Old recipes call for separating egg whites from yolks much more frequently than modern recipes. For example, a few days ago I needed to separate four eggs to make the hundred-year-old Lemon Meringue Pie recipe that I recently posted. The yolks went into the lemon custard filling and the whites into the meringue.
Old cake recipes also often call for separating the eggs and beating the whites before adding them to the batter to get a lighter, fluffier cake. . . and so do some old omelette recipes. . . . My list could so on and on.
Here are directions in a hundred-year-old home economics textbook for separating eggs:
Separating Whites from Yolks
Break the egg over a bowl, turn the small end down, and pull the shell apart, slipping the yolk from one half of the shell to the other once or twice, so that the white will drop into the bowl. If any of the yolk is mixed with the white, the white will not beat well on account of the fat present.
The Science of Home Making: A Textbook in Home Economics by Emma E. Pirie (1915)