THE MICROSCOPE AS DETECTIVE 



this trouble arises because tea contains a poison 

 called "theine"; it is an alkaloid, one of a large 

 class of chemical substances which are nearly all 

 deadly poisons — cocaine and nicotine are alkaloids. 

 Although theine is poisonous, tea which contained 

 none of this substance would be tasteless and the 

 absence of this substance shows that the tea leaves 

 have been badly prepared. Tea after being gathered 

 should be dried at once, sometimes it is re-dried 

 and this process drives off the theine. For our test 

 we require, in addition to our microscope, two 

 watch glasses, a piece of copper wire gauze and a 

 gas burner or a spirit lamp. Place a little tea in 

 one of the watch glasses and cover with the other 

 watch glass; then heat gently on the wire gauze. 

 In a few minutes drops of moisture will appear on 

 the upper watch glass; after about ten minutes' 

 heating beautiful, long, needle-shaped crystals will 

 begin to appear, with a little further heating we shall 

 obtain a good crop of lovely crystals on the upper 

 watch glass and they make a splendid object for 

 examination under a low magnification. The crystals 

 are of theine, the poisonous component of tea, and 

 the test is used to discover whether the tea has been 

 redried during its preparation; redried tea gives no 

 crystals. 



The examination of cocoa for impurities is a 

 matter rather for the chemist than for the micro- 

 scopist. It contains a vast number of starch grains, 

 not unlike those of rice, except that they are 

 rounded. Coffee often contains a number of im- 



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