242 
WANDERINGS IN CHINA. 
Chap. XV. 
of an infusion of black tea. The same action takes place 
by the exposure of the infusions of many vegetable sub- 
stances to the oxidising influence of the atmosphere ; 
they become darkened on the surface, and this gradually 
spreads through the solution, and on evaporation the 
same oxidised extractive matter will remain insoluble 
in water. Again, I had found that the green teas, when 
wetted and re-dried, with exposure to the air, were 
nearly as dark in colour as the ordinary black teas. 
From these observations, therefore, I was induced to 
believe that the peculiar characters and chemical dif- 
ferences which distinguish black tea from green were to 
be attributed to a species of heating or fermentation, 
accompanied with oxidation by exposure to the air, and 
not to its being submitted to a higher temperature in 
the process of drying, as had been generally concluded. 
My opinion was partly confirmed by ascertaining from 
parties conversant with the Chinese manufacture, that 
the leaves for the black teas were always allowed to 
remain exposed to the air in mass for some time before 
they were roasted." 
Here, then, we have the matter fully and clearly ex- 
plained ; and, in truth, what Mr. Warringi^on observed 
in the laboratory of Apothecaries' Hall may be seen by 
every one who has a tree or bush in his garden. Mark 
the leaves which are blown from trees in early autumn ; 
they are brown, or perhaps of a dullish green, when they 
fall, and yet, if they are examined some time afterwards, 
when they have been exposed to air and moisture in 
their detached state, they will be found quite as black 
as our blackest teas. 
