262 DIFFICULTY IN TESTING 



both classes of tea, black and green, although the 

 green tea leaves require generally a somewhat 

 higher temperature, in consequence of their greater 

 humidity or aqueous condition, and because they 

 are roasted as soon as gathered, without any 

 previous evaporation of the fluids. 



In the subsequent and final stages of the mani- 

 pulation, or the process of drying, an essential differ- 

 ence arises in the mode of manipulation, as well as in 

 the application of heat. On this depends, as already 

 demonstrated, the distinctive colour of green tea 

 more than on any management of the heat, or any 

 difference of temperature. The black is dried in 

 sieves through the interposition of one of the 

 slowest conducting powers of heat, — air; and 

 the green tea by contact with heated iron, one of 

 the quickest conducting powers. Moreover, the 

 leaves of the black tea are kept in a quiescent 

 state, receiving the full impression, though slowly, 

 of the heat thus transmitted; while those of the 

 green tea are kept in constant motion, besides 

 being fanned ; so that this latter tea is exposed 

 during the process of manipulation to the alternate 

 impressions of heat and cold in rapid succession, 

 by the free admission of air to every part of the 

 leaves. Thus a rapid evaporation of the fluids 

 is produced, and consequently rapid desiccation. 

 But how this effect, or the amount of heat thus 

 impressed on the leaves in these alternations of a 

 heating and cooling process is to be measured, 

 seems to me a matter of no small difficulty. All 



