From Miss Parloa's New Cookbook, via Project Gutenberg.
The old method of boiling coffee is still practised by at least one-half the housekeepers in this country. The coffee is sometimes boiled with an egg, which makes it perfectly clear, and also enriches it. When an egg is not used a small piece of salt fish skin is boiled with the coffee to clear it.
Directions for making: A small cupful of roasted and ground coffee, one-third Mocha and two-thirds Java; a small egg, shell and all, broken into the pot with the dry coffee. Stir veil with a spoon, and then pour on three pints of boiling water. Let it boil from five to ten minutes, counting from the time it begins to boil. As soon as it has boiled enough, pour in a cupful of cold water, and turn a little of the coffee into a cup, to see that the nozzle of the pot is not filled with grounds. Turn this back, and let the coffee stand a few moments to settle, taking care that it does not boil again. The advantages of boiled coffee are that when the egg is used the yolk gives a very rich flavor, and when the milk or cream is added the coffee has a rich, yellow look, which is pleasing. It has also a peculiar flavor, which many people prefer to the flavor gained by any other process. The disadvantages are that the egg coats the dry coffee, and when the hot water is added the coating becomes hard, and a great deal of the best of the coffee remains in the grounds after boiling. Also, in boiling, much of the fine flavor is lost in the steam that escapes from the pot.