Composition And Properties

Water is a compound of hydrogen and oxygen, consisting of two parts by volume of oxygen to one of hydrogen. Absolutely pure water is colorless, odorless, and tasteless, but such water is not found in nature, owing to its great solvent power, which causes it to dissolve substances with which it comes in contact. Water ordinarily, therefore, contains varying quantities of mineral and organic matter, including gases. To these substances in solution the characteristic flavor is due. Water from which the air has been expelled by long standing in a warm place, or by boiling, has a "flat " taste.

Water freezes at 32° F. On heating, the ice melts, and we may have ice water with a temperature of 32° F. When this water is warmed, the air dissolved in it begins to expand, and tiny bubbles appear, forming first on the sides of the vessel, and tending to rise to the surface. If the water there is not yet warmed, they contract and sink, but finally when the water is warm throughout, come to the surface and escape. After the air is thus expelled, if heating is continued, steam bubbles form in a similar manner. At 185° F., water bubbles below the surface, or simmers. When the bubbles reach the surface and break, giving off a cloud of steam, the boiling point has been reached, 212° F. Except under pressure, water can then become no hotter. Fast boiling simply means rapid evaporations and waste of fuel.

Source Of Water As Food

A considerable source of water is food itself. In green vegetables and fruits it constitutes as high as 85 per cent.-95 per cent. of the whole substance; in potatoes and other starchy vegetables it is present in as large amount as 75 per cent. Even in seemingly dry foods, as crackers, there may be as much as 5 to 10 per cent. But since 60 per cent. of the body itself is composed of water, and water loss through the lungs, skin, kidneys, etc., is very constant, the supply in ordinary diet is not sufficient, and water must be added as a beverage. This may be in the form of ordinary drinking water, of tea, coffee, or other similar beverages and of medicinal waters; the latter, however, should be considered chiefly under the head of drugs.

Functions Of Water In The Body

Water undergoes no chemical change in the body, yet the consideration of it is of vital importance. Solution is an essential part of digestion. Water bathes the tissues and washes away our waste and ex-crementitious matter. As it does not itself undergo any chemical alteration it is not susceptible of liberating force, consequently is not an energy-producing agent, but contributes to chemical changes by supplying a necessary condition for their occurrence.

Dr. Gilman Thompson summarizes the uses of water in the body as follows:

1. It enters into the chemical combination of the tissues.

2. It forms the chief ingredient of all the fluids of the body and maintains their proper degree of dilution.

3. By moistening various surfaces of the body, such as the mucous and serous membranes, it prevents friction and the uncomfortable symptoms which might result from their drying.

4. It furnishes in the blood and lymph a fluid medium by which food may be taken to remote parts of the body and the waste material removed, thus promoting rapid tissue changes.

5. It serves as a distributor of body heat.

6. It regulates the body temperature by the physical processes of absorption and evaporation.

Professional fasters have shown that one may live for weeks without food, but it may readily be demonstrated that a warm-blooded animal except in a state of hibernation or trance can subsist but a few days without water.

Food Uses Of Water

Water taken in considerable quantities with meals favors upward metabolism and increases the utilization of food. Thirst at meals does not always mean a true body demand for water, as it may be due to condiments, or to improper mastication of food. Under ordinary circumstances, about three or four pints daily are necessary to make up loss of water that is constantly being eliminated through the skin, kidneys, lungs and intestines. The quantity excreted daily varies greatly under special conditions. The demand for water is much increased by hot weather, and violent exercise, and diminished in the bedridden and sedentary. Babies, delirious patients, etc., should be fed water, as carefully as other food.