concentrated hydrochloric acid. If action is slow, warm gently. When the effervescence is rapid, add 10 c.c. cold water.

EXPERIMENT XXII.

HYDROGEN CHLORIDE.

Apparatus. Same as in Experiment XXI..

Materials.

Sodium chloride, concentrated sulphuric acid, red and blue litmus paper, iron filings, silver nitrate solution, ammonium hydroxide solution, dilute hydrochloric acid, sodium chloride solution, calcium chloride solution.

a. Into a 100 c.c. flask with stopper and delivery tube as in Experiment XXI, put 5 to 7 c.c. water, and add carefully 20 c.c. concentrated sulphuric acid. Result? In diluting sulphuric acid always pour the acid into the water.

Caution.

b. Cool the diluted acid by holding the flask in a stream of running water. When the acid is cold, put into it about 15 grams sodium chloride.

c. Attach the stopper and the delivery tube, and place the flask on the wire gauze of a ring stand. Warm carefully with a small flame, and fill a dry bottle with the gas, it is hydrogen chloride, as in Experiment XXI, b.

You may know that the bottle is full when white fumes escape about the cardboard which covers the collecting bottle.

Fill, also, a dry test tube, and stopper both vessels.

HYDROGEN CHLORIDE.

35

d. Test the gas at the end of the delivery tube with strips of moistened red and blue litmus paper. Results? Blow your breath against the stream of gas. Result? Explain.

e. Now let the end of the delivery tube come just to the surface of 5 c.c. water in a test tube. Note the appearance of the water below the delivery tube. While the gas is coming off regularly, raise the test tube so that the end of the delivery tube is about 2 cm. below the water level. Do gas bubbles pass through the water? Why? Lower the test tube again until the delivery tube is at the surface, and let the gas run into the water five minutes. Is there any change in temperature?

Finally remove the delivery tube from the water and extinguish the flame. Save the liquid.

Lower the wire gauze so as to let the flask cool out of contact with the gauze.

f. Open the test tube of gas under water. Result? Explain.

g. Hold a burning match in the bottle of gas. Does the gas burn? Does it support combustion?

h. Test the liquid obtained in e with red and blue litmus. Compare results with those given by the gas. Add a drop of the liquid to 2 c.c. water, and taste a drop held on a stirring rod. Result?

i. Pour some of the liquid of e upon 1 c.c. iron filings in a test tube. Result? Does the gas burn?

The equation is: Fe+2HCl →→→→→→ FeCl2+?

j. Add a few drops of the liquid of e to 1 c.c. silver nitrate solution in a test tube. Result? The white precipitate is silver chloride, AgCl.

The equation is:

AgNO3 + silver nitrate

HCI

hydrochloric acid

? +?

To the precipitate add an excess of ammonium hydroxide solution, close the test tube with the thumb, and shake vigorously. Result?

k. Repeat j, using sodium chloride solution in place of hydrochloric acid. Result? Write the equation.

1. Repeat j again with calcium chloride solution in place of the acid. Results? Results? Conclusion? Equation? m. Note the white solid which separates when the flask becomes cool. It is chiefly sodium hydrogen sulphate, NaHSO4. Write the equation.

EXPERIMENT XXIII.

WEIGHT OF A LITER OF OXYGEN.

Apparatus. Hard-glass test tube, one-liter bottle, bent glass tubes, pinch-clamp, graduated cylinder, balances, large beaker or bottle.

Materials. Powdered, chemically pure potassium chlorate, dried at 120° C. Water at room temperature.

a. Set up the apparatus shown in Fig. 97. A is a hard-glass test tube that can be slipped tightly over a rubber stopper. B is a liter bottle fitted with a twohole rubber stopper. The longer tube reaches almost to the bottom of B, and is connected by a rubber tube with D, which reaches to the bottom of C. The rubber tube

WEIGHT OF A LITER OF OXYGEN.

37

may be closed by the pinch-clamp F. Almost fill the bottle B with water having the temperature of the room and then fill the tubes B,

and chlorate accurately on the balances, and record it. c. See that the stopper is pressed securely into the mouth of B, and then slip A carefully, but tightly, over its stopper. Now put about 50 c.c. water into C, raise C so that the water in B and C are at the same level, open the pinch-clamp one minute, and then close it. Then put C down on the table. Take D carefully out of C and get the volume of the water in C; then pour the water back into C, and put D in place. Now open the pinch-clamp, and hang it upon the glass tube to the left of F. Do not allow the lower end of D to get above the surface of the water in C. Why?

d. Heat the chlorate in A gently, beginning with a moving flame. The evolved gas forces water from B into C. When C is about full, stop heating, and let A cool to room temperature. Then raise B or C, as necessary, to make the water levels in both the same (be sure to keep the lower end of D under water), close the rubber

tube with the pinch-clamp, and get the volume of the water in C. This, minus the original volume, equals the volume of gas collected in B.

Find the barometric height, correct it for the pressure of water vapor (see Appendix), and find the temperature of the gas. Finally, weigh A.

e. Record your results thus:

Grams.

=

C.C.

=

° C.

mm.

C.C.

.. Wt. of 1 1. O at 0° C. and 760 mm.

EXPERIMENT XXIV.

PROPERTIES OF ACIDS.

Apparatus. - Stirring rod, test tubes or beakers.

Materials. Nitric, sulphuric, and tartaric acids; litmus paper, phenolphthalein solution.

a. Make a very dilute solution of sulphuric acid by adding three drops of the concentrated acid to 10 c.c. water in a clean vessel. By means of a clean stirring rod bring a drop of this solution to the tongue. What is its taste?

Note.

Whenever you taste a substance in this way always