244 EXPERIMENTS WITH STEAM. 



stance, but none with indigo as represented by 

 the green-tea merchants. 



On what the colour of black tea more particu- 

 larly depends, when manipulated with care, I shall 

 attempt in a subsequent chapter to explain. 



I next tried some experiments to ascertain how 

 far the agency of steam might be rendered subser- 

 vient to the manipulation of tea : but having no 

 other instruments at hand, than the rude vessels 

 already described, I had no means of confining the 

 steam, except with cloths, and thus endeavouring 

 to raise the heat above the boiling point. For the 

 first part of the process, the heat of boiling water 

 so employed was not sufficient to produce the 

 crackling of the leaves described by Koempfer : nor 

 a sufficiently quick evaporation of the fluids, so 

 that it required considerable force to express the 

 remaining juices before the leaves could be perfectly 

 rolled. For the final drying of green tea, it seemed 

 to answer, and might perhaps be used with advan- 

 tage. It is necessary, however, to lower the heat 

 of the water as the leaves dry, for I found by this 

 experiment that the heat produced by boiling water 

 was too great for the final desiccation of green tea. 



With respect to machinery, it is obvious that 

 sifting machines, in lieu of sieves worked by hand, 

 might be employed with advantage in separating 

 the different kinds of leaves of green tea, in addi- 

 tion to the winnowing machine already used for 

 the purpose of separating the young Hyson and 



