PHYSICAL PROPERTIES OF WATER.

19

of the barometer, in millimeters, subtract the "tension of water vapor," to get the partial pressure of the dry hydrogen, and then reduce the volume of the hydrogen to standard conditions.

f. Calculate the weight of the hydrogen, and solve the following proportion for x, the equivalent weight of magnesium.

Wt. of magnesium: Wt. of hydrogen :: x: 1.008.

Vol. of dry hydrogen at 0° C. and 760 mm.

C.C.

Wt. of dry hydrogen

Equivalent weight of magnesium=

g.

EXPERIMENT XI.

PHYSICAL PROPERTIES OF WATER.

Apparatus. Ring stand, wire gauze, 100 c.c. flask, one-hole cork stopper, doubly bent delivery tube, test tube, beaker, Bunsen burner, thermometer, evaporating dish.

Materials. Hydrant or well water, distilled water, salt, crushed or chipped ice.

a. Distillation of Water. Set up the apparatus of Fig. 96. Half fill the flask with hydrant water, support it on the wire gauze, and attach the doubly bent delivery tube. This reaches to a test tube standing in a beaker

FIG. 96.

(or bottle) of cold water. The test tube serves as both condenser and receiver. Distill the water until the distillate half fills the test tube. Taste the distilled water. Evaporate 5 c.c. of it to dryness in a clean evaporating dish. Note if there is a residue, and its amount. For comparison, evaporate 5 c.c. of hydrant water to dryness, and give the result. Define distillation.

b. Boiling Point of Water. Support a flask securely (use clamp or extra ring) on the wire gauze of a ring stand, fill it one third with distilled water, and boil the water. Get the temperature of the boiling water by immersing the bulb of the thermometer in it. Do not read the temperature until it is constant. The bulb must be completely immersed. Now wipe the bulb of the thermometer dry, and hold the bulb in the escaping steam about 2-3 cm. above the level of the water. Compare the two temperatures, and write them down.

Add more distilled water, if necessary, and one-third of a test tube of salt. Boil the salt water, and get its temperature. Also wipe the bulb of the thermometer

CHEMICAL PROPERTIES OF WATER.

21

perfectly clean and dry, and get the temperature of the escaping steam. Give the results.

c. Melting Point of Ice; a Freezing Mixture. Into a 50 c.c. beaker put about 30 c.c. of crushed or chipped ice, and stir it with the bulb end of the thermometer. Have the bulb completely immersed. Give the exact reading as shown by your thermometer. Is your thermometer correctly graduated? Now add half a test tube of salt to the crushed ice, and stir the mixture with the thermometer. What is the temperature? Will any other substances give freezing mixtures with ice? Consult text.

EXPERIMENT XII.

CHEMICAL PROPERTIES OF WATER.

Apparatus. Tongs or forceps, evaporating dish, small wide-mouth collecting bottle, glass square.

Materials. Sodium, water, blue and red litmus paper, solid sodium hydroxide, quicklime, anhydrous cupric sulphate.

a. Action of Sodium upon Water.

Caution. Do not handle sodium with wet hands, or with wet forceps. Do not put sodium into the waste jar. On no account leave any sodium on or about your desk or in your locker. Sodium is usually kept under kerosene or ligroin (cf. § 525 of text).

What is the appearance of a freshly cut surface of sodium? Is sodium hard or soft? Heavy or light?

Fill your smallest gas-collecting bottle three-fourths full of water, and cover it with a glass square. Draw

aside the cover, drop in a small piece of sodium (not over 8-10 cubic millimeters in volume: size of a wheat grain), and cover it at once. Note the action. When the sodium has disappeared, apply a lighted match to the bottle. Result? Result? What gas is formed when sodium reacts with water? Test the solution by rubbing it between the fingers. Result? If you get no decided effect, add a second piece of sodium (dry hands) exactly as you did the first, and repeat the test.

Put one piece each of red and blue litmus paper into the solution, and give the results. Compare with Experiment V, §§ f and h.

b. Add a small piece (same size as sodium used) of sodium hydroxide to 5 c.c. of water. Test the resulting solution with the fingers and with litmus, and compare the effects with those of a. Conclusion?

c. Action of Water with Quicklime. In an evaporating dish treat a lump of quicklime about the size of a small hickory nut, or a large cherry, with water, as long as the water is completely absorbed. Do not have an excess of water. Note the result after a few minutes. If no result appears, try the effect of warming the dish slightly. If there is still no result, repeat the experiment with a second lump of quicklime. Use the quicklime prepared from marble, if possible.

How is commercial quicklime made? Of what elements is it composed? What change takes place in slaking it? For what is it used? Consult text for

answers.

d. Action of Water with Anhydrous Cupric Sulphate. Compare the colors of blue vitriol and anhydrous cupric sulphate. To about 1 c.c. of anhydrous cupric sulphate

EQUIVALENT WEIGHTS.

23

held in the palm of your hand add one or two drops of water. What two results do you notice? What is the difference, as shown by this experiment, between blue vitriol and cupric sulphate?

EXPERIMENT XIII.

EQUIVALENT WEIGHTS OF MAGNESIUM AND OXYGEN.

Apparatus. - Evaporating dish, watch glass, evaporating apparatus (cf. b), tongs.

Materials. Magnesium wire or ribbon, dilute nitric acid.

a. The object of this experiment is to determine the number of grams of magnesium that combine with 8 grams of oxygen. The method used is to convert the magnesium into magnesium nitrate (cf. § 227 of text), and then to decompose the magnesium nitrate by heat (cf. § 230 of text). The residue is magnesium oxide.

In a weighed porcelain evaporating dish weigh out accurately about 0.5 g. of magnesium wire or ribbon. Provide the evaporating dish with a watch glass cover to prevent spattering. Draw this aside slightly, and add dilute nitric acid, a few drops at a time, until the metal has dissolved. Rinse the under side of the watch glass with 10 c.c. of water, collecting the rinsings in the evaporating dish. Remove the watch glass cover when evaporating in b.

b. Evaporate the solution of magnesium nitrate (on a water bath or steam bath if possible; otherwise on a wire gauze) until the residue is syrupy. Be careful to