EXPERIMENT 38: THE SOLUBILITY OF ALBUMIN.—Put a small portion of the broken egg white in a test tube. Half fill the tube with cold water. Then turn the contents of the tube on to a folded filter paper, and catch the filtrate in another test tube. Are the contents of the tube clear?
Apply heat to the filtrate. What happens? Does this prove that egg albumin was dissolved in the water before applying heat to the contents of the tube? Explain.
EXPERIMENT 39: TEMPERATURE AT WHICH EGGS COAGULATE.—Place a teaspoonful of white of egg in a test tube. Insert a thermometer in the test tube and place the test tube in a beaker of water (see Figure 39). Heat the water gradually. Note and record: (a) Temperature at which coagulation first appears. (b) Temperature at which the egg white is entirely coagulated. Has the water reached the boiling point when the egg white has entirely coagulated? What application can you draw from this as to the temperature of the water in which eggs may be cooked?
EXPERIMENT 40: COMPARISON OF COOKED AND BOILED EGGS.—Remove at once about half of the coagulated egg from the test tube of Experiment 39. Examine it and press it between the fingers.
Continue to heat the remainder of the egg in the test tube, allowing the water to boil a few minutes. Then remove the egg, examine it, and press it between the fingers. Compare it with the egg cooked below the boiling point of water. Which is more tender? Which breaks more easily? Which do you consider more palatable? What conclusion can you draw concerning the temperature at which eggs should be cooked to make them most tender and palatable?
DIGESTIBILITY AND PALATABILITY OF EGGS.—The experiments of this lesson show that eggs cooked at simmering temperature are more tender than those cooked at boiling temperature. The question may arise, is the tender egg more wholesome than the tough egg? It is true that eggs cooked below the boiling temperature will digest in a little less time than those cooked in boiling water. Since, however, the tougher egg is as completely digested as the more tender, the difference in the time of digestion is a matter of little importance.
[Illustration: FIGURE 39.—APPARATUS TO DETERMINE THE TEMPERATURE AT WHICH
EGGS COAGULATE.]
But even though the difference in digestion is not considered, the difference in palatability is worth some attention. If soft-cooked and soft-boiled eggs are compared, the soft-cooked will be found to be much more uniformly cooked. The white of a soft-boiled egg may be firm, while its yolk is very soft or the white may be soft while its yolk is raw.
STRUCTURE OF EGGS.—A hen's egg consists of shell, membrane, white, yolk, and the little mass in the yolk called the embryo, from which the young chicken grows. The yolk is kept in place by two twisted cords of white membrane. This membrane is the first part to disappear when the egg begins to spoil.
CARE AND USE OF EGGS.—(a) Wash eggs just before using. [Footnote 45: Washing removes a coating on egg-shells. This coating prevents the entrance of microorganisms. Hence eggs should not be washed until they are to be used.] The shells may be used for clearing coffee.