124 EXPLOITATION OF PLANTS 
a cheap Ceylon tea contained 5°46 per cent. of tannin, 
while an expensive Ceylon tea gave 7°56 per cent. 
Now, the probable explanation of such figures appears 
to be forthcoming as a result of investigations carried © 
out in rg1z in the laboratories of the Lancet (2). 
Ordinary infusion of tea is a slightly alkaline liquid ; 
if just acidified, it becomes lighter in colour, and as it 
cools a flocculent precipitate is formed, which can be 
brought down more completely by appropriate means. 
It is not unreasonable to suppose that these happenings 
take place when the beverage reaches the acid contents 
of the stomach. An analysis of the precipitate gave the 
following results— . 
CAFFEINE AND TANNIN IN TEA INFUSIONS 
(5 gr. of tea infused for 5 minutes in 4oo c.c. boiling water) 
er Mh Approx. ratio 
3 Amount of Caffeine in Tannin in . 
Variety of Tea. precipitate. precipitate. | precipitate. oe catene to 
China... 68 % 72% 5°08 % 123 
Ceylon. . . IO-I2 2°53 759 | T3 
Indian (Assam) 12°88 3°22 9°66 L3 
The table gives the total amount of the precipitate 
(estimated on the dry tea); and suggests that, as a 
rule, China teas yield it in least amount, and Assam teas 
in greatest. Further, the precipitate is composed of 
caffeine and tannin in the proportions of 1:3. These 
facts led to the view that the precipitate is a definite 
compound which may be described as caffeine tannate, 
so that we arrive at the inspiring conclusion that 
a cup of tea is, broadly speaking, a slightly alkaline 
