248 



HARDWICKE'S SCIENCE-GOSSIP. 



ADULTERATION OF TEA, AND A NEW 



PROCESS FOR THE EXTRACTION OF 



CAFFEINE OR THEINE, 



By A. B. Griffiths, Medallist in Chemistry 

 AND Botany, &c. 



THE tea-plant [Thca Chincnsis) belongs to the 

 natural order Ternstrrniiacea?. It bears white 

 flowers like the wild rose. The calyx is polysepalous 

 and inferior ; the corolla is polypetalous and hypo- 

 gj'nous ; the stamens or male organs of the plant 

 are indefinite, polyadelphous and hypogynous ; and 

 the pistil or female organ of the plant is syncar- 

 pous and superior. The tea-plant is an evergreen ; 

 the leaves, which are of various sizes, are somewhat 

 similar to those of the rose ; they are serrated and 

 arranged on the stem alternately. 



The tea-plant is indigenous to China, but has 

 been of late years introduced into India and Japan. 



Fig. 146. — Thcaviridis. 



It was first used in this country in the seventeenth 

 century. The chemist has nothing or very little to 

 do with the flower of the plant. It is the leaves to 

 which his attention is drawn, because of their use as 

 an article of diet by a large proportion of the human 

 race. 



Tea is sometimes adulterated with leaves of other 

 plants, as for instance sloe, ash, hawthorn, &c. ; 

 but by a careful microscopical examination these 

 adulterants can be easily found out. Genuine tea- 

 leaves, when moistened with hot water and opened, 

 and then examined by the microscope, show a very 

 characteristic venation ; when once seen, this character 

 will not be easily forgotten. 



The midrib passes from the petiole to the end of 

 the leaf ; and the veins proceeding from the midrib 

 are parallel to each other, but these veins curve a 

 little towards the edge of the leaf. By this character 

 tea may be recognised from other leaves. The edge 

 of the leaf of the tea-plant is serrated, but this is not 

 an essential character. Tea is adulterated in other 

 ways besides the admixture of foreign leaves. Firstly, 

 the leaves are often "faced" or artificially coloured 



with Prussian blue and turmeric, or indigo and talc- 

 powder, to give a green colour. Black tea is often 

 " faced " with plumbago. Secondly, the leaves 

 are sometimes mixed with sand and other mineral 

 substances ; all these bodies can be detected by 

 microscopical and chemical analysis in the ordinary 

 way. There ' is still another method in which this 

 leaf is rendered not genuine ; that is, by the practice 

 of selling the tea more or less exhausted. 



The principal ingredients in the ash of tea-leaves 

 are potash, protoxide of manganese, and phosphoric 

 acid. The following table will show the percentage 

 of these ingredients of the ash from a sample of 

 genuine tea, and the same sample when completely 

 "spent":— 



Genuine "Souchong." 



Potash 38"456 



Phosphoric Acid . . i4'62i 

 Manganese Protoxide I'lot, 



Spent " Souchong." 



Potash 7 '5^3 



Phosphoric Acid . . 24*900 

 Manganese Protoxide 1*809 



A pretty fair judgment as to adulteration of a 

 sample of tea can be arrived at by a simple process 

 of my own. This process is based on the ex- 

 traction of the theine contained in tea ; and ascer- 

 taining the percentage of theine extracted from a 

 known weight of tea. Tea contains from a half to 

 five per cent, of theine. 



The way to proceed in this new process of extrac- 

 tion is to weigh out about iSo grammes of the sample 

 of tea, and boil with 2 litres of distilled water in a 

 glass beaker ; allow the infusion to boil for five 

 minutes ; then add to the infusion a small quantity 

 of glass (reduced to a fine powder) and magnesic 

 oxide. Keep this mixture in strong ebullition for 

 about twenty or twenty-five minutes ; at the same 

 time occasionally stirring with a glass rod. Again, 

 add 250 c.c. of water, and boil for fifteen minutes 

 longer. The aqueous extract is now to be evaporated 

 very carefully to complete dryness. The residue left 

 on evaporation is to be treated three or four times 

 with rectified ethylic ether by means of Payen's 

 percolator. 



Three or four treatments with ether generally 

 suffice to remove all the theine. The last portions 

 of the ethereal washings when evaporated should 

 leave no residue. These ethereal solutions are to be 

 gently heated, and then allowed to evaporate in a 

 shallow dish of known weight. The solid remaining 

 is the pure alkaloid theine. 



The dish and its contents are now weighed. 

 The weight of the dish and the theine, minus the 

 weight of the dish alone, gives of course the weight 

 of the theine. From this, the percentage of theine in 

 the original weight of tea can be ascertained by means 

 of simple proportion. 



If the percentage is less than a half per cent., you 



