. 
882 FOODS AND FOOD ADULTERANTS. 
SPENT OR EXHAUSTED LEAVES. 
The detection of spent or partially exhausted leaves in teas is not a 
simple problem. The chemical methods all depend upon the proportion 
of certain of the soluble constituents which remains in the tea leaves. 
A large number of analyses of genuine teas made by different chemists 
Show a very wide range in the percentage composition of teas; hence 
the difficulty in obtaining a basis for comparison. A genuine tea may 
contain as little as 10 per cent tannin or even less, and as high as 25 
per cent. It is evident from this that the percentage of tannin can not 
be depended upon for the detection of the admixture of spent leaves. 
A large quantity of such exhausted leaves would be required to reduce 
a tea containing a high percentage of tannin to the average percentage. 
The same may. be said, in a measure, of each of the soluble constituents 
of the leaves. Hence, we see the difficulty in securing data of value on 
this point from a determination of the soluble matters. The only 
estimation of this kind that is of value, and its value it must be said is 
but relative, is the percentage of extract matter. A large number of 
analyses by different authorities shows a range in the extract matter 
of from 26 to 50 per cent of the air-dried tea. This extract is not the 
total soluble matter of the prepared leaf, but is the soluble matter 
extracted under certain conditions which are fully described on page 892. 
One of the most valuable series of analyses of genuine teas that have 
been made is that of Mr. Joseph F. Geisler.!. This chemist obtained 
the following averages of extract matter: 
| | | Extract— 
Peaeene| “bolting. econ 
| * in 100 parts) y 
| water. 
Indian tea: | Per cent. | Per cent. | Per cent. 
Wisp ain e Rania aie ao Sao ee un andere 6.19 | 39.66; 45.64 | 
Ai Ghithine: -Pesee ad aweconaceeata Hseace 5.36 | 37. 80 41. 32 | 
INCL ACe oe Sen oe Sees de ie 5.81 | 38.77 42. 94 
Average for tea dried at 100° C...|.......... | 41.13 45. 58 | 
Oolong tea: ‘ | | 
Maxima stem ree ann rete 6. 88 44.02 | 48.87 
IMUnineee See nk a Se his | «BL 09 34.10} 40.60 
Aivenape SUee tBe ee i bees wees (Preece 37.88 | 43.32 
Average for tea dried at 100° C...|.--....-.. 40. 22 | 46. 03 
Congou tea: : E 
MERON SRS a See Sa OGSEo aoe ORI 32. 14 | 37. 06 | 
Mia ee he eee ee ae ere 7.65 23. 48 | 27. 48 
IANOLAGE) ae hse ses eae te nie Ae | 8. 37 28.40 | 34,35 
Average for tea dried at 100° C.-.-|.....-.--. 30.98 37. 48 
Formule have been given, notably by Allen, for the calculation of 
the proportion of spent leaves from the amount of extract matter. Little 
1 Joseph F. Geisler in Am. Grocer, October 23, 1884; also in Prescott’s Organi¢ 
Analysis, pp. 505 to 512, 
N 
