I2 CHEMICAL, MEDICAL AND DIETICAL PROPERTIES. 



reason that the substance must have some influence on 

 the digestive organs. 



For the estimation of tannin in tea various processes 

 are in use, a tritration by means of a standard solution 

 of gelatine, which depends upon the well-known property 

 possessed by gelatine of forming insoluble compounds 

 with tannin being the most effective, but tedious and 

 difficult. A much more simple and promising method 

 consists in tritrating by means of a standard solution of 

 lead, the point of saturation being indicated by the red 

 color struck by an ammoniacal solution of ferricyanide 

 of potassium, one drop of this solution being capable of 

 coloring one milligram of tannin dissolved in 100 parts 

 of water, the exact strength of the solution of lead being 

 ascertained with a standard solution of tannin. In using 

 the solution of lead, 10 drops of it are first diluted with 

 9 times its volume in water, and the tea infusion dropped 

 into it from a graduated burette until the indicator strikes 

 a red with the drop of the indicator. The infusion of 

 tea is made by boiling 2 grains of the leaves in water and 

 afterwards diluting it to 250, it being understood that the 

 smaller the quantity of this infusion required to saturate 

 the 10 parts of the lead solution, the higher the percent- 

 age of tannin in the sample of tea treated. This test is 

 specially applicable for ascertaining whether Black tea in 

 particular has been mixed with spent leaves. By taking 

 the normal percentage of tannin in pure Black tea at 10 

 and the percentage of tannin in spent tea as 2, the differ- 

 ence is the extent of adulteration. 



There is a great variability in the amount of tannin 

 contained in the different varieties of tea, varying in 

 quantity according to the country of production, kind, 

 quality, and state of growth when picked. In six sam- 

 ples of China Oolong teas recently tested, the percentage 



