1. Materials

Potato starch, dextrin, dextrose, maltose, lactose, saccharose, and cellulose (represented by absorbent cotton and ashless filter paper).

2. Preparation

(1) To Prepare Fehling's Solution(a) Into a half liter, glass-stoppered bottle put 34.64 grams CuSO4, c.p., and enough H2O dist. to make 500 c.c. Label the solution: Fehling's Solution (a), (b) Into a similar receptacle put 173 grams of potassic-sodic tartrate (Rochelle salt), and 50 grams of NaOH, weighed in sticks; add enough water to make 500 c.c. Label: Fehling's Solution (6). For use, mix these solutions in equal parts. A convenient quantity for the following experiments is 100 c.c. of each solution.

(2) Prepare a starch paste by rubbing 1 gram of starch to a creamy consistence with water, add 50 c.c. of distilled water, and boil.

(3) Prepare a dilute solution of iodin by direct solution in water or by diluting an alcoholic solution.

3. Experiments And Observations

(1) Put a little dry starch into an evaporating dish; add some dilute iodin. The starch turns blue. Pour a few drops of starch paste into a test-tube; add a few drops of iodin. Iodin may be used to detect the presence of raw or of cooked starch.

(2) Put some raw starch into a test-tube or beaker; add water and stir. The starch does not seem to be at all soluble in water. Stir or shake the mixture to bring the starch into suspension in the water; pour upon a filter. A clear filtrate passes readily through. Test the filtrate for starch; result, negative; pour a few drops of iodin upon the filter, starch present.

Conclusions:

(a) Potato starch is insoluble in cold water. (6) The granules of potato starch will not pass through common filter paper.

(3) Dilute a few centimeters of starch paste; pour it upon a filter; to the filtrate add iodin. The blue color indicates that in the cooking of starch the grains are broken up into particles sufficiently small to pass readily through the meshes of common fiber paper.

(4) In order to determine whether dilute starch paste will, in response to the laws of osmosis, pass through an animal membrane, fill a dialyzer with dilute starch paste. Set aside to be tested one or two days later.

(5) Add water to dextrin in a beaker; stir with a rod. Dextrin is readily soluble in cold water. To a small portion add iodin. The solution will probably assume a wine-color; the typical reaction of erythrodextrin. The color fades presently.

(6) Fill a dialyzer with diluted dextrin solution-and leave for subsequent examination. Test the next day to find if dextrin passes through.

(7) Add water to dextrose; it is readily soluble. Add iodin to a portion of the solution; result, negative.

(8) Fehling's Test for a Reducing Sugar - To a few drops of the solution add several cubic centimeters of Fehling's solution and boil. A yellowish precipitate of cuprous oxid (CuO) appears. If the boiling is continued the color changes to a brick-dust red.

(9) To a solution of maltose add Fehling's solution and boil; the copper solution is reduced, and CuO is precipitated.

(10) To a solution of lactose add Fehling's solution and boil; reduction takes place.

(11) Subject a solution of saccharose to the Fehling test. No reduction occurs. Vary the test by boiling the solution with a few drops of dilute HC1 before adding the Fehling solution. The acid splits the disaccharid cane sugar into its monosaccharid components, one of which reduces the Fehling solution.

(12) Trommer's Test for a Reducing Sugar - To any liquid suspected of containing a reducing sugar, add a few drops of dilute CuS04 solution; to this mixture add an excess of NaOH (or KOH); boil; if the suspected liquid contains a reducing sugar the CuS04 will be reduced with precipitation of CuO. Subject all of the solutions of sugar in turn to the Trommer test. Note that the appearance is practically the same as with the Fehling test. Any differences are due only to a difference in the proportions of the two reagents. The Fehling test is the more satisfactory one.

(13) Fill a dialyzer with a dilute solution of dextrose for subsequent examination.

(14) Fill a dialyzer with a dilute solution of maltose or lactose for subsequent examination.

(15) Fill a dialyzer with a dilute solution of saccharose for subsequent examination.

(a) How may carbohydrates be classified? (I. monosaccharids, II. disaccharids, III. polysaccharids.)

(b) Which class has the lowest grade of hydrates?

(c) How many of this class are soluble in cold water?

(d) How many are diffusible?

(e) Which class has the highest grade of hydrates?

(/) Are all of those which belong to classes I. and II. soluble in water?

(g) Which are diffusible?

(h) How many of the carbohydrates reduce CuS04 in the presence of an excess of NaOH or KOH?

(i) How many of the carbohydrates are diffusible?

(j) How may one determine whether or not cane sugar passed through the animal membrane?