for gronsoing Plants in Rooms, 



119 



18 



^ 



Jigs> 1 7} 18. is 3 ft. 7J in. by 29,^ in. A piece of tinned brass tube, 

 a quarter of an inch in diameter, and a foot long, is passed through 

 the bottom of the soil trough at one corner, and soldered to the 

 lead lining. The part of the tube within the trough rises per- 

 pendicularly, and ends a little above the level of the surface of 

 the soil. The shorter portion, which is without the bottom of 

 the trough, is turned horizontally, and terminates in a brass con- 

 necting screw, to which a corresponding screw of a small stop- 

 cock is attached ; to this stopcock a second stopcock, previously 

 inserted in the end or corner of a M'Intosh air-pillow, is to be 

 screwed on. This air-bag should be of such dimensions that it 

 may be concealed within the frame on which the soil trough 

 stands, in the hollow of which it may be supported by tapes or 

 strings passed from side to side under the bag. At the time 

 the bag is attached to the stopcock on the brass tube, the 

 temperature of the air in the conservatory should be observed, 

 and if it be at or near its maximum of elevation (and the air con- 

 sequently near its maximum of dilatation), the bag should be 

 nearly full of air; and vice versa, if the temperature be low, the 

 bag should be very flaccid when attached, in order that it may 

 have capacity to receive the air expelled from the case when di- 

 latation takes place on the temperature being raised. By this 

 means the air contained within the case and bag, though con- 

 stantly changing place, will never communicate with the external 

 air, and its identity will be maintained with considerable exactness. 



