around it about 5 cm. from the closed end. Weigh accurately 2 g. of granulated zinc and place it in A. Through the funnel tube add 10 cc. of twice normal hydrochloric acid, to which 2 drops of cupric sulfate has been added (why?), and bring the end of the delivery tube B under C so as to collect the evolved hydrogen. At once note the exact time to the second. Keep the rubber band at the level of the water in the beaker, and when the hydrogen has displaced the water in C to this level, again read the time to the second. Repeat the entire experiment, substituting twice normal sulfuric acid for the hydrochloric acid. Again repeat, using twice normal B FIG. 31 acetic acid. Compare the time required in the three experiments. Which experiment requires the shortest time? Which the longest? What do you conclude as to the relative strengths of the three acids? c. Repeat the three experiments in b, using pieces of magnesite (MgCO) of equal size instead of the zinc. Gaseous carbon dioxide (CO) is evolved in this reaction. What is now the order of the three acids in strength? CHAPTER IX COMPOUNDS OF NITROGEN 72. Preparation of ammonia. a. Dissolve 1 g. of ammonium chloride in a little water in a test tube and heat to boiling. Can you detect the odor of ammonia? Add a few drops of a solution of sodium hydroxide. Is the ammonia liberated (R)? Moisten a small strip of red litmus paper and hold it at the mouth of the tube. Note the result. Hold the end of a glass rod moistened with concentrated hydrochloric acid in the mouth of the tube. What is formed (R)? b. Usual laboratory method. This differs from the method used in a only in the fact that the less expensive calcium hydroxide (slaked lime) is sub stituted for sodium hydroxide. Fig. 32 shows the form of apparatus used. A represents a 250-cc. flask; B and C are 250-cc. wide-mouthed bottles partly filled with water. Notice that the glass tubes extending into the bottles do not quite touch the surface of the water. Why? Two dry bottles will also be needed for collecting some of the gas. Put into the flask A an inti- · mate mixture of about 30 g. of finely powdered slaked lime B FIG. 32 E and 15 g. of ammonium chloride; place it on a sand bath and heat gently with a small flame. A wire gauze may be |