(Adapted from Leach, "Food Inspection and Analysis.")
Place about 2 gms. of flour in a dish with 1/2 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 (NH_{ 4})_{ 2}CO_{ 3} solution used?
Testing Baking Powders for Phosphoric Acid
Dissolve 1/2 gm. of baking powder in 5 cc. of H_{ 2}O and 3 cc. HNO_{ 3}. 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?
Dissolve 1/2 gm. of material in 10 cc. water; filter off any insoluble residue and to the filtrate add 2 or 3 cc. NaOH and apply heat. Test the gas given off with moistened turmeric paper. If NH_{ 3} is present, the paper will be colored brown. Do not allow the paper to come in contact with the liquid or sides of the test tube. (Perform the tests on two samples of baking powder.)
1. How do you test a baking powder for ammonia? 2. Why do you add NaOH? 3. Why must you be careful not to let the turmeric paper touch the sides of the test tube or the liquid?
Into a weighed aluminum or porcelain dish pour 10 cc. of vinegar. Weigh and then evaporate over boiling water. To drive off the last traces of moisture dry in the water oven for an hour. Cool and weigh. Calculate the per cent of solids. Observe the appearance of the solids. Test both samples and compare.
1. How may the per cent of solids in vinegar be determined? 2. Describe the appearance of the solids from the good and from the poor sample of vinegar. 3. What is the legal standard for vinegar solids in your state?
Pour 170 cc. vinegar into 200 cc. cylinder. Place a hydrometer for heavy liquids (sp. gr. 1 to 1.1) in the cylinder. Note the depth to which it sinks and the point registered on the scale on the stem. Note temperature of vinegar. Record specific gravity of vinegar.