ch in one fourth of a pint of
water and heat gradually to boiling, stirring well. Then add enough water
to form a thin liquid and fill a test tube half full. Add to this a few
drops of a solution of iodine. (Prepare by dissolving a crystal of iodine
in 25 cubic centimeters (1/20 pint) of a solution of potassium iodide in
water and add water to this until it is a light amber color.) The starch
solution is turned blue, _(b)_ Cut with a razor a thin slice from a
potato. Place this in a weak solution of iodine for a few minutes and then
examine with the microscope, using first a low and then a high power.
Numerous starch grains inclosed in cellulose walls will be seen (Fig. 60).

_Dextrose, or Grape Sugar._--Place a solution of the substance supposed to
contain grape sugar in a test tube and add a few drops of a dilute
solution of copper sulphate. Then add sodium hydroxide solution until the
precipitate which first forms is redissolved and a clear blue liquid
obtained. Heat the upper portion of the liquid slowly to near the boiling
point. A little below the boiling point the blue color disappears and a
yellow-red precipitate is formed. If the upper layer of the liquid is now
boiled, the color deepens and this may be contrasted with the blue color
below. Apply this test to the sugar in raisins and in honey.

_Fat._--Fat is recognized by its effect on paper, making a greasy stain
which does not disappear on heating and which renders the paper
translucent. Try butter, lard, or olive oil. Also show the presence of fat
in peanuts by crushing them in a mortar and rubbing the powder on thin
paper. If the substance to be tested contains but little fat, this may be
dissolved out with ether. If a drop of ether containing the fat is placed
on paper, it evaporates, leaving the fat, which then forms the stain.

*To show the Effect of Alcohol upon Proteid.*--Place some of the white of a
raw egg in a glass vessel and cover it with a small amount of alcohol. As
the albumin (proteid) hardens, or coagulates, observe that the quantity of
clear liquid increases. This is due to the _withdrawal_ of water from the
albumin by the alcohol. Since the tissues are made up chiefly of proteids,
a piece of muscle or of liver may be used in the experiment, instead of
the egg, with similar results.

*To illustrate the Digestive Process.*--To a tumbler two thirds full of
water add a little salt. Stir and observe that the salt is dissolved.
Taste the solut