Weed, Chemistry in the Home.

Wellman, Food Study.

Sherman, Food Products.

Snell, Elementary Household Chemistry.

Leach, Food Inspection and Analysis.

Brownlee, Fuller, and others, Chemistry of Common Things.

INORGANIC CONSTITUENTS OF FOODS

EXPERIMENT 36

Water in Foods

MATERIALS. White bread, milk, meat, potato.

APPARATUS.

Laboratory balances, drying oven, evaporating dish.

A. The Presence of Water in Foods.

How is the presence of water in food determined? (See Experiment 12 C.) Test four foods for water.

B. The Amount of Water in Foods.

1. To determine exactly how much water a substance contains it is weighed, then dried and weighed again. The loss in weight is the weight of the water that was in the substance. Divide the weight of the water by the weight of the substance before drying and multiply the result by 100 to give the per cent of water in the substance.

weigh both

Find the per cent of water in bread as follows: Label your evaporating dish with your name and weigh it. Obtain the largest cube of bread that will go into the dish and as carefully as you can on the laboratory balance. Place the dish and the bread in the drying oven for about six hours, keeping the temperature below 106° C. Why? When completely dry cool and weigh. Tabulate the results as follows:

2. From the table in the Appendix make a list of five foods which contain much water (80 %-100 %), five which contain a medium amount of water (15%-80%), and five containing very little water (less than 15 %).

3. What tissues of the body contain much water? What tissues contain the least water?

4. Of what use is water to the body?

Inorganic Salts in Foods (Mineral Matter or Ash)

MATERIALS. Bones that have soaked for at least two days in hydrochloric acid, ammonium hydroxide, milk, meat, potato,

bread. APPARATUS.

Porcelain crucibles, clay triangle, evaporating dish.

A. Inorganic Salts in Foods.

Inorganic salts do not burn; they remain as ash, when the organic matter of the food has been burned away.

1. To show the presence of inorganic salts in a food place about 1 gram of the food in a porcelain crucible and heat with the crucible inclined. In this way, heat milk, meat, potato, and bread.

(Four students may work together, the first heating milk,

the second meat, etc.

Each student should make observa

tions and reports on four foods.)

2. From the table in the Appendix make a list of foods. containing much mineral matter and a list of foods containing little or no mineral matter.

B. To Show the Presence of Inorganic Salts in Bones.

1. Clean a small bone by boiling in water. Place the clean bone in a beaker of hydrochloric acid and allow it to stand for two days. Explain the change that has taken place in the bone. Keep the bone.

2. Place 10 cc. of the clear liquid in an evaporating dish and evaporate to dryness. What is the dry residue that remains?

3. Prove the presence of calcium salts in the ash by dissolving it in 5 cc. of hydrochloric acid. Filter. Make the solution alkaline with ammonium hydroxide. What is the white precipitate chiefly?

4. What tissues of the body contain much mineral matter and what tissues very little?

CARBOHYDRATES

Carbohydrates are organic compounds which form the most important part of our foods. They contain no nitrogen (non-nitrogenous). They are composed of carbon, hydrogen, and oxygen, the hydrogen and oxygen usually being present in the proportion in which it is found in water, that is, twice as many atoms of hydrogen as oxygen. The starches and the sugars are the most important carbohydrates found in foods.

THE STARCH GROUP (C6H10O5)n

EXPERIMENT 38

Starch and Dextrin

MATERIALS. Corn starch, rice starch, wheat starch, potato starch, dextrin, concentrated sulfuric acid, Fehling's solution, dilute sulfuric acid, sodium carbonate, litmus paper, iodine solution, potato, meat, milk, apple, banana, nuts, rolled oats, raisins. APPARATUS. Test tubes, microscope, labels, asbestos mat. A. Properties of Starch.

1. Obtain about one gram of corn starch, rice starch, wheat starch, and potato starch in separate tubes. Is there any difference in the appearance of each?

2. Mount a few grains of each on microscope slides and draw the appearance of each under the high power.

3. Add 10 cc. of water to each tube. Shake the mixture well and then let it stand for one minute. Does starch dissolve in cold water?

4. Shake the mixture of corn starch and water again and then boil it for a few minutes. (Keep this for 9.)

5. Gently heat a little corn starch in a dry test tube until it becomes brown. What is formed? Taste it. Try the solubility of some pure dextrin in water. What is dextrin used for? Why is the brown crust of bread sweet?

6. Heat strongly one gram of starch in a dry test tube. What collects on the sides of the tube? Explain. What remains in the tube? What does this show about the composition of starch? Write an equation to show what took place.

7. Add a few drops of concentrated sulfuric acid to some dry starch in a test tube. Warm gently. Explain results. How does this also show the composition of starch?

8. Burn a small lump of starch on your asbestos mat. What products are found? Write an equation to illustrate.

9. To 5 cc. of starch paste prepared in (4) add 5 cc. of Fehling's solution and boil. Result? (To prepare Fehling's solution, see Appendix.)

10. To 10 cc. of starch paste add 10 cc. of dilute sulfuric acid. Boil for five minutes. Add solid sodium carbonate till the mixture is alkaline to litmus, then add Fehling's solution and boil. Result?

Note: If a red precipitate is not obtained, try again. The starch combines with a molecule of water to form glucose (grape sugar). Glucose is a reducing sugar and reduces the copper sulfate in the Fehling's solution to cuprous oxide. Cuprous oxide is the red precipitate. When a substance like starch takes up water and becomes a new substance, it is said to hydrolyze. The process is called hydrolysis. There are several ways of hydrolyzing substances: (1) By boiling with a dilute acid, (2) boiling with a base, (3) by means of an enzyme or ferment.

How is starch caused to hydrolyze? Could any acid be used other than sulfuric acid? Write this equation for the hydrolysis of starch and name each substance:

C6H10O5+H2O (by means of H2SO4) — C6H12O6.

B. The Iodine Test for Starch.

1. Obtain about 10 cc. of a solution of iodine in one of your clean test tubes. To some dry starch add about 1 cc. of iodine solution. Results?

2. To a test tube half full of water add two drops of cold starch paste. Shake well, then add about two drops of the iodine solution. Results? Boil till the color disappears, then cool again and the color will return if you have not boiled it too long. This is called the iodine test for starch.

3. To detect the presence of starch in foods the food should (1) be broken into small pieces or powdered. Why? (2)