MICROSCOPY OF THE COMMON STARCHES. 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, .os—.12 mm. long, of a flattened 
ovoid shape, with a smooth and regular outline. As in 
