Human Foods and Their Nutritive Value Part 21

Examine Rio, Java, and Mocha coffee berries. Describe each. Note the characteristics of each kind of coffee berry.

Experiment No. 42

Detecting Chicory in Coffee

Fill a beaker with water and place about a teaspoonful of ground coffee on the surface. If much of the ground material sinks and it imparts a dark brown color to the lower portion of the liquid, it is an indication of the presence of chicory. Pure coffee floats on water. Chicory has a higher specific gravity than coffee.

1. How may the presence of chicory in ground coffee be detected? 2. Why does coffee float on the water while chicory sinks? 3. What effect does chicory have upon the color of water?

Experiment No. 43

Testing Hard and Soft Waters

Partially fill a large cylinder with very hard water. This may be prepared by dissolving 0.1 to 0.2 gm. calcium chloride in 500 cc. of ordinary water. Add to this a measured quant.i.ty of soap solution. Mix well and notice how many cubic centimeters of soap solution must be used before a permanent lather is formed, also notice the precipitate of "lime soap." Repeat this experiment, using either rain or distilled water, and compare the cubic centimeters of soap solution used with that in former test. Repeat the test, using tap water.

Soap Solution.--Sc.r.a.pe 10 gms. of castile soap into fine shavings and dissolve in a liter of alcohol, dilute with 1/3 water. Filter if not clear and keep in a tightly stoppered bottle.

1. Why is more soap required to form a lather with hard water than with soft water? 2. What is meant by "lime soap"? Describe its appearance. 3.

How may hard waters be softened for household purposes?

Experiment No. 44

Solvent Action of Water on Lead

Put 1 gm. of clean bright lead shavings into a test tube containing 10 cc. of distilled water. After 24 hours decant the clear liquid into a second test tube, acidify slightly with HCL, and add a little hydrogen sulphid water. A black or brownish coloration indicates lead in solution.

(Adapted from Caldwell and Breneman, "Introductory Chemical Practice.")

Under what conditions may lead pipes be objectionable?

Experiment No. 45

Suspended Matter in Water

Place a drop of water on the microscopical slide, cover with cover gla.s.s, and examine with the microscope. Note the occurrence and appearance of any suspended matter in the water.

Experiment No. 46

Organic Matter in Water

Pour into the evaporating dish 100 cc. H_{2}O and evaporate to dryness over the sand bath. Ignite the solids. If the solids blacken when ignited, the water contains organic matter.

Experiment No. 47

Deposition of Lime by Boiling Water

Boil for a few minutes about 200 cc. of water in a flask. After the water is cool, note any sediment of lime or turbidity of the water due to expelling the carbon dioxid.

1. What is meant by a "hard" water? 2. What do the terms "temporary" and "permanent" hardness of water mean? 3. What acts as a solvent of the lime in water? 4. Why does boiling cause the lime to be deposited?

Experiment No. 48

Qualitative Tests for Minerals in Water

Test for Chlorids.--To 10 cc. of H_{2}O add a few drops of HNO_{3} and 2 cc. of AgNO_{3}. A white precipitate indicates the presence of chlorids, usually in the form of sodium chlorid.

Test for Sulphates.--To 10 cc. of water add 2 cc. of dilute HCl and 2 cc. of BaCl_{2}. A cloudiness or the formation of a white precipitate indicates the presence of sulphates.

Test for Iron.--If a brown sediment is formed in water exposed to the air for some time, it is probably iron hydroxid. To 10 cc. of the water add a few drops of HNO_{3}, heat, and then add 1/2 cc. of NH_{4}CNS. A red color indicates the presence of iron.

Test for CaO and MgO.--To 10 cc. of H_{2}O add 5 cc. NH_{4}OH. If a precipitate forms, filter it off, and to the filtrate add 3 cc. NH_{4}Cl and 5 cc. (NH_{4})_{2}C_{2}O_{4}. The precipitate is CaC{2}O_{4}, and the filtrate contains the magnesia. Filter and add 5 cc. Na_{3}PO_{4} to precipitate MgNH_{4}PO_{4}.

1. How would you test a water to detect the presence of organic matter?

2. Name some mineral impurities often found in water. 3. Describe the test for chlorids; for sulphates; for iron; for lime; for magnesium. 4.

Of the two cla.s.ses of impurities found in water, which is the more harmful? 5. Name three ways of purifying waters known to be impure, and tell which is the most effectual.

Experiment No. 49

Testing for Nitrites in Water

To 50 cc. of water in a small beaker add with a pipette 2 cc. of naphthylamine hydrochloride and then 2 cc. of sulphanilic acid. Stir well and wait 20 minutes for color to develop. A pink color indicates nitrites.

REAGENTS USED

Sulphanilic Acid.--Dissolve 5 gm. in 150 cc. of dilute acetic acid; sp. gr. 1.04.

Naphthylamine Hydrochloride.--Boil 0.1 gm. of solid [Greek: a]-amidonaphthaline (naphthylamine) in 20 cc. of water, filter the solution through a plug of absorbent cotton, and mix the nitrate with 180 cc. of dilute acetic acid. All water used must be free from nitrites, and all vessels must be rinsed out with such water before tests are applied.

1. Would a water showing the presence of nitrites be a safe drinking water? Why? 2. What are nitrites? 3. What does the presence of nitrites indicate? 4. Are small amounts of nitrites, when not a.s.sociated with bacteria, injurious?

REVIEW QUESTIONS

CHAPTER I

GENERAL COMPOSITION OF FOODS