569 



The question presents itself, then, — From whence do these distin- 

 guishing peculiarities arise, and to what are they to be attributed ? 

 From observations made in other directions, in the course of the rou- 

 tine work of the establishment to which I am attached, I had formed 

 in my own mind certain conclusions on this subject. I allude to the 

 exsiccation of medicinal herbs ; these are for the most part nitroge- 

 nous plants, as the Atropa Belladonna, the Hyoscyamus niger, the 

 Conium maculatum, and others. The plants are brought to us by the 

 growers or collectors from the country, tied up in bundles ; and when 

 they arrive fresh and cool they dry of a good bright green colour ; 

 but, on the contrary, it is found that if they are delayed in their tran- 

 sit, or remain in a confined state for too long a period, they become 

 heated, from a species of spontaneous fermentation, and when loosened 

 and spread open emit vapours, and are sensibly warm to the hand ; 

 when such plants are dried, the whole of the green colour is found to 

 have been destroyed, and a red-hrown and sometimes a blackish- 

 brown result is obtained. I had also noticed that a clear infusion of 

 such leaves evaporated carefully to dryness was not all re-dissolved by 

 water, but left a quantity of brown, oxidised, extractive matter, to 

 which the denomination Apothem has been applied by some chemists ; 

 a similar result is obtained by the evaporation of an infusion of black 

 tea. The same action takes place by the exposure of the infusions of 

 many vegetable substances to the oxidising influence of the atmo- 

 sphere ; 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 pecu- 

 liar characters and chemical differences which distinguish black tea 

 from green, were to be attributed to a species of healing or fermenta- 

 tion, 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 ex- 

 posed to the air in mass, for some time before they were roasted. Mr. 

 Ball, in his valuable work on the manufacture of tea,* has described 

 in detail the whole routine of these interesting processes, fully 



* ' An Account of the Cultivation and Manufacture of Tea in China,' by Saml. 

 Ball, Esq. 



VOL. IV. 4 D 



