(Adapted from Leach, "Food Inspection and Analysis.")
Experiment No. 31
Testing Baking Powders for Alum
Place about 2 gms. of flour in a dish with ½ gm. baking powder. Add enough water to make a dough and then 2 or 3 drops of tincture of logwood and 2 or 3 drops of ammonium carbonate solution. Mix well and observe; a blue color indicates alum. Try the same test, using flour only for comparison.
1. How do you test a baking powder for alum? 2. What difference in color did you observe in the test with the baking powder containing alum and in that with the flour only? 3. Why is the (NH4)2CO3 solution used?
Experiment No. 32
Testing Baking Powders for Phosphoric Acid
Dissolve ½ gm. of baking powder in 5 cc. of H2O and 3 cc. HNO3. Filter and add 3 cc. ammonium molybdate. Heat gently. A yellow precipitate indicates phosphoric acid.
1. How do you test a baking powder for phosphoric acid? 2. What is the yellow precipitate obtained in this test?