INDUSTRIAL A N D ENGINEERING CHEMISTRY
1186
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Vol. 22, No. 11
Carbon Dioxide Storage of Fruits, Vegetables, and Flowers' Norwood C. Thornton Buvca TT~OMPSOU S v s n r u r s VOR PLANTRessnncx. Sxc., SOKXLUS. h-.Y.
Fruits and vegetables held in storage for 3 to 7 days withstood, without apparent injury, concentrations of carbon dioxide varying from 6 to S.5 per cent depending upon the kind and variety tested. The concentration of carbon dioxide tolerated by each fruit and vegetable was determined a t six storage temperatures varying from 32" to77'F. (O"to25"C.). The tolerance tocarbondioxide was influenced by the ripeness, firmness. and freshness of the plant organ. In general, the presence of an excess of moisture in the storage chamber is undesirable.
The carbon dioxide treatment prolonged the life of the flowers by retarding the opening of the buds. Rosebuds. when removed to warm air after a period of storage in 15 per cent carbon dioxide for 7 days a t 38' or 50°F. (3.3" to IO" C.), lasted as well asuntreated roses which had been in cold storage without carbon dioxide for 3 days. This treatment gave a possible gain of 4 days. Concentra. tions of carbon dioxide tolerated by flowers are given in Table I.
...... HE development of refrigeration with solid carbon dioxide, widely known under the trade-mark "DryIce," has required research into the application of gaseous carbon dioxide to make it practieal. The properties of carbon dioxide gas have rendered it vaiuable in many fields, though it has often been erroneously cited as an inert gas for the storage of perishable plant organs. The high latent heat of this gas discussed by Glleffer (O),its germicidal action on meat and fish reported hy Killeffer @),its preservative action on eggs invest,igatrd by Sharp (&), and its retarding effects on the natural ripening proresses of apples discovered by Kidd, West, and Iiidd (I), has each been applied in its Rppropriate field. The effect of carbon dioxide on
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frigeration has surpassed chemical or other treatments hecause of its retarding effert on respiration without great injury to the living plant organs. One notable exception has been the gas storage of app!es discovered by Kidd, West, and Kidd (I) when approximately 10 per cent concentration of the respired carbon dioxide was held in the atmosphere of
Fleure Z-Hesper3dln Crystals on Outer Membrane of Carpel Wall of Orange Held In SO Per Cent Carbon Dioxide f e r 7 Days st 50-P. (10- C.)
Figure I-Dutchesa Apples Held In Carbon Dioxide for 6 Daw s f 3 8 ' F . (3.3*C.> A , B . ron~cols:C . 26 per ant. no iniury or abnormal Bavar: D. 50 per cent, E . 70 per C-t, and P . 87 per eenf rholains injury, brolao about E O m end underskim. withsbnormal flavor.
respiring plant organs-fruits, vegetables, and flowers--stored for short periods is the subject of this preliminary study. The literature contains innumerable articles on the keeping of fruits, vegetables, and flowers in which many treatments have been proposed. With few exceptions controlled rea
Received August 18, 1930.
the storage room for many months. This treatment extended the storage life of apples by approximately 1.5 times that of the controls. They found that carbon dioxide storage a t 4F.5" F. (&lo C.) not only prolonged the storage life of apples, hut was as effective as cold storage in air st 34' F. (1.10 To handle Dry-Ice efficiently it became important tu determine the tolerance of various plant organs to artificially produced carbon dioxide atmospheres. The results show that some plant organs are improved for consumption by proper percentages of carbon dioxide, others have considerable tolerance of the gas, and only a few require that minimal amounts of it be present. These data are being applied to the design of practical refrigerator equipment for commercial use.
e.).
