146 THE BANANA 



ago as 1898. It was introduced by Mr. O. Zurcher, the 

 manager at Montpelier for the proprietor, Hon. Evelyn 

 Ellis. It was of the revolving drum type, and was said 

 to turn out five tons of dried banana flour every week for 

 some time. An improved model is now recommended, 

 and may be taken as a type of what is required under this 

 system. It consists of a rectangular cast-iron vacuum 

 chamber with surface condenser and steam-driven vacuum 

 pump. 



The vacuum-drying chamber is designed to remove the 

 water rapidly and at a low temperature. The chamber is 

 iron, closed hermetically by a door. It contains a number 

 of closed heating shelves, arranged one above the other, in 

 which small pipes are fitted for the admission and exit of 

 the heating steam. The shelves are as a rule made strong 

 enough for a test pressure of 90 Ibs. On these are placed 

 trays containing the material to be dried. After the door 

 of the drier, which is fitted with an india-rubber joint, has 

 been closed, a high vacuum of at least 28 in. of mercury 

 or more is created by means of the air-pump, while exhaust 

 steam passes through the heating shelves. At a very 

 moderate temperature of the material that is to be dried 

 about 95 F. (35 C.) the water, owing to the vacuum, 

 begins to evaporate briskly out of the substances, which 

 therefore dry rapidly. The charging of the chamber is 

 simple and easy, and the working clean and reliable. The 

 temperature can be regulated by valves in the steam pipes. 

 The drying, of course, is independent of climatic conditions. 

 By using hot water for heating with an air-pump giving 

 a high vacuum, the evaporation of the water contained in 

 the materials that are to be dried takes place at as low a 

 temperature as 63 F. (17 C.). 



The driers work with a very small consumption of 

 steam. As a rule, only 13 to 15 Ibs. of heating steam are 

 required to evaporate 10 Ibs. of water out of the previously 

 heated substance that is to be dried. This includes the 

 motive power for the air-pump, where the exhaust steam 

 from the air-pump engine is used for heating purposes. 



