This section is from the book "The American Woman's Cook Book", by Ruth Berolzheimer. Also available from Amazon: The Domestic Arts Edition of the American Woman's Cook Book.
When ready to use stock, loosen fat around the edges with the thin blade of a knife. Remove the cake of fat. If the stock is jellied, wipe off the remaining small pieces of fat and the edge of the bowl with a cloth wrung out in hot water. If the stock is very soft or liquid, pass small sheets of absorbent paper over the top of the stock.
When Stock Must Be Used Before Cooling, skim off all the fat possible. Most of the remainder of the fat may be removed in one of two ways. The first way is to pass over the top small sheets of absorbent paper or blotting-paper. The second way is to cool the soup as much as possible beforehand, then to wrap a piece of ice in a cloth and let it down into the stock. Move the ice around just below the surface so that the fat on the surface is suddenly chilled, and it will gather on the cloth around the ice. This must be done quickly to prevent unnecessary dilution of the stock.
For Clear Soups, take the stock from the top of the bowl, being careful to avoid any sediment which may have escaped through the sieve and settled to the bottom of the bowl. This sediment is valuable as a food and should be reserved for gravies or soups which are not necessarily clear. Clarify this stock if a translucent, sparkling soup is desired.
To Clarify Soup - Allow one egg-white and shell to one quart of stock. Crush the shell into small pieces and mix with the slightly beaten egg-white. Heat the stock just enough to liquefy it, if it is jellied. Thoroughly stir the egg-white and shell into the stock. Heat to the boiling-point, stirring constantly, then boil without stirring two to five minutes. Add a cup of cold water and set on back of stove to settle. Strain through two thicknesses of cheese-cloth. The purpose of egg in clarifying soup is the same as in coffee. The coagulated egg gathers around itself the particles of solid substance in the soup, which otherwise would be fine enough to pass through a strainer.