. 
TEAS—-METHODS OF ADULTERATION. S81 
The remarks on Prussian blue apply to other facing materials, espe- 
cially in regard to the large quantity of tea that must be consumed in 
order to take even the smallest medicinal dose of the coloring matter. 
The amount of coloring and inert matter (the latter often soapstone) 
usually amounts to a very small percentage of the weight of the tea, 
though statements have been made that the facing sometimes amounts 
to as much as from 1 to 3 per cent.! According to Y. Kozai? the 
Maximum amouut of facing in the green teas of Japan is about 0.4 per 
eent. Excessive facing is evidently a fraud, as it increases the weight 
and price of tea without giving the purchaser a fair return for his money. 
DETECTION OF FACING. 
Facing is usually easily detected by the microscope. A portion of the 
leaf is mounted as an opaque object, the coloring matter appearing in 
small dots. 
Prussian blue—This substance is easily detected by means of the 
microscope. Shake the leaves in a glass cylinder with water and exam- 
ine the detached particles with the microscope. If the coloring matter 
sought is present, transparent particles of a brilliant blue may be seen. 
Prussian blue may often be identified by the microscope on the leaf 
mounted as an opaque object. The particles detached as above may be 
examined chemically as follows: Treat with hot sodium hydroxide solu- 
tion, acidulate with acetic acid, and add ferric chloride. If Prussian 
blue was present in the facing the characteristic blue precipitate will be 
formed. The powdered tea leaf may be examined by the chemical 
method, but it is advisable to remove the tannin by precipitation with 
gelatin’ solution and filtration through powdered kaolin, after acidulat- 
ing with acetic acid. The color of Prussian blue is discharged by 
sodium or potassium hydroxide. 
Indigo.—Under the microscope indigo appears of a greenish blue. 
Its color is not discharged by sodium hydroxide, a distinction from 
Prussian blue. Indigo forms a deep blue solution with sulphuric acid. 
Turmeric.—Turmeric is identified by means of the microscope. 
According to Hassell (op. cit., 143) turmeric consists of characteristic 
yellow cells of a rounded form which are filled with peculiar shaped 
starch granules. On the addition of an alkali the cells turn brown, 
swell up, and the outlines of the starch granules become visible. 
Plumbago.—The microscope is employed in the detection of plumbago. 
A thin slice of the tea leaf will exhibit numerous bright particles if 
plumbago facing has been used. | 
Gypsum, soapstone, etc.—These substances, employed with the color- 
ing matter in facing teas, may be separated by shaking the leaves in a 
cylinder with water. The sediment is examined by the usual qualita- 
tive methods for these substances. 
? Bulletin No. 7, Imperial College of Agriculture, p. 28. 
> See method for estimation of tannin, p. 890. 
