142 



Cultivation of the Hof Crop. 



[May, 



The positions most likely to be faulty in this respect are the 

 doors of the kiln and the roof. 



One further point in this connection is worthy of notice ; in 

 some few kilns one finds the position of the fireplaces excavated, 

 so that the firebars themselves are situated at or close to the 

 ground-floor level and the topmost inlet of air above the fires 

 is correspondingly lowered; this arrangement provides for addi- 

 tional effective height and so better draught is obtained 

 economically, provided that facilities are made for easy carriage 

 of coal to and cinders away from the fires. 



In some kilns draught is much curtailed by the narrow 

 apertures through which the air has either to enter or escape 

 from the kilns, especially in still weather when there are no 

 air currents. This restriction of openings is also liable to pre- 

 judice draught when fans are substituted for natural draught 

 in a transformed oast. 



Lastly, it is much easier to establish a good draught when 

 the wind is blowing past the cowl, a contrivance specially 

 fashioned to facilitate suction of air out of the kiln ; in order to 

 increase this aid to draught the kiln should be built in an open 

 situation and trees should not be planted closely around which 

 would tend to shelter the cowl from wind. 



Evaporation. — The drying of the hop is somewhat but not 

 completely analogous to the evaporation of water from a wet 

 cloth, for in the case of the hop the water is contained within 

 the tissues of the cones, partly in the bracts and bracteoles (or 

 " petals " as the hop-grower calls them) and partly in the 

 strig of the hop ; from the former evaporation is rapid, but from 

 the strig, protected as it is by the bracts, evaporation is much 

 slower. 



Water evaporated from the hops passes into the air, which is 

 capable of absorbing varying quantities of water vapour accord- 

 ing to its temperature. For each temperature of the air there 

 is a maximum w^ater vapour content, and if more w^ater 

 vapour is put into such saturated air, then either a mist 

 is formed or water vapour is deposited as dew. Such 

 a deposit of w^ater vapour may occur in hop drying upon 

 the top surface of the hops during the early part of 

 the drying. At 50° F., a frequent temperature of the 

 outside air during drying, air can only contain f oz. of 

 water vapour in 10 cub. yd.: at 100° F.. the temperature at 

 which hop-drying generally starts, air can contain 3J oz. of 

 moisture in 10 cub. yd.: whilst at 150° F.. the temperature at 



