methods (R). How could you prepare from calcium carbonate the following compounds: calcium chloride, calcium sulfate, calcium nitrate, calcium oxide (R)? Why are carbonates so readily decomposed by acids?

h. Phosphates. Recall the formulas and the names of the three phosphoric acids, also the action of silver nitrate on their salts.

i. Orides. Burn a bit of magnesium wire 1 or 2 cm. in length (R). Heat a crystal of lead nitrate in a test tube (R). Heat a small piece of limestone on a wire gauze (R).

j. Hydrorides. Hold a piece of lime the size of a walnut in water for a few seconds, then place it on a watch glass and set it aside for a half hour. Note the change (R). Pour into separate test tubes about 1 cc. of a solution of each of the following compounds: ferric chloride (FeCl); magnesium sulfate (MgSO); copper sulfate (CuSO). Add to each solution 2 drops of a solution of sodium hydroxide (R). Now add a few drops of hydrochloric acid to each test tube, and explain the results.

165. Equilibrium. a. To 3 or 4 cc. of a solution of barium chloride add dilute sulfuric acid, drop by drop, as long as a precipitate is produced. Is the reaction a complete one? In a similar way, to a solution of calcium chloride add a solution of oxalic acid as long as calcium oxalate (CaCO) is precipitated. To test the completeness of the reaction, filter off the precipitate and add ammonium hydroxide to the filtrate until it is alkaline in reaction. Does an additional precipitate form? Can it be ammonium oxalate? What is it? Why did it not appear before the ammonium hydroxide was added? If ammonium oxalate is added in excess to calcium chloride, is the reaction complete? Why is it incomplete when the free acid is used?

b. Make a list of about a dozen acids which you have studied. What insoluble salts do they form? Prepare an insoluble salt of each (if it forms one) and try its solubility in hydrochloric acid. Which ones should be insoluble? Why? Do your experiments confirm your predictions?

CHAPTER XXVIII

THE ALKALI METALS

NOTE. Some preliminary experiments with sodium and sodium hydroxide have been given in Chapter XI. The student should review these carefully in connection with the present chapter.

166: Action of sodium hydroxide upon soluble salts of other metals. Try the effect of the solution of sodium hydroxide upon a soluble salt of each of the following: barium, potassium, magnesium, zinc, copper (R). In each case add a few drops at first, and if a precipitate forms, add an excess to see whether the precipitate redissolves. Make a list of the hydroxides soluble in water, and another list of those which redissolve in an excess of sodium hydroxide.

167. Preparation of sodium chloride. Dissolve 5 g. of sodium carbonate in 20 cc. of water. Prepare common salt from this (R). How can you be sure that the product contains no unchanged sodium carbonate? Describe the method (R). Treat some of the salt so prepared with sulfuric acid. What gas is evolved (R)?

168. Purification of common salt. The impurities most likely to be present are sulfates and chlorides of calcium and of magnesium. Dissolve about 25 g. of common salt in 100 or 150 cc. of water and heat to boiling. Add a solution of barium hydroxide, 1 cc. at a time, as long as you are sure that the precipitate is increasing (R). Without filtering, add a concentrated solution of sodium carbonate, drop by drop, as long as it produces a precipitate. If the solution becomes too turbid for you to be sure of this, filter it. What is precipitated (R)? When the precipitation is complete, filter. What impurity may now be present? Add dilute hydrochloric acid