moving the flame back and forth below it. Is there a residue?

2. Now place a few drops of faucet water on the glass and evaporate. A residue indicates something dissolved in the water. Does the city water contain dissolved salts?

3. What other impurities besides dissolved salts may a water contain?

B. Impurities Removed by Filtration.

1. To some water add dirt, some table salt, and some potassium permanganate to give it color. Place a filter in a funnel and into this pour a thin paste of bone black and water. When this has settled, pour on to it some of the turbid, salty, colored water. Is the turbidity removed? Is the color removed? Is the salt removed? Test this by evaporating a few drops on a watch crystal as before. Would dangerous germs or poisonous organic matter be removed? 2. What impurities are removed by filtration?

C. Impurities Removed by Distillation.

(Instructor's Experiment.)

1. Place about 100 cc. of the same turbid water in a roundbottomed distilling flask and connect the flask to the condenser. Why should the water enter the lower opening of the condenser jacket? The water flows out of the upper opening through a rubber tube to the sink. Heat the flask over a screen until the water boils. The steam from the boiling water is condensed in the cool condenser tube and collected in a flask. The condensed liquid is called the distillate. The process is distillation.

2. Note the color and taste of the distilled water. Test for salt by means of the watch glass as before.

3. Where is the salt and coloring matter? What impuri

ties may be removed by distillation? What impurities may not be removed in this way?

4. Which is the better water to drink, filtered water or distilled water? Give all the reasons that you can for your

answer.

5. What is the source of the drinking water in your city? What impurities are present in this water? What attempts, if any, are made by the city to remove them? How could you make the water more fit for drinking purposes at home?

EXPERIMENT 16

Properties of Hydrogen Peroxide

MATERIALS. Hydrogen peroxide, litmus paper, manganese dioxide, dark hair, ammonium hydroxide.

APPARATUS. Large test tube, splint, filter paper funnel.

A. Properties of Hydrogen Peroxide.

1. What is the formula of hydrogen peroxide? How does it differ in composition from water?

2. What is the hydrogen dioxide sold by druggists? 3. Place 5 cc. of hydrogen peroxide in a large test tube. Test with a small piece of litmus paper. Explain.

4. Add 2 grams of powdered manganese dioxide. Thrust a glowing splint into the tube. What gas is given off? Write the equation. Filter the mixture remaining in the tube. What is the residue? What was the purpose of the manganese dioxide?

5. Why should bottles of hydrogen peroxide be kept tightly stoppered? Why are the bottles always dark in color?

6. Why are the corks of the hydrogen peroxide bottles so white?

B. Uses of Hydrogen Peroxide.

1. Wash some dark hairs free from oil, then immerse them for one hour in 10 cc. of hydrogen peroxide made alkaline with ammonium hydroxide. Remove them and allow them to dry. Result? Hydrogen peroxide is used to bleach wool and silk.

2. Give some of its uses as a disinfectant.

IV. NITROGEN AND THE AIR

EXPERIMENT 17

Preparation and Properties of Nitrogen

MATERIALS. Phosphorus, charcoal, pine splints, 4 g. ammonium chloride, and 8 g. sodium nitrite mixed.

APPARATUS. Wide-mouthed bottle, cover glasses, glass pneumatic trough, 250 cc. flask, one-hole stopper, delivery tube, troughs, 2 gas bottles, ring stand, gauze.

A. Nitrogen from the Air. (Instructor's Experiment.)

Nitrogen and oxygen are the chief gases of the air. If phosphorus is burned in a bottle of air, it will combine with the oxygen, forming phosphorus pentoxide. If there is water in the bottle, the phosphorus pentoxide will dissolve in the water and nitrogen will be left in the bottle.

1. Pin a piece of phosphorus about the size of a pea to a piece of charcoal. Float the charcoal on the water in the glass trough. Light the phosphorus and quickly cover it with a large, wide-mouthed bottle. Keep the neck of the bottle pressed well down into the water. bottle filled when it was placed over the burning phosphorus? What is the "smoke" that is formed as the

With what was the

phosphorus burns? What constituent of the air is being removed?

2. Allow the bottle to stand till the "smoke" has dissolved in the water and the gas in the bottle is clear, then make the water level the same inside as outside the bottle. Why has the water risen in the bottle? The gas remaining is chiefly nitrogen. About what part of the air is nitrogen?

3. Cover the mouth of the bottle with a glass plate and invert, taking care not to lose any of the water that has risen in the jar. What are the physical properties of nitrogen in the jar? What are the physical properties of the nitrogen in the air? Is the nitrogen in the bottle pure? Why?

Does it

4. Thrust the burning splint into the bottle of nitrogen. Result? Repeat, using phosphorus. Result? burn? Does nitrogen support combustion?

B. Preparation of Pure Nitrogen. Note: Instructor's Experiment, unless Class Is Very Small.

1. Obtain a mixture of 4 grams of ammonium chloride and 8 grams of sodium nitrite. Place this in a 250 cc. flask and add 25 cc. of water. Fit a one-hole rubber stopper and a delivery tube to the flask in order that the gas may be collected over water as in case of oxygen. Clamp the flask to the ring stand over a wire gauze and heat very gently by moving the burner about with the hand. As soon as action begins, stop heating. If the action becomes too violent, lower the wire gauze and raise a bowl of water until the flask is immersed in it and cooled.

When the air is expelled from the flask (about one minute), fill two gas bottles with nitrogen.

2. The reaction that takes place in the preparation of pure nitrogen may be expressed in two equations. (1) The

ammonium chloride and the sodium nitrite react to form ammonium nitrite and sodium chloride :

NH4Cl+NaNO2 →→ NH4NO2+NaCl

(2) The ammonium nitrite then decomposes into water and nitrogen:

Write these two equations for the preparation of nitrogen, naming all substances used and formed.

3. Using one bottle of the gas, note its physical properties, i.e. its color, odor, taste.

Is it soluble in water?

Is it heavier or lighter than air? (See Appendix.)

4. Into the other bottle of gas thrust a burning splint. Does nitrogen burn?

Does nitrogen support combustion?

MATERIALS.

EXPERIMENT 18

The Composition of the Air

Phosphorus, splint, limewater, calcium chloride. APPARATUS. Glass trough, graduated tube 100 cc. or 250 cc., wire, cover glasses, beaker, long glass elbow, test tube, gas bottle.

A. The Per Cent of Nitrogen and Oxygen in the Air. (Instructor's Experiment.)

1. Half fill a glass trough or battery jar with water. Invert into the jar a graduated tube (about 100 cc. or 250 cc.). Adjust so that the water within and without the tube stands at the same level. Why? Note the volume of air in the tube. 2. Place a piece of phosphorus on the tip of a wire and insert in the tube. Push up the wire till the phosphorus