STRONTIUM AND BARIUM.

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b. To a piece of old mortar in a test tube add dilute hydrochloric acid. Identify the gas. What does fresh mortar absorb from the air?

c. Stir 10 c.c. plaster of Paris in an evaporating dish with enough water to form a fairly thick paste. Put the paste upon a piece of paper, and push into it a coin slightly coated with vaseline. At once wash the evaporating dish. Let the paste and coin stand an hour or more. Carefully remove the coin from the plaster. Result? d. To a solution containing a calcium salt, i. e., calcium ions, add ammonium carbonate solution. Result? See Experiment LIX, d.

e. Clean a platinum wire as in Experiment LIX, e, and determine what color calcium chloride gives to the flame. Repeat with calcium sulphate. Be sure to have concentrated hydrochloric acid upon the wire.

EXPERIMENT LXIII.

STRONTIUM AND BARIUM.

Apparatus. Platinum wire and test tubes.

Materials.

Strontium chloride and nitrate, barium chloride and nitrate; solutions of strontium and barium chlorides; ammonium carbonate solution; dilute sulphuric acid.

a. Treat 2 c.c. strontium chloride solution with a few drops of ammonium carbonate solution. Result? Repeat, using barium chloride in place of strontium chloride. Write equations.

b. Treat 2 c.c. strontium chloride solution with dilute

sulphuric acid. Result? See Experiment XLIV, a. Equation?

c. Clean the platinum wire as in Experiment LIX, e, and heat a bit of strontium chloride in the flame. Repeat with strontium nitrate, Sr(NO3)2. Results?

d. Repeat c, using the corresponding barium salts. Results? How distinguish between calcium, strontium, and barium salts?

EXPERIMENT LXIV.

MAGNESIUM.

Apparatus. - Tongs, test tubes.

Materials. Magnesium wire, dilute hydrochloric acid, solutions of magnesium sulphate and chloride, disodium hydrogen phosphate, and ammonium chloride and hydroxide, magnesite.

a. Hold a piece of magnesium wire 2 cm. long in the flame (use tongs). Result? Describe the product.

b. Treat a second piece of magnesium with dilute hydrochloric acid. Result? Identify the gas, and write the equation. See Experiment X.

c. To 2 c.c. of magnesium sulphate solution add sodium. carbonate solution. Result? Repeat, using magnesium chloride instead of the sulphate.

d. See Experiment LIV, d, for the action of a solution containing a magnesium salt with disodium hydrogen phosphate and ammonium hydroxide. Rewrite the equations here.

Repeat that experiment with magnesium chloride solution instead of the sulphate. Equation?

e. Treat a small piece (half a c.c.) of magnesite with dilute nitric acid. Result? Identify the gas, and write the equation.

From Experiment XLVIII, b, tell the effect of heat upon magnesite.

EXPERIMENT LXV.

ZINC.

Apparatus. File or sand-paper, knife, iron dish with flat bottom, test tubes, mouth blowpipe.

Materials. - Zinc, tin, lead, and copper; zinc dust; solutions of zinc sulphate, sodium hydroxide, and ammonium sulphide; dilute sulphuric and hydrochloric acids; hydrogen sulphide; stick of charcoal.

a. Clean part of a piece of zinc with a file or with sand-paper. Color? Is zinc hard or soft (use a knife or rough edge of glass)? Place a burner below the center of an iron dish. At equal distances from the center place pieces of zinc, tin, lead, and copper, and determine the order in which they melt. Return the metals to the proper bottles.

b. Heat a piece of zinc on charcoal with the oxidizing flame and with the reducing flame produced by the mouth. blowpipe. Results? To do this proceed as follows:

Hollow out a depression near one end of the charcoal, and into it put the zinc. To make the blowpipe flame, have a luminous Bunsen flame 4 cm. high, and hold the blowpipe so that the flame produced will be inclined about 30 degrees to the horizontal plane.

To make an oxidizing flame, hold the end of the blowpipe inside the luminous flame, a centimeter above the tip of the dark, inner cone. Hold the charcoal at such a distance that the zinc is in the outer, faintly-luminous part of the blowpipe flame.

To make a reducing flame, hold the tip of the blowpipe just at the outer edge of the flame at its middle part, and hold the assay (here, zinc) much nearer the blowpipe than in the oxidizing flame. The proper region is just at the tip of the inner, light-blue cone of the blowpipe flame.

c. What action has hydrochloric acid upon zinc? Equation? See Experiment VIII for the action of dilute sulphuric acid, and Experiment XVII for the behavior of zinc sulphate crystals, ZnSO4. 7 H2O, when heated.

d. Mix 1 c.c. zinc dust with 5 c.c. sodium hydroxide solution, and heat carefully. Test evolved gas with a flame. Result? The solution contains sodium zincate, Na2ZnO2. Write the equation.

e. To 2 c.c. zinc sulphate solution add a drop of sodium hydroxide solution. Result? What, probably, is the precipitate? Equation? Repeat with a second test tube. Now add to the first tube dilute hydrochloric acid, shaking. To the second tube add an excess of sodium hydroxide, shaking. Results? The alkaline solution contains sodium zincate. Equations?

What do these experiments show as to the nature of zinc hydroxide?

f. To 10 c.c. zinc sulphate solution add a drop of dilute sulphuric acid, and then hydrogen sulphide. Result? Put the solution into a beaker and add 5 c.c. ammonium sulphide solution, stirring. Result? The product is zinc sulphide, ZnS. Color? Equation?

EQUIVALENT OF ZINC.

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Add 10 c.c. water, stir the mixture, let it settle, and then pour off the supernatant liquid. Add 15 c.c. more water, stir, let settle, and decant, i. e., pour off the water. This is called "washing by decantation."

To the zinc sulphide add dilute sulphuric acid. Result? What is the gas? Equation? Why was not zinc sulphide precipitated by hydrogen sulphide?

EXPERIMENT LXVI.

EQUIVALENT OF ZINC.

Same as in Experiment X.

Zinc, in sheet form or in sticks; dilute (5%) sul

a. Dissolve zinc in dilute sulphuric acid just as you did magnesium in Experiment X, and find the volume of hydrogen liberated by a known weight of zinc. Use from 0.45 gram to 0.55 gram of zinc. If the zinc is in sheet form, it will react readily; but a little impurity, chiefly carbon, will remain insoluble. If the zinc is pure, it will react with difficulty; therefore wind about the zinc a piece of platinum wire or a narrow strip of platinum foil. Set the apparatus aside until the zinc is in solution; then proceed as in Experiment X.

b. Reduce the volume of hydrogen to standard conditions, and calculate the weight of the hydrogen obtained. Finally, solve for x in the proportion,

Wt. of zinc taken : Wt. of hydrogen obtained :: x: 1.

The value of x will be the equivalent of zinc.