a. On a clean piece of writing paper mix carefully 6-8 c.c. powdered potassium chlorate with about 3 c.c. powdered manganese dioxide. If the substances are not found in powdered form in the laboratory, grind them separately, in clean mortars, before mixing.

b. Before you use the whole mixture, test the quality of a sample (1 c.c.) by heating it gently in an open test tube. If there is any evidence of violent combustion, or if large sparks appear, reject the mixture, and make a fresh one. A few small sparks indicate only traces of dust, etc.

c. If the mixture is satisfactory, put it into a test tube supported by a clamp attached to a ring stand. The test tube is then fitted with a one-holed stopper and a delivery tube reaching under water in a pneumatic trough.

Have 4 bottles filled with water and inverted in the trough.

To invert bottles in the trough without letting in air, fill them to overflowing with water, cover their mouths with slips of glass or cardboard, press the latter against the bottle, and invert quickly under water. Then remove the covers.

To remove a bottle full of gas from water, slip under the mouth of the bottle, under water, a glass or cardboard cover, and hold it in place as before. Leave a filled bottle with its mouth under water until used, if possible.

Whether a bottle of gas shall be placed upright or inverted upon the table depends upon the specific gravity of the gas.

d. Heat the test tube gently from the top of the mixture downward. Regulate the flame so as to keep the

evolution of gas steady, but not violent. Keep the flame in motion, so as not to soften the glass.

When the collecting bottles are full, first take the delivery tube out of the water, and then remove the flame. Why this precaution?

The gas is oxygen.

e. Into one bottle of the gas put a glowing splinter as in Experiment IV, c. Result? Gradually lower the splinter into the bottle until combustion stops. What becomes of the splinter? Of the oxygen?

To the contents of the bottle add 5 c.c. calcium hydroxide solution (lime-water), cover with the hand, and shake vigorously. Result?

N.B. Lime-water reacts with carbon dioxide to give a white, insoluble solid, calcium carbonate. This serves as a test for carbon dioxide. Where does the carbon of the carbon dioxide come from?

f. Note the odor of the gas in the second bottle. Then put into the bottle a deflagrating spoon containing burning sulphur. Light the sulphur by holding the spoon in a flame.

Have a cardboard cover with a small hole for the handle of the deflagrating spoon, and keep the bottle covered until combustion stops. Results?

What becomes of the sulphur? Of the oxygen? Note the odor of the gas now in the bottle. Does this gas support the combustion of a splinter? Try it. Name the gas. Add 5 c.c. of water to the bottle, shake it about, and then put in one piece each of red and blue litmus paper. Result?

g. Have the third upright on the table.

bottle of oxygen covered and set Draw aside the cover for a moment

while you pour in sand enough to cover the bottom of the bottle; then replace the cover.

Melt some sulphur in a deflagrating spoon, and dip into it one end of a piece of iron picture cord. Light the sulphur tip, and at once hold the iron wire in the bottle of oxygen. Result? Keep the wire in the gas until action ceases. Describe the product and name it. Why was the iron tipped with sulphur?

h. Hold a piece of magnesium wire or ribbon by means of iron tongs, or make a hook upon it, and hang it on the reverse end of a file. Light it in the Bunsen flame, and hold it in the fourth bottle of oxygen. Result? Name and describe the product. Add a few drops (not more) of water to the product in the bottle, and then bring into contact with it one piece each of red and blue litmus paper. Let them remain some time.

one is changed? Compare with the result in f.

Which

EXPERIMENT VI.

PER CENT OF OXYGEN IN POTASSIUM CHLORATE.

Apparatus. Hard glass test tube, Bunsen burner, clamp, and ring stand.

Materials. Pure, powdered potassium chlorate which has been dried in an air bath at 120° C.

a. The object of this experiment is given in the title. It is attained by decomposing completely a weighed amount of pure, dry potassium chlorate and weighing the potassium chloride that remains. The material lost is oxygen.

b. Weigh a clean, dry hard-glass test tube accurately,

and put into it about 5 c.c. (a layer 1 inch thick) of the potassium chlorate. Wipe off any particles that may adhere to the mouth of the test tube. Weigh the test tube and chlorate accurately, and record the weights as directed in § d.

c. Support the test tube of b by means of a clamp and a ring stand, keeping the open end of the test tube a little higher than the closed one. Have the clamp near the open end. Begin to apply heat cautiously, with a small, moving flame. Then heat more strongly, until all the chlorate melts, and the melted substance is in effervescence. Do not let the effervescence become so rapid that much white smoke is driven out of the test tube. When all effervescence seems to have stopped, heat more strongly still, so that every part of the contents is completely melted and ceases to effervesce. Then let the tube cool, weigh it, and record the result. To make certain that the decomposition is complete, heat the tube again, cautiously at first, then strongly, and weigh the tube once more. Continue this until there is no difference between successive weighings. We call this "heating to constant weight." Use the last weight in calculating results.

d. Record the results as follows:

EXPERIMENT VII.

KINDLING TEMPERATURE.

Wire gauze at least 15 cm. square, Bunsen

Material. - Matches.

a. Hold the wire gauze, by means of your tongs, 7 cm. above the Bunsen burner. Have the holes of the burner open as for the Bunsen flame. Now turn on the gas and bring a burning match from above down to the center of the gauze. Result?

Why does not the gas below the gauze take fire? Is there gas below the gauze? Prove it.

b. Let the gauze cool; and then bring it down upon the Bunsen flame until the gauze is 6 to 7 cm. above the top of the burner. Result? Hold the gauze in place until it becomes red hot. Result? Explain.

EXPERIMENT VIII.

HYDROGEN.

Apparatus. Generating flask, or bottle of 250 c.c. capacity, two-holed stopper, funnel tube, right-angled tube, rubber connector, delivery tube, pneumatic trough, squares of glass or of cardboard, two or more wide-mouth collecting bottles (250 c.c.).

Materials. Zinc, dilute sulphuric acid (one part by volume of acid to four volumes of water), pine splinter, cupric sulphate solution.