a. Fat Content of Milk by Means of Babcock Test.—Measure with pipette into test bottle 17.6 cc. of milk. Sample should be carefully taken and well mixed. Measure with cylinder 17.5 cc. commercial H2SO4 and add to milk in test bottle. (See Fig. 25.) Mix acid and milk by rotating the bottle. Then place test bottles in centrifugal machine and whirl 5 minutes. Add sufficient hot water to test bottles to bring contents up to about the 8th mark on stem. Then whirl bottles 2 minutes longer and read fat. Read from extreme lowest to highest point. Each large division as 1 to 2 represents a whole per cent, each small division 0.2 of a per cent.
b. Determining Specific Gravity by Means of Lactometer.—Pour 150 cc. of milk into 200 cc. cylinder. Place lactometer in milk and note depth to which it sinks as indicated on stem. Note also temperature of milk. For each 10° above 60° F. add 1 to the lactometer number, in order to make the necessary correction for temperature. For example, if milk has sp. gr. of 1.032 at temperature of 70°, it will be equivalent to sp. gr. of 1.033 at 60°. Ordinarily milk has a sp. gr. of 1.029 to 1.034. If milk has sp. gr. less than 1.029, or contains less than 3 per cent fat, it may be considered watered milk. If the milk has a high sp. gr. (above 1.035) and a low content of fat, some of the fat has been removed.
(For extended direction for milk testing see Snyder's "Dairy Chemistry.")
Experiment No. 21
Boric Acid in Meat
Cut into very small pieces 5 gms, of meat, removing all the fat possible. Place in an evaporating dish with 20 to 25 cc. of water to which a few drops of HCl have been added and warm slightly. Dip a piece of turmeric paper in the meat extract and dry. A rose-red color of the turmeric paper after drying (turned olive by a weak ammonia solution) is indicative of boric acid.
1. How may meat be tested for boric acid? 2. Why is HCl added to the water? 3. Why is the water containing the meat warmed slightly? 4. What is the appearance of the turmeric paper after being dipped in the meat extract and dried? 5. What change takes place when it is moistened with ammonia, and why?
Experiment No. 22
Microscopic Examination of Cereal Starch Grains
Make a microscopic examination and drawings of wheat, corn, rice, and oat starch grains, comparing them with the drawings of the different starch grains on the chart. If the material is coarse, pulverize in a mortar and filter through cloth. Place a drop or two of the starchy water on the slide, cover with a cover glass, and examine.