INDUSTRIAL A N D ENGINEEIMNG CHEMISTRY
November, 1930
Table I shows the tolerance of fruits, vegetahlen. and flowers to various concentrations of carbon dioxide during storage for definite periods at many temperatures. These data were
I 187
(0" or 3.3' C.) than a t 50' or GO" F. (loo or 15.6" (2.). Oranges, on the other hand, developed a bitter flavor during treatment with 64 per cent carbon dioxide that was the same at all temperatures of storage. The oranges injured by carbon dioxide contained large quantities of hesperidin crystals on theouter membranesof the carpel walls (Figure 2). Skin injury and tissue breakdown were very noticeable with the common or sweet orange (Citrus sinensis Osbeck), King orange (Citrus nobilis Lour), and tangerine (Citrus nobilis var. &lici&sa Swingle) held a t all temperatures in 80 to 100 per cent carbon dioxide during storage.
Vegetables
Held in Carbon M e r i d e for 7 Days *f 50' F. (10" C.) 4 , B . controls; C, 25 per cent. no injury: ,D!50 per cent, E, 70 per cent, and P , SO per cent, mqured. FiPure 3-Celery
obtained by determining the concentration of carbon dioxide in mixture with normal air that caused a change in appearance, odor, or taste of the plant organ under observation. The fruits, vegetables, and flowers used were obtained as fresh as possible and during storage were held in 35-liter tin cans (12*/4 by 18 inches) under conditions that would duplicate as nearly as possible the required shipping conditions from producer to consumer. The desired concentration of carbon dioxide was obtained by placing a weighed amount of Dry-Ice in the top of the can. The amount of Dry-Ice used was a t no time p e a t enough to cause injury by freezing of the plant organ. Analyses of the carbon dioxide content of the storage cans were made a t the beginning and a t the end of the test period. The cold-storage temperatures given in Table I were obtained in large refrigeration rooms. Since fruits, vegetables, and flowers responded differently to the carbon dioxide storage, they will be discussed separately.
The data in Table I show that freshly harvested vegetables varied considerably in response to the carbon dioxide treatment, some varieties being injured by relatively low concentrations while othem withstood high concentrations. Vegetables held in the injurious concentrations of carbon dioxide developed many darkened bruised-appearing are= that were watery. When removed to warm air, the injured portions of the vege-
the first to show injury. In tests? as might be exvected.
Control Carbon dioxide F14ure 4-The Effect of 5Resea Per Cent Carbon DIoaIde on Brlsrcliff Held 7 Day* *f 50' F.(iO' C.)
Fruits
The tolerance of fruits, except citrus, to carbon dioxide varied with the firmness and age of the plant organ. The noticeable changes in most fruits as a result of exposure to an injurious concentration of carbon di-
b y s longer in ripening than the controls. In every test the carbon dioxide Control 5% 10% 15% 20% 30% S-Effectiveness of Various Concentrations of Carbon Dioxide In Refardine fhs Bud removed the astringenent flavor from the Fipure Development a n d Dropping Of Petala of Talisman Roses H e l d for 7 Dam at SO'F. ( l O D C . ) pear and banana during storage. Citrus fruit withstood a relatively higli concentration of vegetable. Dry-surfaced vegetables were much more tolerant carbon dioxide without noticeable injury during or after to the carbon dioxide treatment than wet-surfaced vegetables. the st.orage period. Grapefruit was slightly altered in Flowers flavor by 50 per cent carbon dioxide, but higher concentrations brought about a bitter flavor tiiat was repugnant, being The carbon dioxide treatment of roses, gladioli, snapmore pronounced at storage temperatures of 32" or 38" F. dragons, and some \-aricties of carnations resulted in a re-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1188 T a b l e I-Effect
Vol. 22, No. 11
of V a r i o u s C o n c e n t r a t i o n s of C a r b o n Dioxide on Fruits, Vegetables, and Flowers S t o r e d a t Different T e m p e r a t u r e a
MATERIAL
PERIODTESTED,1929
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32'F. Apple: Dutchess Gravenstein Delicious McIntosh Banana Grapefruit: Walter5 Foster pink Thompson seedless Orange: King Common sweet Valencia Peach, Georgia Belle Pear:
Asparagus Bean, stringless Carrot (root) Cauliflower Celery Lettuce Mushroom Pea Radish (root) Rhubarb: Stalk D r y leaf Spinach Tomato Cosmos Dahlia: Jersey's Beauty Clarissa "Fern: " Aspidium spinulosum Asparagus plumosus Gladiolus Salmon pink Rose Dink Rose: Briarcliff Pierson Talisman Talisman Talisman Snapdragon ~
COz CONCENTRATION AT WHICH INJURY WAS OBSERVED AT:
COz CONCENTRATION AT WHICHNo INJURY WAS~OBSERVED AT: ~ A ~ 38'F.
