Since every man, woman, and child constantly breathes forth carbon dioxide, the danger in overcrowded rooms is great, and proper ventilation is of vital importance.

47. Ventilation. In estimating the quant.i.ty of air necessary to keep a room well aired, we must take into account the number of lights (electric lights do not count) to be used, and the number of people to occupy the room. The average house should provide at the _minimum_ 600 cubic feet of s.p.a.ce for each person, and in addition, arrangements for allowing at least 300 cubic feet of fresh air per person to enter every hour.

In houses which have not a ventilating system, the air should be kept fresh by intelligent action in the opening of doors and windows; and since relatively few houses are equipped with a satisfactory system, the following suggestions relative to intelligent ventilation are offered.

1. Avoid drafts in ventilation.

2. Ventilate on the sheltered side of the house. If the wind is blowing from the north, open south windows.

48. What Becomes of the Carbon Dioxide. When we reflect that carbon dioxide is constantly being supplied to the atmosphere and that it is injurious to health, the question naturally arises as to how the air remains free enough of the gas to support life. This is largely because carbon dioxide is an essential food of plants. Through their leaves plants absorb it from the atmosphere, and by a wonderful process break it up into its component parts, oxygen and carbon. They reject the oxygen, which pa.s.ses back to the air, but they retain the carbon, which becomes a part of the plant structure. Plants thus serve to keep the atmosphere free from an excess of carbon dioxide and, in addition, furnish oxygen to the atmosphere.

[Ill.u.s.tration: FIG. 24.--Making carbon dioxide from marble and hydrochloric acid.]

49. How to Obtain Carbon Dioxide. There are several ways in which carbon dioxide can be produced commercially, but for laboratory use the simplest is to mix in a test tube powdered marble, or chalk, and hydrochloric acid, and to collect the effervescing gas as shown in Figure 24. The substance which remains in the test tube after the gas has pa.s.sed off is a solution of a salt and water. From a mixture of hydrochloric acid (HCl) and marble are obtained a salt, water, and carbon dioxide, the desired gas.

50. A Commercial Use of Carbon Dioxide. If a lighted splinter is thrust into a test tube containing carbon dioxide, it is promptly extinguished, because carbon dioxide cannot support combustion; if a stream of carbon dioxide and water falls upon a fire, it acts like a blanket, covering the flames and extinguishing them. The value of a fire extinguisher depends upon the amount of carbon dioxide and water which it can furnish. A fire extinguisher is a metal case containing a solution of bicarbonate of soda, and a gla.s.s vessel full of strong sulphuric acid. As long as the extinguisher is in an upright position, these substances are kept separate, but when the extinguisher is inverted, the acid escapes from the bottle, and mixes with the soda solution. The mingling liquids interact and liberate carbon dioxide.

A part of the gas thus liberated dissolves in the water of the soda solution and escapes from the tube with the outflowing liquid, while a portion remains undissolved and escapes as a stream of gas. The fire extinguisher is therefore the source of a liquid containing the fire-extinguishing substance and further the source of a stream of carbon dioxide gas.

[Ill.u.s.tration: FIG. 25.--Inside view of a fire extinguisher.]

51. Carbon. Although carbon dioxide is very injurious to health, both of the substances of which it is composed are necessary to life.

We ourselves, our bones and flesh in particular, are partly carbon, and every animal, no matter how small or insignificant, contains some carbon; while the plants around us, the trees, the gra.s.s, the flowers, contain a by no means meager quant.i.ty of carbon.

Carbon plays an important and varied role in our life, and, in some one of its many forms, enters into the composition of most of the substances which are of service and value to man. The food we eat, the clothes we wear, the wood and coal we burn, the marble we employ in building, the indispensable soap, and the ornamental diamond, all contain carbon in some form.

52. Charcoal. One of the most valuable forms of carbon is charcoal; valuable not in the sense that it costs hundreds of dollars, but in the more vital sense, that its use adds to the cleanliness, comfort, and health of man.

