MICROSCOPY OF THE COMMON ST/IRCHES. 63 



teration of one kind of starch with another cheaper 

 variety. 



Being finely powdered, starch is in a condition admi- 

 rably adapted for microscopic examination, and needs 

 only to be mounted in some medium which will set off its 

 characteristics by proper contrast. If examined dry, the 

 edges of the grains appear so black as to obscure the 

 view, and most solid mounting media have on the other 

 hand so high an index of refraction that except with 

 polarized light the starch becomes too faint. Water with 

 ordinary illumination gives a good picture; and if the 

 hilum is to be particularly studied, a medium of higher 

 density like clove-oil may be useful. Sometimes the 

 detection of starch may be aided by staining it with a 

 dilute solution of iodine, which produces the blue-black 

 color of the iodo-starch reaction. 



5. Potato-starch. — Potato-starch is produced in con- 

 siderable amount both in New England and in certain 

 Western States, and is used mainly in print-works for the 

 sizing of warp yarn before it is woven. Other starches 

 make a more even and permanent paste, as a rule, but 

 for this particular purpose potato-starch seems best 

 adapted. 



As viewed with a hand-lens potato-starch may be at 

 once distinguished from most other varieties by the fact 

 that a mass of it appears to be studded with glittering 

 points, while corn-starch or wheat-starch is of a dull dead 

 white. Under the microscope potato-starch is seen to be 

 made up of large grains, .05-. 12 mm. long, of a flattened 

 ovoid shape, with a smooth and regular outline. As in 



