a. To a 250 c.c. bottle containing enough zinc to cover the bottom fit a two-holed stopper. One of the holes is for a funnel tube reaching to within one-half a centimeter of the bottom of the bottle when the stopper is in place; the other hole contains a bent tube attached by a rubber connector to a delivery tube. The delivery tube reaches to a pneumatic trough containing two bottles filled with water and inverted.

b. Caution.

Keep all flames at least one meter (about three feet) away from apparatus in which hydrogen is made.

c. See that the stopper of the generating bottle is tight, and add enough of the dilute sulphuric acid to immerse the lower end of the funnel tube.

Tell what takes place in bottle, funnel tube, and pneumatic trough. Explain each phenomenon. If action is not vigorous add a few drops of copper sulphate solution. Result? If evolution of gas ceases or becomes slow before you are through, add more acid. The gas produced is hydrogen.

d. Fill the two bottles with the gas and refill them after using. Reject the first bottleful collected by turning it mouth upward. Why not use it? Why turn it mouth upward?

Keep the second bottle inverted and introduce into its middle part a burning pine splinter 15 to 20 cm. long. Hold the splinter steady 20 to 30 seconds. Result? Does the gas burn? Where? Does the splinter continue to burn in the hydrogen? Is hydrogen combustible or a supporter of combustion?

Turn a third bottle of the gas mouth upward one minute, and repeat the test with the burning splinter.

Results? From the result compare the specific gravity of hydrogen with that of air.

e. Place the mouth of a fourth bottle of gas over the mouth of an upright bottle of air. Hold the bottles together and reverse their positions. After one minute apply a lighted match to the lower bottle. Result? To the upper. Result? What conclusion as to the diffusibility of hydrogen?

f. Have a fifth (and last) bottle only half full of gas; incline it, and then raise it slowly from the water so that air displaces the remaining water. Carry bottle, mouth down, to a flame. Result? Explain difference between this result and the combustion of hydrogen free from air.

g. From the experiment tell whether hydrogen is very soluble in water, or not.

h. Pour the liquid and the unused zinc from the bottle into a beaker. If the zinc has all dissolved, or if there seems to be enough acid to dissolve all of it, add more zinc. Leave until action ceases.

i. Examine the beaker; has anything separated from solution? If so, re-dissolve it by heating the beaker on the wire gauze, and filter hot. (Care!)

Collect the filtrate in another beaker or an evaporating dish, and let it stand some hours. Result?

The substance you obtain is crystallized zinc sulphate.

EXPERIMENT IX.

BURNING OF HYDROGEN AND REDUCTION OF

OXIDES.

Apparatus. Hydrogen generating bottle of Experiment VIII, two-hole stopper, funnel tube, right-angle tube, rubber connector, a second right-angle tube of slightly larger diameter than the other, beaker, and test tube.

Materials. Zinc, dilute sulphuric acid, cupric sulphate solution, cupric oxide (in wire form if possible).

a. Arrange the apparatus of Fig. 95. Into the longer (horizontal) arm of the second right-angle tube (B)

A

B

FIG. 95.

put cupric oxide in wire form. To the zinc in the generating bottle (A) add a few drops of cupric sulphate solution, then dilute sulphuric acid. When the gas comes off readily, hold over the end of the exit tube (C) a cold, clean beaker. Does any deposit of moisture appear?

b. Over the end of C invert a test tube, and

after a minute carry it, mouth down, to a flame at least 4 feet away. Note what happens, and at once return the test tube, still mouth down, to the jet C. Continue until the hydrogen is lighted at C (consult § 50, pg. 41, of text). What is the color of the hydrogen flame at first?

EQUIVALENT WEIGHT OF MAGNESIUM.

17

After the end of C has become hot? For the reason, cf. § 411 of text. Hold a cold beaker over the hydrogen flame. Is there a deposit now? What is it? How was it formed?

c. While the hydrogen flame is burning, heat the tube at B, under the cupric oxide, first with a moving flame, then more strongly. Do not heat it enough to melt the glass.

What change occurs in the cupric oxide? What is the solid substance left? Is there any deposit in the tube? What is it? What was the source of the oxygen when hydrogen burned? When it was passed over cupric oxide? Define reduction.

EXPERIMENT X.

EQUIVALENT WEIGHT OF MAGNESIUM.

Apparatus. Balances, pneumatic trough, wide-mouth bottle (250 c.c.), graduated jar, glass or cardboard cover. Materials. Magnesium wire, dilute sulphuric acid.

a. The object of this experiment is to find how many grams of magnesium replace 1.008 grams of hydrogen. The resulting number is called the equivalent weight of magnesium. The weight of the hydrogen is calculated from the volume. The volume actually obtained is "reduced" to 0° C. and 760 mm. From this we get the weight, for 1 1. of hydrogen at 0° C. and 760 mm. weighs 0.09 gram (cf. Appendix v).

b. In a pneumatic trough containing water to the

depth of about 3 cm. place a piece of magnesium wire the exact weight of which is known. There should be not more than 0.2 gram.

Get the exact capacity in cubic centimeters of a widemouth bottle by filling it with water and pouring the water into a graduated vessel. The bottle should hold at least 250 c.c.

c. Half fill the bottle with dilute sulphuric acid, then add enough water to fill it, and invert it in the pneumatic trough as far from the magnesium as possible. See that the bottle is free from air bubbles. Now slide the mouth of the bottle, under water, over the magnesium. Result?

d. When all the metal has disappeared, let the collected gas cool to room temperature for 5 minutes. Then add water of room temperature to the bowl, if necessary, so that the level of water in bottle and bowl shall be the Why?

same.

Protect the bottle from the heat of the hand by grasping it with a towel; then slip under its mouth a glass or cardboard cover, and invert quickly, so as to lose none of the water in the bottle.

Bring a flame to the mouth of the bottle at once. Result?

The gas is hydrogen. The other product of the reaction is magnesium sulphate; it remains in solution.

Let your thermometer remain in the solution in the bottle for five minutes; then read it, and call this the temperature of the hydrogen. Also read the barometer. e. Get the volume of the water remaining in the bottle by means of a graduated vessel. volume of the hydrogen by difference.

Then obtain the From the reading