8 CIRCULAR 2 7 8, U.S. DEPARTMENT OF AGRICULTURE 



and 8 tenths (to the nearest thousand) of the figure for 10 days. 

 The specific heat has been calculated by the formula $=0,008 

 a +0.20 in which S signifies the specific heat of a substance contain- 

 ing a percent of water ; 0.2 is the value which has been assumed to 

 represent the specific heat of the solid constituents of the substance 

 in question (25). 



Column 1 of table 2 shows the kind and variety of fruit and col- 

 umn 2 the temperature of the fruit at the time cooling starts, in a 

 room held at 32° F. The next column shows the amount of heat 

 evolved by respiration if the fruit reaches 35° at the end of 3 days. 

 The next 5 columns show the amount of heat if cooling to 35° re- 

 quires 4, 5, 6, 8, or 10 days, respectively. The last column is the 

 sensible heat (obtained by multiplying the specific heat of the fruit 

 by the difference between initial and final temperatures and this 

 result by the number of pounds in a ton). " For any one kind of 

 fruit at a given initial temperature, this figure is assumed to be the 

 same for all the cooling periods included in the table. 



The values given in table 2 are only approximate. The two as- 

 sumptions that have been made, namely, (1) that the heat of respira- 

 tion is produced only by the oxidation of a hexose sugar and can be 

 computed from observed amounts of carbon dioxide produced, and 

 (2) that the rate of temperature drop is always proportional to the 

 difference between fruit temperature and room temperature, prob- 

 ably lead to fairly accurate results; but since only a few direct 

 measurements of the heat produced by fruits and vegetables have 

 been made, it is not known just how close the approximation is. 

 The figures are presented to help cold-storage-plant operators esti- 

 mate the quantity of refrigeration required for cooling the fruits 

 named, and under the various conditions given. As an example of 

 how they can be used, the following calculation may be of interest : 

 A ton of Bartlett pears cooling from 70° to 35° F. in 10 days in a 

 32° room is shown to be capable of producing about 51,000 B.t.u. 

 Its sensible heat at 70° (35 degrees above its final temperature) is 

 61,000 B.t.u. The sum of the two is 115,000 B.t.u. If this be multi- 

 plied by the capacity of the room in tons of fruit, say 600 (the 

 capacity of some of the commercial cold-storage rooms in the United 

 States), and divided by 288,000 (the number of B.t.u. in a ton of 

 refrigeration), the quotient 239 is obtained; this is approximately 

 the number of tons of refrigeration required to cool 600 tons of 

 Bartlett pears to 35° in 10 days, under the conditions specified. The 

 corresponding figure for T\ r inesap apples is 177 and for Grimes 

 Golden apples, 200. 



EFFECT OF COLD STORAGE ON SUBSEQUENT BEHAVIOR OF FRUITS AND 



VEGETABLES 



The belief is rather common among those concerned with the mar- 

 keting of fresh fruits and vegetables that commodities of this kind 

 that have been in cold storage deteriorate more rapidly after removal 

 from the low temperature than if they had been held at ordinary 

 temperatures. It is difficult, however, to find a basis for judging 

 whether or not they actually do so because there is no means known 



