204 Comparative Analysis 



smallest portion of essential oil, or other vegetable matter could 

 be detected in it*. 



The above experiments shew that the quantity of astringent 

 matter precipitable by gelatine is somewhat greater in green 

 than in black tea, though the excess is by no means so great as 

 the comparative flavours of the two would lead one to expect. 

 It also appears that the entire quantity of soluble matter is 

 greater in green than in black tea, and that the proportion of 

 extractive matter not precipitable by gelatine is greatest in the 

 latter. 



Sulphuric, muriatic, and acetic acids, but especially the first, 

 occasion precipitates in infusions both of black and green tea, 

 which have the properties of combinations of those acids with 

 tan. Both the infusions also yield, as might be expected, 

 abundant black precipitates with solutions of iron ; and when 

 mixed with acetate, or more especially with sub-acetate of lead, 

 a bulky bufF-coloured matter is separated, leaving the remain- 

 ing fluid entirely tasteless and colourless. This precipitate was 

 diffused through water, and decomposed by sulphuretted hy- 

 drogen ; it afforded a solution of tan and extract, but not any 

 trace of any peculiar principle to which certain medical effects 

 of tea, especially of green tea, could be attributed. 



One property of strong infusions of tea, belonging equally to 

 black and green, seemed to announce in them the presence of a 



• «' I distilled half-a-pound of the best aud most fragrant green tea, 

 with simple water, and drew off an ounce of very odoroiis and pellucid 

 water, free from oil, and which, on trial, shewed no signs of astringency." 

 Lettsom's Natural History of the Tea Tree, London, 1799, 4to. 



Some of Dr. Lettsom's experiments would seem to shew that thenoxious 

 efifects of tea are referable to the volatile and odorous principle which 

 thus passes off in distillation ; and he thinks that those who sufifer from 

 them, but yet cannot omit this favourite beverage, might take it with more 

 safety if previously boiled for a few minutes to dissipate the fragrant prin- 

 ciple. In all the forms which Du Halde relates for administering tea as a 

 stomachic medicine among the Chinese, it is either ordered to be boiled 

 or otherwise so prepared as to dissipate its fragrancy. 



