Water forms more than two thirds of the whole body. It is especially abundant in the blood and secretions. It gives them the necessary fluidity, and enables them to dissolve the important materials they contain. It is contained in all kinds of solid food, as well as in the liquids drunk as beverages. It is most abundant in fruits and vegetables. Every pound of perfectly dry food should be accompanied with four pounds of water.
Pure water is composed of oxygen and hydrogen, one ninth hydrogen and eight ninths oxygen by weight. The usual test for pure drinking water is that it be "free from color, smell, or taste, be soft, bright, and aerated, and free from all deposit."
But it is very seldom found in that condition, as its power of dissolving other substances is so great that it nearly always holds animal, vegetable, or mineral matters in solution, obtained from the earth through which it flows. It also absorbs gases and odors from the air. The animal and vegetable substances found in it render it impure. But the mineral matters, unless in excess, are not objectionable.
When water contains more than a few grains to the gallon of carbonate of lime, it is termed hard water. When water is hard or impure, it should be boiled before being used for drinking, as this destroys the vegetable and animal impurities.
Water evaporates at all temperatures, boils at 212°, and freezes at 32° Fahrenheit. In freezing, the substances dissolved in water are expelled. Water, as it approaches the freezing-point, expands, and often bursts the vessels in which it is contained. In ponds or rivers it expands, becomes lighter, freezes, and floats on the surface in the form of ice.
Water is perfectly neutral. It combines with acids and with bases. It becomes sweet, sour, salt, astringent, bitter, or poison-ous, according to the nature of the bodies it holds in solution.
The chief purpose of mineral ingredients is to replenish certain tissues, and aid in the transference and absorption of the combustible nutrients, as a scaffolding aids in the construction of a building.
Chloride of sodium, or common salt, is essential to the life of the higher animals. It exists in all parts of the body. It is more abundant in the blood than any other inorganic ingredient except water; but it is an active poisonous irritant if taken in excess, causing diseases of the mucous membranes, as in catarrh, and stiffening of the muscles, as in rheumatism. We take it as a natural ingredient in many kinds of food, and as a condiment to increase the relish of many others.
The desire for salt is instinctive. There are people who do not use salt in food, but it is probable that they obtain sufficient sodium and chlorine in the brackish water they drink; or it may be, their habits of life render less salt necessary.
Salt taken with our food supplies two substances. Its chlorine supplies the hydrochloric acid of the gastric juice, that helps digest our food; and soda, which is an element of the bile, -a fluid which must be added to the dissolved or softened food before the nourishment can be extracted from it. People would very soon become ill if deprived of salt. A person requires from one fourth to half an ounce of salt daily. The attractive flavor which is developed by cooking and adding salt to our food excites the secretion of saliva and gastric juice, and therefore helps digestion. The Dutch used to condemn criminals to a diet of unsalted food. They suffered great physical torture, which soon ended in death.
Salt is one of the most abundant of all minerals. It is obtained from springs by evaporation, and from natural mines. It is readily soluble in hot or cold water. It is used for packing and preserving meats, as it prevents putrefaction by absorbing water from the flesh.
The other mineral ingredients needed in the system are combinations of lime, soda, potash, magnesia, sulphur, phosphorus, and iron. Phosphorus, lime, and magnesia are found in meat, fish, the cereals, and potatoes. Potash is found in meat, fish, milk, vegetables, and the dry seeds and fleshy parts of fruits, iron, in flesh, vegetables, and nearly all food, in very minute quantities..
Sulphur is in fibrine, albumen, and caseine. There is sufficient saline matter, except common salt, in all the ordinary food we eat and the water we drink.
These mineral matters become rearranged and combined before becoming part of the body, but they do not undergo any chemical change or decomposition. They are absorbed with the food, and form for a time part of the animal tissues, after which they are discharged with the secretions, and replaced by a fresh supply. They are absolutely indispensable to the nourishment of the body.