BAIRD &TATLOCK (LONDON) LTD. 



4516 



4516 T Recording Transpirometer, devised by Prof. Blackman and Mr. Paine, Imperial College 

 of Science and Technology. 



Price of Parts as Figured. 



A. Solenoid on Stand . . . . . . . . . . 3 15 o 



B. Balance with Electrodes . . . . . . . . . . 5 lo o 



C. Clockwork Drum on Stand . . . . . . . . . 3 10 o 



D. Aspirator Bottle on Stand . . . . . . . . . . i 10 o 



E. Electro-magnetic Time Marker on Stand . . . . . . 250 



F. Aluminium Outer Pot, 5 in., as Fig. 4509 . . . . . . 066 



Price of complete apparatus without battery 

 DESCRIPTION OF APPARATUS. 



This apparatus is designed to give a continuous record of the transpiration of a potted plant. The apparatus, 

 which is shown in the figure, consists of a balance, a vessel giving a regular flow of water-drops, a tube which is 

 moved to and fro by a pair of solenoids and in its forward position receives the drops of water, a magnetic recording 

 pen moving on a revolving drum, and a battery. 



The flower pot is placed in an aluminium outer vessel rendered water-tight by a sheet of rubber clamped 

 to its rim. Through the rutber project the stem of the plant and also a short open glass tube fixed firmly in 

 the soil below. Through this tube the soil receives automatically, from time to time, additions of water exactly 

 equal in amount to that lost in transpiration. The balance is provided with a " damper " in the form of a metal 

 disc (seen underneath the pan on the left) moving in a fluid of suitable viscosity (such as lubricating oil or glycerine) ; 

 this prevents movements of the balanced pans in response to slight air currents. Attached to the pans of the 

 balance are ebonite cups containing mercury, and above each pan is a pair of platinum points which can be raised 

 or lowered by means of fine milled heads. 



The platinum points are in electrical connection with the pair of solenoids (seen on left) and the recording 

 pen (on the right). Through the solenoids passes a metal tube bearing a small funnel at one end. The tube is 

 so arranged that in its forward position the funnel stands just above the mouth of the glass tube projecting from 

 the soil of the pot. A tube connected with a reservoir normally delivers into the funnel a regular stream of drops 

 of water of uniform size, which are conducted away to the vessel placed at the other end of the tube. The pressure 

 of water is kept constant by an open glass tube passing through the stopper of the reservoir, and the rate of flow 

 can also be regulated by a stopcock. As long as the pans of the balance remain nearly level no water can fall 

 into the pot, but as the plant loses weight by transpiration the left-hand pan rises with its mercury cup and so 

 completes an electrical circuit through the pair of platinum points on that side. A current then flows through 



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