The foul, bad-smelling gases which arise from sewers can be prevented from escaping and pa.s.sing to streets and buildings by placing charcoal filters at the sewer exits. Charcoal is porous and absorbs foul gases, and thus keeps the region surrounding sewers sweet and clean and free of odor. Good housekeepers drop small bits of charcoal into vases of flowers to prevent discoloration of the water and the odor of decaying stems.

If impure water filters through charcoal, it emerges pure, having left its impurities in the pores of the charcoal. Practically all household filters of drinking water are made of charcoal. But such a device may be a source of disease instead of a prevention of disease, unless the filter is regularly cleaned or renewed. This is because the pores soon become clogged with the impurities, and unless they are cleaned, the water which flows through the filter pa.s.ses through a bed of impurities and becomes contaminated rather than purified. Frequent cleansing or renewal of the filter removes this difficulty.

Commercially, charcoal is used on a large scale in the refining of sugars, sirups, and oils. Sugar, whether it comes from the maple tree, or the sugar cane, or the beet, is dark colored. It is whitened by pa.s.sage through filters of finely pulverized charcoal. Cider and vinegar are likewise cleared by pa.s.sage through charcoal.

The value of carbon, in the form of charcoal, as a purifier is very great, whether we consider it a deodorizer, as in the case of the sewage, or a decolorizer, as in the case of the refineries, or whether we consider the service it has rendered man in the elimination of danger from drinking water.

53. How Charcoal is Made. Charcoal may be made by heating wood in an oven to which air does not have free access. The absence of air prevents ordinary combustion, nevertheless the intense heat affects the wood and changes it into new substances, one of which is charcoal.

The wood which smolders on the hearth and in the stove is charcoal in the making. Formerly wood was piled in heaps, covered with sod or sand to prevent access of oxygen, and then was set fire to; the smoldering wood, cut off from an adequate supply of air, was slowly transformed into charcoal. Scattered over the country one still finds isolated charcoal kilns, crude earthen receptacles, in which wood thus deprived of air was allowed to smolder and form charcoal. To-day charcoal is made commercially by piling wood on steel cars and then pushing the cars into strong walled chambers. The chambers are closed to prevent access of air, and heated to a high temperature. The intense heat transforms the wood into charcoal in a few hours. A student can make in the laboratory sufficient charcoal for art lessons by heating in an earthen vessel wood buried in sand. The process will be slow, however, because the heat furnished by a Bunsen burner is not great, and the wood is transformed slowly.

A form of charcoal known as animal charcoal, or bone black, is obtained from the charred remains of animals rather than plants, and may be prepared by burning bones and animal refuse as in the case of the wood.

Destructive Distillation. When wood is burned without sufficient air, it is changed into soft brittle charcoal, which is very different from wood. It weighs only one fourth as much as the original wood. It is evident that much matter must leave the wood during the process of charcoal making. We can prove this by putting some dry shavings in a strong test tube fitted with a delivery tube. When the wood is heated a gas pa.s.ses off which we may collect and burn. Other substances also come off in gaseous form, but they condense in the water. Among these are wood alcohol, wood tar, and acetic acid. In the older method of charcoal making all these products were lost. Can you give any uses of these substances?

54. Matter and Energy. When wood is burned, a small pile of ashes is left, and we think of the bulk of the wood as destroyed. It is true we have less matter that is available for use or that is visible to sight, but, nevertheless, no matter has been destroyed. The matter of which the wood is composed has merely changed its character, some of it is in the condition of ashes, and some in the condition of invisible gases, such as carbon dioxide, but none of it has been destroyed. It is a principle of science that matter can neither be destroyed nor created; it can only be changed, or transformed, and it is our business to see that we do not heedlessly transform it into substances which are valueless to us and our descendants; as, for example, when our magnificent forests are recklessly wasted. The smoke, gases, and ashes left in the path of a raging forest fire are no compensation to us for the valuable timber destroyed. The sum total of matter has not been changed, but the amount of matter which man can use has been greatly lessened.

