ze
(cubic contents), color, porosity, odor, taste, nature of crust, and
form of loaf.

Experiment No. 30

Microscopic Examination of Yeast

On a watch glass mix thoroughly a very small piece of yeast with about
5 cc. of water and then with the stirring rod place a drop of this
solution on the microscopical slide, adding a drop of very dilute methyl
violet solution. Cover with the cover glass and examine under the
microscope. The living active cells appear colorless while the decayed
and lifeless ones are stained. Yeast cells are circular or oval in
shape. (See Fig. 46.)

(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 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?

Experiment No. 32

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?

Experiment No. 33

Testing Baking Powders for Ammonia

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?

Experiment No. 34

Vinegar Solids

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
th