54 TRANSPIRATION IN A DESERT PERENNIAL. 



temperature determination, i. e., in the turpentine, their specific heat was 

 determined last; meanwhile readings for their initial temperature were taken 

 as follows. 



Turpentine at air-temperature was placed in two calorimeters and the 

 whole allowed to come to equilibrium on a shaded stand near the tree to be 

 used. Leaves were quickly severed from their twigs by means of wooden- 

 tipped forceps and then placed on white glazed paper, from which they were 

 transferred with all possible speed to one of the calorimeter cups, the other 

 being kept for a control. The contents of both calorimeters was kept in 

 constant slow motion by use of the stirrers. Temperatures were read every 

 half minute before and after the introduction of the leaves. 



A determination of the specific heat of the leaves was made by heating 

 turpentine to about 30 C, then placing it, in the same careful way as above, 

 into the turpentine and leaves just used in the temperature readings. Tem- 

 peratures of the contents of both liquids were taken accurately just before 

 and after the mixing. The specific heat of the leaves was calculated from 

 the equation, 



[AiSa) +LOSfe) -hC] [Ta-Tc]=B{Sh) (Tc-Th) (2) 



where 



A = weight of turpentine containing leaves. 



5 = weight of turpentine added to A, and leaves. 

 Sa, Sb = specific heat of turpentine. 



L = weight of leaves. 

 Se = specific heat of leaves. 

 Ta = initial temperature of A and L. 

 Tb = initial temperature of B, 

 Tc = temperature of mixture. 



C = heat equivalent of the calorimeter. 



After the value of Se had been found it was substituted in the equation 



[A{Sa) + C] [Ta-Tc] = LiSe) (Tc-Tb) (3) 



where 



A = weight of turpentine prepared to receive leaves from the plant. 



L = weight of leaves. 

 Ta = initial temperature of turpentine. 

 Tb = initial temperature of leaves, 

 Tc = temperature of mixture. 

 Se and C = same as in previous cases. 



Since Tb is now the only unknown quantity in equation 3, the original 

 temperature of the leaves can be easily calculated. 



