Human Foods and Their Nutritive Value

by Harry Snyder

Experiment No. 46

Organic Matter in Water

Pour into the evaporating dish 100 cc. H₂O 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 H₂O add a few drops of HNO₃ and 2 cc. of AgNO₃. A white precipitate indicates the presence of chlorids, usually in the form of sodium chlorid.