THE MICROSCOPE AS DETECTIVE 



purities, the chief being chicory, various starches, 

 ground acorns and date stones. Chicory is really 

 an impurity, though it is one often asked for by 

 coffee-drinkers. It is easy to detect the amount of 

 chicory present in a sample of ground coffee, by 

 throwing a little of the mixture on to water. The 

 chicory sinks at once, whereas the coffee floats 

 for a while because it is oily. In pure coffee there 

 should be no starch and the iodine test will readily 

 show whether we are dealing with a sample free 

 from starch or not. 



Mustard is very rarely purposely mixed with any 

 impurities, in fact it is probably the least likely to 

 be adulterated of any article of food. Under the 

 microscope a large number of small objects, very 

 similar to starch grains, can be seen. They are 

 the cells containing mustard oil and they are not 

 stained blue by iodine. A specimen of pure 

 mustard contains no starch. Pepper is by no means 

 easy to test for impurities. It contains minute 

 starch grains, which can be recognised under the 

 microscope after staining. It is mentioned here 

 because of a very interesting and easily performed 

 experiment that will appeal to every microscopist. 

 Place a little pepper on a clean slide and moisten 

 it with a drop of alcohol, allow it to stand for a 

 minute or so then add a little dilute glycerine, cover 

 the specimen with a cover glass and examine it 

 under the microscope after the lapse of about five 

 minutes. The sight of wonderful prismatic crystals 

 forming one by one in rapid succession will be ample 



145 K 



