domingo, 28 de dezembro de 2008

Gifted Cows

There are so many reasons to be thanking cows, clearly the milk is very good for you and they provide meat for those that are carnivorous, if you are enterprising and have space for cows, they can provide the methane for use as a fuel, they could pull your plough and cart and there product of milk can paint your house.
MILK PAINT is a very old invention and along with eggs has been a standard for fixing colours or as glue,
CASEIN. Chemistry: Casein Glue
Purpose: In this activity, you will separate a mixture and synthesize glue.
Background: Homogenized cow’s milk contains 4.4% fat, 3.8% protein, and 4.9% sugar. It has been well-mixed to prevent it from separating. At the normal pH of milk (about 6.3 – 6.6), the protein, called casein, remains evenly dispersed in the solution. When an acid is added to the mixture, the pH drops and the casein can no longer stay dissolved; it coagulates into an insoluble mass. This coagulation of casein occurs at a pH of about 4.6.
(casein) (lactose)
We will use skim milk in this activity, since it is easier to work with.
1. Pour about 100 mL of skim milk into a 400 mL beaker. Add 15 mL of white vinegar (5% acetic acid).
2. Place the mixture on a hot plate and heat, stirring gently with a glass stirring rod. Observe the mixture carefully and stop when you see turbidity (solid curds floating in the beaker). Do not overheat the mixture; the protein will denature and your glue won’t work.
3. Filter the mixture, using a folded piece of paper towel, into an Erlenmeyer flask. The curds should remain in the paper towel, while the filtrate (i.e., the liquid) will filter through into the flask. Discard the liquid filtrate; this contains the whey.
4. Scrape the curds from the paper towel into a small plastic cup.
5. Add ½ teaspoon of baking soda (NaHCO3) to the cup and stir with a wooden splint. Slowly add drops of water, stirring periodically, until the consistency of white glue is obtained.
6. Use your glue to make a collage. Put your name on your collage and set it aside to dry overnight.
Milk paint was made from old curdled milk or cottage cheese, lime and earth pigment for colour.
1870 Milk Paint Formula
* 1 Quart skim milk (room temperature)
* 1 Once of hydrated lime by weight (Available at building centres. Do not use quick lime, as it will react with the water and heat up. Hydrated lime has been soaked in water then dried.)
* 1 to 2 1/2 pounds of chalk may also be added as a filler.
Stir in enough skim milk to hydrated lime to make a cream. Add balance of skim milk. Now add sufficient amount of powder pigment to desired colour and consistency (Pigment powder must be lime proof ). Stir in well for a few minutes before using. For best results continue to stir throughout use.
Apply milk paint with a cheap natural bristle brush. Allow project to dry sufficiently before applying next coat.
Extra paint may be kept for several days in the refrigerator, until the milk sours.
Double or triple the recipe for paint. Allow to dry thoroughly 3-4 hours before use. For extra protection, give paint a coat of oil finish or sealer. Colour may change - test in inconspicuous area

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