4 CIRCULAR 76 5, U. S. DEPARTMENT OF AGRICULTURE 



of storage in an atmosphere containing 3.25 p. p. m. of ozone for 

 several hours per day, but none of them occurred in an atmosphere 

 containing 1.95 p. p. m. during 5 months of storage. 



Ozone appeared to have no effect on major physiological activities 

 of apples. This was demonstrated by the fact that no difference 

 could be found in the maturity of ozonized and nonozonized fruit 

 at any time during the storage period as measured by pressure tests, 

 composition of internal atmosphere, pH, and total acidity. 



The experimental data upon which these conclusions are based are 

 given in the following pages. 



MATERIALS AND METHODS 

 Storage Facilities and Fruit 



During the 1941-42 and 1942-43 storage seasons the effects of ozone 

 on the keeping qualities of apples were studied. Each of the two 

 storage rooms used had a capacity of 825 cubic feet, or approximately 

 half a carload of apples; in both seasons both rooms were filled to 

 capacity. During storage the temperature was 31° F. and the relative 

 humidity was approximately 88 percent. One room had a normal 

 storage atmosphere and the other an ozonized atmosphere ; the air in 

 both rooms was continuously circulated by 16-inch electric fans. The 

 ozonizer was operated daily except Sundays beginning October 31. 

 During 1941-42 it was operated only 1 to 2 hours daily, since it had 

 been reported (2Jf) that ozone was as effective when applied once daily 

 as when applied continuously ; but during 1942-43 it was run about 8 

 hours daily. The average ozone concentration reached during the first 

 season was 1.95 p. p. m. by volume. Because of its failure to reduce 

 decay, the ozone concentration was increased during 1942-43 ; and the 

 average of the daily concentrations measured after the ozone had 

 reached a constant level was 3.25 p. p. m. 



The apple varieties stored were Delicious, Golden Delicious, York 

 Imperial, Rome Beauty, Winesap, and Arkansas. The special lots for 

 periodical examination and for inoculation were composed of carefully 

 selected fruit. Duplicate lots were placed in each storage room. The 

 rest of each room was filled with orchard-run fruit. 



Ozonizer 



The ozone generator, which was constructed and assembled in the 

 laboratory, was essentially like that described by Goss and Phillips 

 (13). It consisted of three Berthelot tubes made of Pyrex tubing 

 (fig. 1). The tubes were partially immersed in water in a large 

 battery jar, 9 by 12 by 17 inches; they were connected in series by 

 means of oil seals (fig. 2). Sufficient alcohol was added to the water 

 to prevent freezing when the ozonizer was used in storage rooms held 

 at 31° F. A coil of copper tubing was fitted inside the bottom of the 

 jar, the two ends of the tubing being bent upright to extend parallel 

 above the top. This copper tubing served as one electrical terminal. 

 A cover of asbestos fiberboard was fitted over the top of the jar to 

 accommodate and hold in place the ozonizing tubes and the copper 

 tubing. 



