I said "ten minutes or more," because, when thus cooked, a prolonged exposure to the hot water does no mischief; if the temperature of 160° is not exceeded, it may remain for half an hour; in fact, the perfection of cooking, according to my experience (I always cook my own eggs when I have the opportunity and can spare the time), is attained when kept at 160 about twenty minutes. The 180° is above named because the rising of the temperature of the egg itself is due to the difference between its own temperature and that of the water, and, when that difference is very small, this takes place very slowly, besides which the temperature of the water is, of course, lowered in raising that of the cold egg.
In order to test this principle severely, I have just made the following experiment: At 10.30 p. m. I placed a new-laid egg in a covered stone-ware jar, of about one pint capacity, and filled this with boiling water; then wrapped the jar in many folds of flannel—so many that, with the egg, they filled a hat-case in which I placed the bundle—and left it there until breakfast-time next morning, ten hours later.
On unrolling, I found the water cooled down to 95°, that the yolk of the egg was hard, but the white only just solidified and much softer than the yolk. On repeating the experiment, and leaving the egg in its flannel coating for four hours, the temperature of the water was 123, and the egg in similar condition—the white cooked in perfection, delicately tender, but the yolk too hard. A third experiment of twelve hours, water at 200—on starting, gave similar result as regards the state of the egg.
This brings out a fact hitherto unknown to either cooks or chemists, viz., that the yolk coagulates firmly at a lower temperature than the white. Whether this is due to a different condition of the albumen itself or the action of the other constituents on the albumen, requires further research to determine.
When eggs are cooked in the ordinary way, the three and a half minutes' immersion is insufficient to allow the heat to pass fully to the middle of the egg, and therefore the white is subjected to a higher temperature than the yolk. In my experiment there was time for a practically uniform diffusion of the heat throughout.
I shall describe hereafter what is called the "Norwegian" cooking apparatus, wherein fowls, etc., are cooked as the eggs were in my hat-case.
Albumen exists in flesh as one of its juices, rather than in a definitely organized condition. It is distributed between the fibers of the lean (i. e., the muscles), and it lubricates the tissues generally, besides being an important constituent of the blood itself—of that portion of the blood which remains liquid when the blood is dead, i. e., the serum. As blood is not an ordinary article of food, excepting in the form of "black-puddings," its albumen need not be here considered, nor the debated question of whether its albumen is identical with the albumen of the flesh.
