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.
The boiling point of water is called 212° F. but actually that temperature is reached only at sea level. For every 500 feet ascent the boiling point drops one degree. As altitudes rise in this country from sea level to 12,000 feet, food boils at 202° F. in Denver, and 198° F. in Laramie.
Simple boiling processes are carried on by the use of a pressure cooker or a sealed steamer as indicated under vegetable cookery (pages 386 to 388). In the baking of meats and vegetables oven heat can be regulated without regard to altitude. Above 7,000 feet, additional time must be allowed. The little book called "Vegetable Cookery at High Altitudes" by Emma J. Thicssen of the University of Wyoming will be found valuable.
Candy and frostings can no longer be tested by temperature because the soft-ball stage, which is 236° F. up to 1,000 feet, is 226° F. at 3,000 feet, 223° F. at 5,000 feet, and 220° F. at 7,000 feet. The other stages also occur at lower temperatures as the altitude rises. Testing consistency of the sirup by the finger or the saccharometer is the way out.
Marjorie W. Peterson of Colorado State College has made a careful study entitled "Baking Quick Breads and Cakes at High Altitudes," giving recipes for sea level with their necessary variations for 3,000 to 11,180 feet. Miss Peterson calls attention to some general requirements for all high levels. Cake and bread flours should be used exactly as indicated and not interchanged. Reductions in the amounts of sugar and baking powder as well as fat must also be made as the altitude rises, and while these bear a certain ratio per thousand feet, they are not regular. The modern woman living in high altitudes would do well to buy Miss Peterson's booklet.