It has been objected that fruit can never dry in a heated atmosphere filled with 

 moisture. This objection is theoretical, not philosophical or real, when the 

 moist air is in motion, as our philosophies taught us years ago. 



Air at the freezing point, 32=. holds one 1 60th of its weight of water as vapor, 

 and its capacity for holding moisture is doubled with every 27° of temperature 

 above 32°, or the freezing point, so that at 59° of the thermometer the air will 

 absorb the 80th part of its weight; at 86^ the 40th; at 113° the 20th; at 140'' 

 loth; at 167'=', 5th; at 194°, die 2.5; and at 221'' F. the air will absorb almost 

 its own weight of moisture, or nearly one pound of water to every one sixth cubic 

 feet of air. Now it is evident that if this amount of moisture was contained in 

 the air at rest, the fruit would never dry. Hence the necessity of carn,-ing off 

 the moisture — -loaded air — as rapidly as possible by an active draft. 



Another fact that needs to enter into the account: evaporation takes place at 

 the surface of bodies, and is influenced not only by temperature and dr}'ness, 

 but by the stillness and density of the air in which the article to be dried is placed. 



If the air be heated and at rest, as in an air tight oven, fruit will not diy, 

 though the dr}- air will be loaded with moisture. Wind, air in motion, is neces- 

 sary to dry any substance, and more is due to the wind than to the sun in drying 

 the earth after a shower; so a current of heated dry air, constantly supplying the 

 place of the moisture charged air carried off b}- the draft, is the grand secret of 

 success in drying fruits. 



NATURE OF THE ALDEN EVAPORATING PROCESS, 



Pneumatic Evaporation as scientifically perfected by 'Sir. Alden, is essentially 

 a novel art ; not onlv distinct from, but opposite to desiccation, so called, in 

 chemical principles and practical results. It is a process which not only fore- 

 stalls decay, and which not only seizes and perpetuates the fresh flavor, color 

 and texture of the article (animal or vegetable) subjected to it, but which, in 

 doing these things, at the same time carries out the organic process of ripening 

 itself to an artificial perfection, on the same principles incompletely used by 

 Nature, and with a correspondent increase of the nutritive product. 



The means employed by ]\Ir. Alden to produce these results are threefold — 

 namely, rapid circulation of hot air, accurately adapted and graduated heat, and 

 at all times a considerable portion of humidity. It will be noticed that each of 

 these points stand directly contrary both to the process of desiccation or kiln 

 drying, and to that of ordinar\- air drying. 



In all forms of life, animated and vegetative, water is the circulating medium 

 of life and growth, until these are perfected, and then reverses its fui'iption, and 

 becomes the minister of death and decay. To absorb the water, therefore, is to 

 stop the integrating or disintegrating process, whichever may be going on, with 

 equal certainty. In the Alden process, the rapid circulation of the fresh, heated 

 current, first stimulates the circulation of the sap in the fruit, and keeps up a 

 rapid oxygenation and super-ripening of the mucous ingredients to grape sugar, 

 so long as any free moisture remains. At the end, the free moisture having 



