This section is from the book "Philadelphia Cook Book: A Manual Of Home Economies", by Sarah Tyson Heston Rorer. Also available from Amazon: Philadelphia Cook Book.
All green vegetables should be freshly gathered, washed well in cold water, and cooked in freshly-boiled water until tender, no longer. After water has boiled for a time it parts with its gases and becomes hard, and most vegetables are better cooked in soft water. It is a well-known fact that split peas, dried beans and lentils do not boil soft in hard water. The salts of lime, sulphate or gypsum coagulate the casein which these seeds contain. In some cases, however, the solvent power of pure, soft water is so great that it destroys the firmness, color and outside covering (skin) of the green vegetables, and allows their juices to pass out into the water. This is especially true of green peas and beans. In these cases, therefore, hard water is better than soft. A teaspoonful of common salt added to every gallon of water hardens it at once. A half-teaspoonful of bi-carbonate of soda to every gallon of water renders it soft. French books recommend the same quantity of carbonate of ammonia for the latter purpose.
Young, green vegetables should be cooked in boiling salted water. Onions, if boiled in pure, soft water, are almost tasteless, and all the after-salting cannot restore to them the sweet saline taste and the strong aroma which they possess when boiled in hard water (salted).
If green vegetables are wilted, soak them for an hour or two in clear, cold water; never add salt, as it hardens the tissues.
Peas, beans and lentils are the most nutritious of all vegetable substances. They are said to contain as much carbon (heat-giving food) as wheat, and almost double the amount of nitrogen (muscle-forming food). The nitrogenous element of these vegetables consists chiefly of vegetable casein.
Lentils afford the most concentrated form of vegetable diet, and in olden times their nutritious value was fully appreciated. Esau sold his birthright for a mess of red lentil pottage. We read that the Pyramids were built by men who lived on lentils, garlic and water. A dish served to persons of distinction in the time of Pharaoh was composed of lentils, and with this high reputation they are almost unknown in this country, except to the Germans, who use them for soup, which, though made entirely without meat, is most nutritious.
The potato, next to wheat, is the most important food derived from the vegetable kingdom. We may class it among the starch vegetables. It contains but little muscle-forming food, and therefore should be eaten with lean meats or other nitrogenous food, supplying the elements wanting in that food, and correcting the influence of a too-concentrated form of nutriment. Potatoes are three-fourths water; the remaining one-fourth contains a large proportion of starch, with a small quantity of albumen, casein and gluten, dissolved in its juices.
In the spring the sprouts begin to grow at the expense of the starch in the potato; therefore, at this season they are less mealy and nutritious. The sprouts should be rubbed off as soon as they appear, or they will exhaust the starch. When they are wilted in this way they are improved by being soaked in cold water several hours before cooking, and put on to boil in cold water.
The cooking of potatoes is indeed an art; they are dressed in some way in almost every family every day, and no vegetable is so often poorly served. Observe the following rules and you will have no trouble:
1. Be careful in the choice of your potatoes; choose those of medium size, free from blemishes and of a yellowish-white color; and, if possible, acquaint yourself with the soil in which they were raised - those from a rich, heavy soil being more nutritious.
2. As the nutritious part of the potato lies near the skin, if you pare at all, do it very sparingly. As it contains potash, a constituent part of the blood, which is soluble in water, we would advise boiling in the jacket.
3. If your potatoes are not wilted, put them on to boil with just boiling water enough to cover them, place over a moderate fire to boil slowly until nearly done, then throw in a half-cup of cold water, which will chill the surface; by this you render the potato mealy throughout. Cook until soft enough to admit a fork.
4. When done, drain off every drop of water, uncover the saucepan, sprinkle the potatoes with salt, to absorb the moisture, and stand on the back part of the stove to dry, shaking them over, now and then, to expose every side of the potato to the air. Remove the skins quickly.
5. Serve in an uncovered dish.
Potatoes are more wholesome baked than boiled.