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city for washing, and then to determine the cost of the soap lost in one year owing to the use of hard water.

b. The analysis of washing-powders. Devise methods for detecting the presence of the following substances if present in washing-powders: (1) sodium carbonate; (2) borax (b, Exercise 62); (3) mineral matter, such as sand. Test one or more washing-powders for these substances.

EXERCISE 74

THE PREPARATION AND PROPERTIES OF
BLEACHING-POWDER

Apparatus. Flask (250-cc.) and two bottles (250-cc.) connected with glass tubing as shown in Fig. 48; 200-cc. beaker; stirring-rod.

Materials. 15 g. manganese dioxide; hydrochloric acid; 25 cc. of water in bottle B; 10 cc. of sodium hydroxide solution added to 50 cc. of water in D; sufficient calcium hydroxide (slaked lime) to half fill the tube C; strips of colored calico; sulfuric acid.

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(Hood.) Generate chlorine in A (Fig. 48). The gas must be evolved slowly, for which reason only a very gentle heat is applied to the flask. The gas bubbles through the water in B, then passes over the calcium hydroxide in C, any unabsorbed gas being caught in D (?).

When all of the chlorine has passed over from A, disconnect the apparatus and transfer the contents of the tube C to a beaker and pour over it 75 cc. of water containing 1 cc. of sulfuric acid. Stir well and immerse in the mixture some strips of colored calico for a few minutes (?). Complete the following equations:

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Apparatus. Porcelain crucible and cover; ring stand and burner; pipe-stem triangle; evaporating-dish; 2 test tubes.

Materials. Strips of magnesium 5 cm. long; small beaker; red litmus paper; 2 to 3 g. magnesium carbonate; magnesium sulfate solution (R. S.); ammonium chloride (R. S.); disodium phosphate (R. S.).

a. Wind a strip of magnesium wire into a coil and place it in a porcelain crucible. Put the cover on the crucible and apply a gentle heat. Raise the cover slightly from time to time so as to admit air. Continue until the magnesium is entirely burned, leaving a white powder. Cool, add water, and stir thoroughly; then test with litmus (?).

b. Convert 2 or 3 g. of magnesium carbonate into the chloride (R). Evaporate the solution to complete dryness in an evaporating-dish, heating the residue with the bare flame. When it is cool, add a few drops of water, stir, and test with litmus (?). Are waters containing magnesium chloride objectionable for use in steam boilers?

c. Pour 3 cc. of a solution of magnesium sulfate into a test tube and add an equal volume of a solution of ammonium chloride. Now add to this a few drops of a solution of disodium phosphate (Na2HPO). The precipitate has the composition MgNH PO, What is the name of this compound? To what class of compounds does it belong? The above reaction serves as a good test for magnesium compound.

EXERCISE 76

ZINC AND ITS COMPOUNDS

Apparatus. Blowpipe; burner; 3 test tubes; beaker.

Materials. 0.5 g. zinc; sulfuric acid; sodium hydroxide solution; ammonium sulfide (R.S.); 0.2 g. sodium carbonate dissolved in 3 cc. of water; 2 g. zinc sulfate; hydrochloric acid; pieces of charcoal.

a. Place a bit of zinc on charcoal and heat it in the tip of the flame of a blowpipe (R). The resulting compound is deposited as a film on the charcoal. Note the color of it. Is its color the same when hot as when cold?

b. Dissolve 0.5 g. of zinc sulfate in 20 cc. of water. Divide this solution into 3 parts and test with the following reagents: (1) sodium hydroxide solution (1 drop, or just sufficient to cause a precipitate); zinc hydroxide precipitates (R), but the precipitate dissolves again if an excess of sodium hydroxide is added; (2) ammonium sulfide (R) (note the color of the precipitate); zinc is the only metal which forms an insoluble white sulfide; (3) sodium carbonate solution; a basic carbonate is formed.

c. Devise a process for converting zinc sulfate into zinc chloride. Submit the process to your instructor for approval. When approved, prepare some of the chloride according to your process. For what is the compound used?

EXERCISE 77

ALUMINIUM AND ITS COMPOUNDS

Apparatus. 5 test tubes; blowpipe; burner; 2 beakers; piece of charcoal.

Materials. 1 g. aluminium; hydrochloric acid; ammonium hydroxide; sodium hydroxide; aluminium sulfate solution (R. S.); 2 or 3 drops of cobalt nitrate solution (R.S.); 1 g. sodium carbonate in 5 cc. of water; aluminium sulfate and potassium sulfate sufficient to make 20 g. of crystals of potassium alum.

a. Note the physical properties of aluminium. Add 5 cc. of water to a bit of the metal in a test tube and add hydrochloric acid, a drop at a time, sufficient to dissolve the metal. Filter (if necessary) and dilute the solution to about 10 cc. and divide it into two equal parts. To the first add ammonium hydroxide until the solution reacts alkaline (R); to the second add sodium hydroxide, a drop at a time, until a precipitate forms (R). Shake the latter tube and divide the mixture into two equal portions. To the one add hydrochloric acid, noting the result (R); to the other add sodium hydroxide solution until the precipitate dissolves (R). Is aluminium hydroxide an acid or a base?

b. Prepare some aluminium hydroxide by adding ammonium hydroxide to a solution of aluminium sulfate, and heat it on charcoal in the blowpipe flame (R). Moisten the residue with a drop or two of a solution of cobalt nitrate and reheat. Note the result. Advantage is taken of this property in detecting the presence of aluminium.

c. Add a solution of sodium carbonate to a solution of any salt of aluminium. Note that a gas is evolved (?). Devise a method for determining whether or not this gas is carbon dioxide, and make the test.

d. Calculate the weights of aluminium sulfate (the crystals of aluminium sulfate have the formula Al(SO), 18 H2O)

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and of potassium sulfate required to prepare 20 g. of crystals of potassium alum; then dissolve these amounts of the two compounds separately in as little water as possible, mix the two solutions thoroughly, and set aside for a few days to crystallize. If a string is suspended in the liquid, the crystals will deposit on it. These may then be withdrawn and their properties studied (?).

EXERCISE 78

THE USE OF ALUMINIUM SULFATE IN THE PURIFIICATION OF WATER

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Apparatus. Three 250-cc. wide-mouthed bottles; graduated tube. Materials. Aluminium sulfate solution (R. S.); limewater (R.S.). Label the three bottles A, B, and C respectively. Nearly fill A and B with muddy water, pouring a like volume of distilled water into C. Add 5 drops of aluminium sulfate solution to A and C respectively. Mix the contents of each bottle thoroughly. Now to bottles A and C (each) add 10 cc. of limewater. Set the bottles aside and examine at the beginning of the next laboratory period (?). "

For experiments on the use of aluminium compounds as mordants in dyeing, see Exercise 99, Appendix A.

EXERCISE 79

REACTIONS OF BAKING-POWDERS

Apparatus. Large test tube, and cork to fit; stirring-rod. Materials. 4 g. sodium bicarbonate; limewater (R.S.); alum; cream of tartar.

a. Grind together 2 g. of sodium bicarbonate and sufficient (?) alum to react with the bicarbonate. Put the mixture into a large test tube and cover the mixture with water. Cork the tube tightly and shake the mixture. Dip a glass

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