10 Nov., 1917.] Evaporation of Apples. 679 



building best adapted to his particular needs. Hence the detailed 

 discussion which follows is confined to the construction and operation of 

 the actual dr^-iiig units — the tunnels. 



The Tunnels. 

 Tlie number of tunnels to be constructed must be determined 

 in every case by the volume of fruit to be handled. It needs 

 to be emphasized, however, that the length and size of the individual 

 tunnel is not to be modified at the pleasure of the builder. It is usually 

 difficult or impossible to secure satisfactory and economical results with 

 tunnels more than 20 feet in length, since further increase in length 

 retards air movement and therefore slows down the drying. A tunnel 

 higher than 6 feet, or carrying more than 16 or 18 tiers of trays, will 

 dry very slowly on the upper trays, while the work of removing or 

 inserting trays at the top will be incomenient and fatiguing. For the 

 sake of convenience in handling, 3 feet in width and 4 feet iu length 

 should be the limit in size of the trays. Consequently, tunnels 

 20 X 6 X 3 feet are as large as can be efficiently operated, and attempts 

 to increase any of the dimensions are likely to result in constant trouble 

 and lowered efficiency. A tunnel of the dimensions just indicated will 

 carry 18 tiers of five 3x4 trays, or 90 trays, each having a drying 

 surface of 12 square feet. Each tray, when spread to a depth of 

 1^ inches with apples, will hold about 25 lbs. of fresh fruit, giving a 

 total capacity of 2,250 lbs., a quantity which would be yielded by 

 65-70 bushels of apples. Such trays will carry 25 to 30 lbs. of prunes, 

 or 16 to 20 lbs. of raspberries or loganberries. The time required foi 

 drying will depend to such a degree upon the circulation of air though 

 the tunnels that any statements must be taken as only indicative of what 

 may be expected; apples will require- 7 to 16 hours, berries 12 to 17, and 

 prunes 28 to 40 hours at the temperatures recommended in a later para- 

 graph. 



The floor of the tunnel slopes uniformly from end to end, the inclina- 

 tion most generally employed being 1\ or 2 inches per foot length. 

 Two differing types of construction are employed; in one, the tunnel is 

 tightly floored with sheet-iron throughout its length except for a distance 

 of 2 to 4 feet at its lower end, which is directly over the furnace. In 

 the second type, the tunnel has no floor, but is continuous with the 

 furnace room. In either case the furnace stands beneath the lower end, 

 and an arrangement of piping similar to that described as being used 

 in kiln evaporators distributes the heat throughout the length of the 

 tunnel. Each of these arrangements has its strong advocates; that last 

 described obviously makes somewhat better use of the heat produced by 

 the fuel. 



If a number of tunnels are to be constiTJcted, it is advisable to build 

 them in sets of three arranged side by side and heated by the same 

 furnace. In case the tunnels are to be constructed in blocks of three, 

 the furnace room should be made of the same size as the block of three 

 tunnels, except that it is 2 feet longer, or 22 x 10 feet inside the walls. 

 This added 2 feet gives space for the furnace, which is to be set at the 

 lower end of the tunnels (see diagram. Fig. XIX.). The walls of the 

 furnace room may be built of stone, concrete, concrete blocks, or metal 

 lath and plaster. The outer walls of the group of tunnels are merely 



