ARTIFICIAL DRYING OF WHEAT. 163 



The remarkable aggregation of heating power thus attained 

 in a small space will be best understood when it is stated 

 that, in a heat-box measuring 27 inches long, 18 inches 

 wide and 16 inches high, 80 effective feet of heating sur- 

 face are collected. 



We have already explained the furnace system by 

 which Mr. Davison warms large volumes of air; that 

 gentleman has recently introduced an exceedingly compact 

 form of heating apparatus to be used in conjunction with 

 a fan. This may be described briefly as a fanner surrounded 

 by a series of convolutions ; these are double, and are filled 

 with steam. The fanner draws air in at the centre, and 

 drives it outwards towards the periphery, and as it winds 

 round and round the convolutions it gets rapidly heated. 

 Each convolution being made up of a double plate, two 

 surfaces are obtained, the inside and outside (see fig. 22). 

 A brief glance at the hot water heating apparatus will suf- 

 fice for our purpose. When heat is applied to a vessel of 

 water, as the particles of water at the bottom get heated 

 they rise up towards the top, while other and colder parti- 

 cles descend to take their place, and getting in their turn 

 heated, rise to give place to colder particles. This con- 

 stant circulation is maintained till the mass is of a uniform 

 temperature; but if the vessel, which we shall suppose a 

 tube, is elongated, and a great portion of its length exposed 

 to the atmosphere, which will rob it of its heat, this uni- 

 formity of temperature will seldom be attained, so that a 

 continual circulation of the particles of water will take place 

 in the tube so long as heat is applied to its lower extre- 

 mity. This is what happens in the hot water apparatus. 

 This arrangement is called the low-pressure apparatus, in 

 which the temperature cannot possibly get above the boil- 

 ing point practically, it is far below this. 



26. As closely connected with the subject of drying 

 grain described, and as indicative of the mode of carrying 

 it out, we translate the following from a Continental journal : 

 The Attention to be given to Gram in Granaries. "The 

 frequent rains which have taken place during the month of 



