Human Foods and Their Nutritive Value Part 20

Experiment No. 31

Testing Baking Powders for Alum

Place about 2 gms. of flour in a dish with 1/2 gm. baking powder. Add enough water to make a dough and then 2 or 3 drops of tincture of logwood and 2 or 3 drops of ammonium carbonate solution. Mix well and observe; a blue color indicates alum. Try the same test, using flour only for comparison.

1. How do you test a baking powder for alum? 2. What difference in color did you observe in the test with the baking powder containing alum and in that with the flour only? 3. Why is the (NH_{4})_{2}CO_{3} solution used?

Experiment No. 32

Testing Baking Powders for Phosphoric Acid

Dissolve 1/2 gm. of baking powder in 5 cc. of H_{2}O and 3 cc. HNO_{3}.

Filter and add 3 cc. ammonium molybdate. Heat gently. A yellow precipitate indicates phosphoric acid.

1. How do you test a baking powder for phosphoric acid? 2. What is the yellow precipitate obtained in this test?

Experiment No. 33

Testing Baking Powders for Ammonia

Dissolve 1/2 gm. of material in 10 cc. water; filter off any insoluble residue and to the filtrate add 2 or 3 cc. NaOH and apply heat. Test the gas given off with moistened turmeric paper. If NH_{3} is present, the paper will be colored brown. Do not allow the paper to come in contact with the liquid or sides of the test tube. (Perform the tests on two samples of baking powder.)

1. How do you test a baking powder for ammonia? 2. Why do you add NaOH?

3. Why must you be careful not to let the turmeric paper touch the sides of the test tube or the liquid?

Experiment No. 34

Vinegar Solids

Into a weighed aluminum or porcelain dish pour 10 cc. of vinegar. Weigh and then evaporate over boiling water. To drive off the last traces of moisture dry in the water oven for an hour. Cool and weigh. Calculate the per cent of solids. Observe the appearance of the solids. Test both samples and compare.

1. How may the per cent of solids in vinegar be determined? 2. Describe the appearance of the solids from the good and from the poor sample of vinegar. 3. What is the legal standard for vinegar solids in your state?

Experiment No. 35

Specific Gravity of Vinegar

Pour 170 cc. vinegar into 200 cc. cylinder. Place a hydrometer for heavy liquids (sp. gr. 1 to 1.1) in the cylinder. Note the depth to which it sinks and the point registered on the scale on the stem. Note temperature of vinegar. Record specific gravity of vinegar.

1. What effect would addition of water to vinegar have upon its specific gravity? 2. What effect would addition of such material as sugar have upon specific gravity? 3. Why should the specific gravity of vinegar be fairly constant? 4. What would be the weight of 1000 cc. of vinegar calculated from the specific gravity?

Experiment No. 36

Acidity of Vinegar

Into a small beaker pour 6 cc. of vinegar and 10 cc. of water and a few drops of phenolphthalein indicator. Run in standard KOH solution from a burette until a faint pink tinge remains permanently. Note the number of cubic centimeters of KOH solution required to neutralize the acid.

Divide this number by 10, which will give approximately the per cent of acetic acid.

1. How may the per cent of acidity of vinegar be determined? 2. Why was phenolphthalein used? 3. Why was KOH used? 4. What acids does vinegar contain? 5. What is the legal requirement in this state for acetic acid in vinegar? 6. How did the acidity you obtained compare with this legal requirement?

Experiment No. 37

Deportment of Vinegar with Reagents

To 10 cc. of vinegar in a test tube add 8 or 10 drops of lead sub-acetate and shake. Observe the precipitate. Lead sub-acetate precipitates mainly the malic acid which is always present in cider vinegar.

1. How may the presence of malic acid in a vinegar be detected? 2.

Describe the precipitate. 3. What does malic acid in a vinegar indicate?

Experiment No. 38

Testing Mustard for Turmeric

Place 1 gm. of ground mustard on a small watch gla.s.s and moisten slightly with water. Add 2 or 3 drops of NH_{4}OH, stirring well with a gla.s.s rod. A brown color indicates turmeric present in considerable quant.i.ty.

Test a sample of good mustard and one adulterated with turmeric and compare the results.

Experiment No. 39

Examination of Tea Leaves

Soak a small amount of tea and unroll 8 or 10 of the leaves. Make a drawing of a tea leaf. Observe the proportion of stems in each of three samples of tea; also the relative proportion of large and small leaves.

Observe if the leaves are even as to size and of a uniform color.

Experiment No. 40

Action of Iron Compounds upon Tannic Acid

Make an infusion of tea by placing 3 gms. of tea in 100 cc. of hot water and stirring well. Filter off some of the infusion and test 5 cc. with ferrous sulphate solution made by dissolving 1 gm. FeSO_{4} in 10 cc.

H_{2}O and filtering. Note the result.

1. What change in color did you observe when the ferrous sulphate solution was added to the tea infusion? 2. What effect would waters containing iron have upon the tea infusion?

Experiment No. 41

Identification of Coffee Berries