cubic feet an hour point. The simple description of the operation of one of the and one of its advantages is that it can be drawn to the side of an airship, withdrawing and repurifying the helium and disHelium Company’s extraction plants follows. Figure 1 gives a schematic diagram of the helium column. charging it back into empty ballonets within the ship’s The raw gas containing helium, after having the carbon diox- main bag a t the desired pressure. The mobility of other soide and moisture removed, is compressed to from 700 to 2000 called portable repurification plants is limited, because they pounds, and comes into the column through the entry marked are mounted on railroad carriages. “raw gas.” After going through an interchanger, it is exLiterature Cited panded through a throttle valve, 1, into a low-pressure pot, which operates a t from 75 to 150 pounds. From this pot a ( I ) Euken, Jette, and Lahfer, “Fundamentals of Physical Chemistry,’ good part of the undesirable constituents are liquefied. This p 119.
