XXVn] TEA 337 



Facing. 



17 general.— tentative. 



Mineral pigments may be detected in the ash, or the tea may be shaken up with 

 a large volume of water, and the water separated from the leaves by a sieve, when 

 the insoluble mineral substances used in facing will settle and can be removed by 

 filtration for further examination, as directed under XI, 1 , the catechu and other 

 soluble substances being in the filtrate. 



18 PARAFFIN AND WAXY SUBSTANCES.— TENTATIVE. 



Spread a quantity of the tea between 2 sheets of unglazed, white paper and place 

 thereon a hot iron. Any greasy substance will stain the paper*. 



PIGMENTS USED FOR COLORING OR FACING. 



19 Read Method^.— Tentative. 



Place 60 grams of the tea in a 60 mesh, 5-6 inch sieve, provided with a top. Sift 

 a small quantity (approximately 0.1 gram) of the dust upon a piece of semi-glazed, 

 white paper about 8 by 10 inches. To obtain the requisite amount of dust, it is 

 sometimes necessary to rub the leaf gently against the bottom of the sieve, but this 

 must not be done until the sieve has been well shaken over the paper. Place the 

 paper on a plain, firm surface, preferably glass or marble, and crush the dust by 

 pressing firmly upon it a flat steel spatula about 5 inches long. Repeat the crush- 

 ing process until the tea dust is ground almost to a powder when particles of color- 

 ing matter, if present, become visible as streaks on the paper. Brush off the 

 loose dust and examine the paper by means of a simple lens magnifying 7h diame- 

 ters. In distinguishing these particles and streaks bright light is essential. In 

 many cases the character of the pigment is indicated by the behavior of these 

 streaks when treated with reagents and examined under a microscope. The 

 crushed particles of natural leaf in either black or green tea appear in such 

 quantity that there is no chance of mistaking them for coloring or facing material. 

 This test should be repeated using black, semi-glazed paper for facings such as talc, 

 gypsum, barium sulphate or clay. 



BIBLIOGRAPHY. 



1 U. S. Bur. Chem. Bull. 13 (VII); Villiers and Colin. Trait6 des Alterations et 

 Falsifications des Substances Alimentaires. 2nd ed., 190&-11. 



2 U. S. Bur. Chem. Bull. 105, p. 48. 

 ' Ibid., 13 (VII), p. 890. 



*U. S. Treas. Dept., T. D. 35244. March 23, 1915. 



* Ibid.; Proc. Eighth Intern. Cong. Appl. Chem., 1912, 18: 301. 



