LABORATORY DIRECTIONS.

(For the Student.)

1. Provide yourself with an apron and a pair of sleeves (rubber is the best material for these); also with soap and towel, and a white cloth about a yard square. The cloth is to be used for wiping apparatus.

2. Work by yourself; and give your own descriptions, observations, and calculations, not those of another.

3. Record at once all the observations you make in connection with an experiment. See that your notes contain the answer to every question, direct or implied, that occurs in the laboratory exercise. Write neatly and distinctly. If the notes of two experiments occur on the same page, separate them by at least two centimeters of space.

4. Have a place for everything. Throw away nothing until you are sure you are through with it. Throw nothing but liquids into the sink. Put other waste materials into the proper receptacle.

5. If an experiment is unsatisfactory, repeat it until you are successful; but first learn the probable cause of your error.

6. When you enter the laboratory, examine your table, and see that everything has been left as it should be by the persons who share the table with you. If anything is wrong, report the fact at once to the instructor.

When you leave, see that the water and the gas are turned off, and that everything on your table is in good order.

LABORATORY EXERCISES.

EXPERIMENT I.

THE BUNSEN BURNER.

Apparatus. Bunsen burner, test tube, test-tube holder (see note below).

a. Examine carefully the Bunsen burner on your desk. Take it apart, and draw a sketch of each part.

b. Put the burner together, close the holes at the base, and connect with gas supply.

To light the burner, turn on the gas and then hold a lighted match near the side of the burner and about onehalf a centimeter below its mouth. Note the character of the flame; is it luminous or not? Now open the holes carefully until the luminous region has just disappeared. This is the "Bunsen " flame. For most work it should be 7 to 10 centimeters (3 to 4 inches) high. The holes of the burner should be open far enough to prevent a deposit of soot upon the object heated, but not far enough to cause the flame to make a noise.

c. Introduce quickly into the center of the Bunsen flame, one-half a centimeter above the burner, the head end of a match. Result? Is the gas in this region burning?

To heat an object effectively, place it higher up in the flame; the best place is just above the apex of the dark, inner cone of unburned gas. Locate this region.

d. Put 5 c.c. water into a test tube, and make a note of the height of the column of water in centimeters. Whenever you are asked to take 2, 5, 10, etc., cubic centimeters of anything, refer to this experiment, and use the length of the column just measured as your unit.

e. Heat the water in the test tube to boiling. To do this properly have the outside of the tube dry; hold the tube in the holder, and incline the tube at an angle of about 45° to the table top. Then introduce the bottom of the tube into the effective region (cf. c) of the flame. Heat only the part of the tube containing the liquid; if the flame strikes the glass above the liquid level, the tube may crack.

Do not hold the tube still, but move it gently in the flame. When boiling begins, raise the tube a little above the flame,- always keeping it inclined, so that the water may not "boil over."

f. These directions are general, and will apply whenever you heat liquids in test tubes.

Note. A

very convenient test-tube holder can be made by folding a piece of writing paper twice, so as to produce a strip about 1 cm. wide and 10 to 15 cm. long. This is placed about the tube like a holder. The free ends are held together close to the tube.

MANIPULATING GLASS TUBING.

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EXPERIMENT II.

MANIPULATING GLASS TUBING.

Apparatus.

Bunsen burner, "wing-top" or illuminating

gas burner, file, blast-lamp.

Materials.

Piece of soft glass tubing more than 15 cm. long, one of ignition tubing 18-20 cm. long.

a. Cut off a piece of glass tubing 15 cm. long. To do this, make on the tubing a file mark in a plane perpendicular to the length of the tubing; grasp the tube in both hands, and place the thumb nails together opposite the scratch. By pushing gently with the thumbs and at the same time pulling with the hands you will succeed in breaking the tubing so that the ends are fairly regular. b. Round off ("fire-polish ") both ends of the 15 cm. tube by turning them about in the Bunsen flame until the edges become red hot. Let the ends cool.

c. Bend the 15 cm. tube at its middle into the form of a right angle. For this purpose use a flat Bunsen flame produced by a wing-top" attachment

illuminating flame.

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or a flat

Take the tube in both hands, one at each end, and hold its central part lengthwise with and over the flat flame. At the same time twirl the tube between thumbs and forefingers. Then lower the tube- keep turning it into the upper part of the flame, and heat until you find that the glass is fairly soft. Then bend gently to a right angle.

d. If you used the Bunsen flame, anneal the glass at the bend by closing the holes of the burner and allowing