EVAPORATION OF FRUIT. 405 



perature is 59 F. it absorbs J^ part of its weight of water, 86 

 F. J-o P art , 113 F - TO Part, 140 F. ^ part, 167 F. J part, 

 194 F. f part, and 221 F. its own weight, which is nearly 

 equal to one pound of w r ater to every J cubic foot of air. 



The fruit would evidently never become dry if the air loaded 

 with such moisture remained stationary, but set it in motion with 

 a velocity of 880 feet per minute, which is equal to 20 miles per 

 hour, and the cause of the rapid drying, or, in other words, of 

 the withdrawal of water, becomes apparent. Xow if we figure 

 to ourselves an apparatus of 225 cubic feet content, the air heated 

 to 212 F. in it contains, according to the above statement, 60 

 pounds of water, 50 pounds of which have been withdrawn from 

 the fruit, while the remaining 10 pounds were contained in the 

 air prior to its entrance into the apparatus, because its tempera- 

 ture is supposed to be 62.5 F. With sufficient circulation to 

 empty the apparatus every 20 minutes, 150 pounds of water will 

 each hour be carried from a quantity of fruit supposed to amount 

 to 800 pounds. Hence, in 5 hours, the time generally required, 

 for apples, 750 pounds of moisture could be removed if present. 



Moreover, reference to a drying apparatus is not required to 

 prove that heat alone does not suffice for drying. Is it not the 

 wind which dries up the puddles after a rain more quickly than 

 the hottest rays of the sun? The sun alone would effect nothing 

 else but envelop the moist earth in a dense mantle of vapor de- 

 structive to both men and animals. Thus in the drying appa- 

 ratus also it is rather the current of air which dries than the heat, 

 but, of course, both must work in conjunction. The rapidity of 

 the process prevents decay, and causes the color and aroma of 

 the fresh fruit to be retained. The greater advantage of this 

 rapidity consists, however, in the conversion of a considerable 

 quantity of starch into sugar, which in sweet fruits, such as 

 peaches, is sometimes formed in such abundance as to appear in 

 small congealed drops upon the surface. 



From the preceding it will also be readily understood why 

 drying in the sun or in the oven must yield unsatisfactory re- 

 sults. Even with favorable weather the process lasts about 14 

 days ; during this long time a fermentation sets in which par- 

 tially destroys the content of sugar, and essentially changes the 

 color and taste in an unfavorable direction. Such fruit when 



