ADULTERATION AND DETECTION. 147 



Catechu (soluble salts of iron) is best ascertained by 

 making an ordinary infusion of the leaves, allowing the 

 liquor to cool and pouring it into a cup or glass. Next 

 add a preparation of neutral plumbic acid and separate 

 the precipitate formed by the introduction of the chemical 

 by filtration, and adding a little argentic nitrate to the fil- 

 trate. If catechu be present the residue will turn a dark- 

 brown, the liquid meanwhile acquiring a deep yellow hue, 

 while under the same conditions the liquor of pure tea will 

 remain unaffected. But if the cosmetic be extensively 

 employed, a weak solution of ferric-chloride will cause 

 the precipitate to turn light-green or it may be detected 

 under the microscope if heavily coated. 



Spent and spurious leaves may also be readily detected 

 by the "ash test," through the following deductions : Pure 

 teas, as shown above, contain from 5 to 6 per cent, of ash 

 on incineration, 2 per cent of this being soluble in boil- 

 ing water ; any increase of these parts is a certain indica- 

 tion of the presence of foreign or exhausted leaves in 

 the sample treated. The percentage of ash contained in 

 spent leaves, ranging from loto 30, and in spurious leaves 

 from 40 to 50, in many instances, while the residue of teas 

 adulterated with mineral matter have been known to reach 

 as high as 75 to 80 per cent, of the incinerated sample. 

 The presence of logwood is best exposed by the addi- 

 tion of a few drops of sulphuric acid to an infusion 

 made with the leaves in the ordinary way. If any of 

 the dye be present this acid will cause the liquid to turn 

 a deep red, but if the tea be uncolored the liquor will 

 remain entirely unaffected. Graphite being visible to the 

 naked eye is easily distinguished by its characteristic 

 glossy nature, or can be separated by treating the leaves 

 with boiling water in the usual manner and evaporating 

 the infusion. The substance, if present, will form a 



