TEAS METHODS OF ADULTERATION. 881 



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. 1 According to Y. Kozai 2 the 

 maximum amount of facing in the green teas of Japan is about 0.4 per 

 cent. 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 

 gelatiir 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. c//., 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 j 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. 



1 Food, A. H. Hassall, pp. 122 to. 129. 



8 Bulletin No. 7, Imperial College of Agriculture, p. 28. 



3 See method for estimation of tanniu, p. 890, 



