92 



The Supplement to the Tropical Agriculturist 



to tbe electorate. How will they vote ? Will they 

 insist upon having tea, and what else they 

 need, Sreo'of' the limes ? If that should happen, 

 will there beqnoa'^h for all who want to buy it ? 



We are brought hack to discuss how much can 

 be produced and obtained. Estimates being 

 worthless, the probabilities are all that can be 

 shown ; they are that more tea will be gathered 

 from the existing acreage, weather and labour 

 permitting, in the three countries upon which 

 we depend for our supplies. Whatever orders 

 may be given, there will be strong inducement 

 to gather weighty crops, so long as buyers go on 

 bidding almost as much for common tea as they 

 pay for good qualify. And they will be welcome 

 — no longer something to deprecate, and speak 

 about with fear and trembling, but to be 

 deemed a boon, for unless we get them our 

 trade cannot expand, nor will the poor, who 

 want tea cheap and good, obtain it. 



Large crops, moreover, will be usetul to 

 owners of estates if they happen to find their 

 labour bills are heavier ; rice dear perchance ; 

 manuring somewhat costly ; or London charges 

 rising. A failure to secure them, or any serious 

 setback to China's industry, would lead to inte- 

 resting developments, and give the writer of 

 next year's review something to tell worth hear- 

 ing.— Daily Telegraph, Dec. 26. 



THE CHEMISTRY, PHYSIOLOGY AND 

 AESTHETICS OF A CUP OF TEA. 



Caffeine Tank at k as the Chief Constituent 

 of Tea Infusion. 

 The view that caffeine exists in an infusion of 

 tea in the form of a definite compound with 

 tannin is sustained by further experiments. In 

 a previous article upon the subject it was shown 

 that when an infusion of tea (which always 

 exhibits an alkaline reaction) was acidified with 

 any acid a flaky buff-coloured precipitate settled 

 out, especially in the cold, which proved to con- 

 tain chiefly caffeine.tannate. Further, the propor- 

 tion of caffeine to tannin in this precipitate was 

 found to be one of the former to three of the 

 latter,and the suggestion was the compound con- 

 sisted of one molecule of caffeine Cs Hio N4 O2 

 with a molecular weight of 194, associated with 

 one molecule of quercitannic acid C28 H23 O15 

 with a molecular weight of 602. In the pre- 

 vious article the formula was strongly given as 

 C20 H20 O 9. The ratio of caffeine to tannin in 

 such a compound would be 1.: 31. The follow- 

 ing is an example of the analysis of this precipi- 

 tate from a good India Tea : — 



Caffeine ... ... 20'93 per cent 



Tannin ... ... 62'80 ,, 



Resinous and oily matters 



(by difference) ... 16-27 „ 



Total ... ...100-00 „ 



The precipitate amounted to 9'84 per cent of the 

 tea used in the infusion. A further experiment 

 gave the following results : — 



Caffeine ... ... 20'89 percent 



Tannin ... ... 62 66 „ 



Resinous and oily matters 



(by difference) ... 16*45 ,, 



It follows that the precipitate obtained on 

 making an infusion of tea acid consists princi- 

 pally of caffeine and tannin in the ratio approxi- 

 mately of 1 of the former to 3 of the latter. The 

 presumption is that caffeine tannate is the chief 

 body thrown out of solution by the addition of 

 acid. 



When, however, this precipitate is removed by 

 filtration and the filtrate is saturated with 

 ammonium sulphate a further separation of 

 buff-coloured flakes takes place. On analysis 

 these flakes show the following composition : — 

 Caffeine ... ... 24'13 per cent 



Tannin ... ... 75 - 80 „ „ 



Tannin —3-14 



Caffeine 



The ammonium suiphate precipitate amounted 

 to 4 per cent of the tea used in the infusion 

 (5 grammes in 400 cubic centimetres of just 

 boiling water allowed to stand five minutes 

 before pouring off). Calculation shows that 

 this particular tea yielded a total of caffeine 

 tannate of 12"26 per cent. Of this total 8-26 was 

 thrown out by mere addition of acid and 4 00 per 

 cent by subsequent saturation of the filtered 

 acid infusion with ammonium sulphate. The 

 whole can be thrown down at once by adding 

 ammonium sulphate after acidifying the tea 

 infusion with dilute sulphuric acid, When this 

 precipitate is air-dried and sunk in a mixture 

 of 1 of alcohol and 2 of benzene the caffeine 

 tannate is separated from the excess of ammo- 

 nium sulphate crystals and resins and obtained 

 in a comparatively pure state. The solution of 

 caffeine tannate in benzene-alcohol mixture 

 readily yields its tannin to lead oxide (litharge), 

 the caffeine being set free. To give an ex- 

 ample, a certain tea (Indian) yields a total 

 precipitate by ammonium sulphate amount- 

 nig to 1T60 per cent, when dissolved in 

 benzene-alcohol mixture and evaporated to 

 dryness and weighed. The following was the 

 process. A definite volume of the alochol- 

 benzeue solution of the caffeine tannate was evap- 

 orated over a weighed quantity of lead oxide. 

 The dry residue was then made into a thick 

 paste with water and extracted with chloroform, 

 which was poured off and evaporated in a plati- 

 num basin. The residue from the chloroform 

 represents the caffeine contained in the caffeine 

 tannate. The wet lead oxide paste was then 

 dried to constant weight and Che increase of 

 weight shown over the original amount of lead 

 oxide weighed out was regarded to be due to 

 tannin. In this way a residue of 11 60 per cent 

 obtained by evaporating the alcohol-benzene 

 mixture to dryness gave on treatment in the way 

 just described : — 



Caffeine ... ,„ 2 - 80 per cent 



Tannin ... ... 8 -80 ,, 



Total (caffeine tannats) 1160 ,, 

 With another tea the total caffeine tannate 

 extracted from the ammonium sulphate preoipi- 

 tate by benzene-alcohol mixture was 12 - 80 per 

 cent, and the constituents found by lead oxide 

 separation were : — 



Oaffeine ... ... 3'20 per cent 



Tannin ... ... 9*60 „ * 



Total «. ...100-00 



Total (caffeine tannate) 12-80 