50'F.
60'F.
70'F.
77'F
%
%
2 ° F 38'F.
50'F.
60'F.
%
70'F. 77'F.
Days
%
%
%
%
%.
%
%
6-7 7
25 46
25 30
0
a
a
(1
50 64
50 50
28 27
25 25
7
83
67
50
a
(1
78
70
26
6-7 7
48
25
25 a
65
50
33
25
50 25
40
February- April April April
7 7 7
25 50
25 50
25 50
25 50
50 65
50 65
50 65
50 65
April February-April April August-September
7 7 7
a
30 50 50 20
30
(I
50
50 50
27 64 63 30
52 64 63 30
52 64 63 20
30 643 6
62 28 25 50 50
49 28 25 50 50
28 25 50 50
3,0
3,0
August August-September January-March, OctoberNovember February, October-November February-May
4
January-March August-September April-June April May-June May-June Tune June January-March January-March February-April April-May June
7
June June January, March, and June August-September July-August September
7 7 4 4 4
7 3 7
3 3 5 7 7 7 4 4 7
5 5
September-October
50 50 20 42 10 15 25
80
80
80
(1
L1
a
0
50 25 6
2,7
2,7
2,7
70 30
6 15
6 15
G
10
50 20 10 25
50 20 10 25
50 20 6
July-August-September
(1
10 15 25 28 18 80
2,5
0
2 *5
2,s 25 0.
n
15 80 25
a
25
50 50 13 25
30 70
50 50 13 25 30 70
15
25 40 50
15 80
25
15 15
15 15 40 37 30
15 15 40 37 30 15
64
30 12
50
15 15
15 15
50
26
l,O
0
40
%
10
SO
2,s
4
2-3-7 2-3-7 2 3 7 4
0
80 25 25 7 15 19 50
4
July-December, incl.
50
25 10 15 25 28 18 80 25 25 7 15 19 50
7 5
July-August-September
50 10
33
%
G
18 50
0
20
25 20
25 20
20 20 48 45 40
20 20 48 45 40 25
Not determined.
tardation of the bud development, thus prolonging the life of the flower. Cosmos held in storage for 4 days with 15 per cent carbon dioxide did not lose petals so easily as the controls, whereas the Jersey's Beauty dahlia was seriously injured by the same concentration. Sweet peas, on the
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AND
vm.lil ' l t l l O N
3
5 per cent was found to be effective (Figure 4). When removed to warm air (75' F. or 23.9" C.) the controls usually lost petals very quickly while the treated buds opened slowly with good color and shape (Figure 5). Florists usually do not sell roses for home use that have been in the refrigeration case more than 3 days. Rosebuds similarly handled, except subjected to carbon dioxide treatment, remained in good condition for seven days. After 7-day treatment these roses lasted fully as long at room temperature as the untreated ones that had been removed from the usual storage a t the end of 3 days. Treatment of some varieties of roses (Table I) with 20 per cent carbon dioxide caused a browning of the outer three or four petals. These injured petals could be easily removed, a procedure which is in accord with the present commercial practices. The slightly injured buds opened in good condition when held in warm air. Higher concentrations of carbon dioxide caused bleaching, browning, and some stem injury to rosebuds. The Talisman variety withstood 30 per cent carbon dioxide for 7 days (Table I), but the higher concentrations inhibited bud development and also injured the petals. Storage periods of 3 to 7 days were found desirable for the continuous carbon dioxide treatment, since the buds after longer periods of exposure had a tendency to lose petals very quickly when removed to warm air. The shorter the period of treatment the less effective was the carbon dioxide on the buds unless the concentration was greatly increased as shown by Figure 6. The minimum period of treatment
November, 1930
I N D L S T R I A L A N D ENGINEERING CHEMISTRY
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
1189
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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