avoid loss. Further evaporation over a flame generally causes spattering; but the heating may be continued safely if the flame is applied from above. Do this as follows:

Hold the evaporating dish by means of iron or brass tongs grasped in the left hand, and carefully move the dish about, so that the syrupy liquid is spread in a thin layer over the sides of the dish, but not nearer to the edge than one centimeter. At the same time hold the Bunsen burner in the right hand, move the flame gently round and round, and direct it upon the contents of the dish. By careful manipulation the magnesium oxide may be obtained as an opaque powder. When the decomposition of the nitrate seems complete, apply the flame from below again. Heat the dish to faint redness for five minutes, cool it, and get its weight. Record your weights as in Experiment VI.

To make sure that the dish is at constant weight, heat it carefully once more to redness, let it cool, and weigh it. If there is a loss, repeat the heating. Record the final weight.

c. Get the weight of the oxygen that combined with the magnesium. Then solve the following proportion for x:

Wt. of magnesium: wt. of oxygen :: x: 8.

Compare the equivalent of magnesium thus obtained with that obtained in Experiment X. What is the correct amount? What quantities of hydrogen and of oxygen are equivalent to this weight of magnesium? In what proportion, by weight, are they combined in water?

PRECIPITATION.

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EXPERIMENT XIV.

SOLUTION AND CRYSTALLIZATION.

Apparatus. Beaker (50 c.c.), stirring rod.

Materials. Potash alum, crystallized cupric sulphate (blue vitriol).

a. Put 20 c.c. water into a beaker, add 10 grams powdered alum, and stir two minutes with the stirring rod. Does all the alum dissolve?

b. Heat the beaker carefully on the wire gauze, stirring the contents. Result? Conclusion.

c. Set the beaker with the hot solution in cold water, and stir rapidly until solution cools. Result?

d. Dry the outside of the beaker, and heat again as in b. Result? Let the solution stand undisturbed until it is cold. Result? Compare with c, and account for the difference.

e. Repeat a, b, c, and d, with 20 c.c. water and 15 grams powdered blue vitriol. Results?

EXPERIMENT XV.

PRECIPITATION.

Apparatus. Test tubes.

Materials. Solutions of lead nitrate, potassium chromate, barium chloride, and calcium sulphate. Dilute sulphuric acid; alcohol.

a. To 5 c.c. of lead nitrate solution in a test tube add an equal volume of potassium chromate solution. Result? Let tube stand ten to fifteen minutes. Result?

The precipitate is lead chromate.

b. Repeat a, putting together hot barium chloride solution and dilute sulphuric acid. Result after ten to fifteen minutes? The precipitate is barium sulphate.

c. To 2 c.c. calcium sulphate solution add an equal volume of alcohol. Result? The precipitate is calcium sulphate.

Note.

-The insoluble solids formed in a and b are not the only products of these reactions; the other products are, however, soluble.

EXPERIMENT XVI.

SOLUBILITY OF POTASSIUM CHLORIDE.

Apparatus. Steam bath, water bath, or wire gauze; evan orating dish, balances.

Materials. Powdered potassium chloride, distilled water.

a. Make a saturated solution of potassium chloride by shaking 12 grams of the powdered substance in a clean flask with 25 c.c. distilled water at the temperature of the room. Continue shaking every little while for fifteen minutes. Record the temperature of the solution, and then weigh out accurately into your evaporating dish about 20 grams of the solution. Now evaporate (see b) the water until the residual potassium chloride is perfectly dry, and get its weight. From the results

WATER OF CRYSTALLIZATION.

27

calculate how much potassium chloride will dissolve in 100 grams of water at the room temperature.

b. If possible, evaporate the solution of a on a steam or water bath. If this is impossible, evaporate slowly and carefully on wire gauze, so as to avoid any loss by spattering.

c. Record your results thus:

... Wt. of water found: Wt. KCl found :: 100 grams : x.

EXPERIMENT XVII.

WATER OF CRYSTALLIZATION.

Apparatus. Test tubes, iron saucer (sand bath).

Materials. Crystals of zinc sulphate, of potash alum (potassium aluminum sulphate), and of cupric sulphate.

a. Place a few crystals of zinc sulphate in a dry test tube, and warm gently. Results? Is there evidence of water? Where?

b. Repeat a, using a crystal of potash alum. Results? c. Note the taste of another crystal of potash alum; then heat it strongly in an iron dish until no further change occurs. Results?

When the ignited alum is cold, taste it. Result? Place it in 5 c.c. water in a test tube, and boil carefully for five minutes. When the water is cool, taste it. Result?

Assuming that heat simply drove off crystal-water from the alum, upon what does the taste of crystalline alum seem to depend?

d. Heat a crystal of copper sulphate (blue vitriol) strongly in an iron dish. Result? When the residue is cold, add a few drops of water to it. Result? Explain.

EXPERIMENT XVIII.

EFFLORESCENCE AND DELIQUESCENCE.

Apparatus. Evaporating dish, beaker, watch glass.

Materials. Hydrates of sodium carbonate (washing soda) and of sodium sulphate (Glauber's salt), solid potassium hydroxide, anhydrous calcium chloride.

a. Expose a bright crystal of washing soda to the air for at least twenty-four hours. Result?

b. Carefully weigh your evaporating dish, and then weigh into it accurately about 5 g. of bright crystals of Glauber's salt (hydrate of sodium sulphate). Leave the dish uncovered for at least twenty-four hours, and weigh dish and contents. Result? Continue weighing at intervals until there is no further loss. Calculate the per cent of loss. What is it that escapes? Record your results systematically, as in Experiment VI.

c. In a small beaker place a piece of potassium hydroxide, and leave it exposed to the air at least an hour. Result?