The principle just stated embodies one of the fundamental laws of science, called the law of the _conservation of matter_.

A similar law holds for energy as well. We can transform electric energy into the motion of trolley cars, or we can make use of the energy of streams to turn the wheels of our mills, but in all these cases we are transforming, not creating, energy.

When a ball is fired from a rifle, most of the energy of the gunpowder is utilized in motion, but some is dissipated in producing a flash and a report, and in heat. The energy of the gunpowder has been scattered, but the sum of the various forms of energy is equal to the energy originally stored away in the powder. The better the gun is, the less will be the energy dissipated in smoke and heat and noise.

CHAPTER V

FOOD

55. The Body as a Machine. Wholesome food and fresh air are necessary for a healthy body. Many housewives, through ignorance, supply to their hard-working husbands and their growing sons and daughters food which satisfies the appet.i.te, but which does not give to the body the elements needed for daily work and growth. Some foods, such as lettuce, cuc.u.mbers, and watermelons, make proper and satisfactory changes in diet, but are not strength giving. Other foods, like peas and beans, not only satisfy the appet.i.te, but supply to the body abundant nourishment. Many immigrants live cheaply and well with beans and bread as their main diet.

It is of vital importance that the relative value of different foods as heat producers be known definitely; and just as the yard measures length and the pound measures weight the calorie is used to measure the amount of heat which a food is capable of furnishing to the body.

Our bodies are human machines, and, like all other machines, require fuel for their maintenance. The fuel supplied to an engine is not all available for pulling the cars; a large portion of the fuel is lost in smoke, and another portion is wasted as ashes. So it is with the fuel that runs the body. The food we eat is not all available for nourishment, much of it being as useless to us as are smoke and ashes to an engine. The best foods are those which do the most for us with the least possible waste.

56. Fuel Value. By fuel value is meant the capacity foods have for yielding heat to the body. The fuel value of the foods we eat daily is so important a factor in life that physicians, diet.i.tians, nurses, and those having the care of inst.i.tutional cooking acquaint themselves with the relative fuel values of practically all of the important food substances. The life or death of a patient may be determined by the patient's diet, and the working and earning capacity of a father depends largely upon his prosaic three meals. An ounce of fat, whether it is the fat of meat or the fat of olive oil or the fat of any other food, produces in the body two and a quarter times as much heat as an ounce of starch. Of the vegetables, beans provide the greatest nourishment at the least cost, and to a large extent may be subst.i.tuted for meat. It is not uncommon to find an outdoor laborer consuming one pound of beans per day, and taking meat only on "high days and holidays."

[Ill.u.s.tration: FIG. 26.--The bomb calorimeter from which the fuel value of food can be estimated.]

The fuel value of a food is determined by means of the _bomb calorimeter_ (Fig. 26). The food substance is put into a chamber _A_ and ignited, and the heat of the burning substance raises the temperature of the water in the surrounding vessel. If 1000 grams of water are in the vessel, and the temperature of the water is raised 2 C., the number of calories produced by the substance would be 2000, and the fuel value would be 2000 calories.[A] From this the fuel value of one quart or one pound of the substance can be determined, and the food substance will be said to furnish the body with that number of heat units, providing all of the pound of food were properly digested.

[Footnote A: As applied to food, the calorie is greater than that used in the ordinary laboratory work, being the amount of heat necessary to raise the temperature of 1000 grams of water 1 C., rather than 1 gram 1 C.]

TABLE SHOWING THE NUMBER OF CALORIES FURNISHED BY ONE POUND OF VARIOUS FOODS ----------------------------------------------------

FOOD

CALORIES

FOOD

CALORIES

----------------------------------------------------

Leg of lean mutton

790

Carrots

210

----------------------------------------------------

Rib of beef

1150

Lettuce

90

----------------------------------------------------

Shad

380

Onion

225

----------------------------------------------------

Chicken

505

Cuc.u.mber

80

----------------------------------------------------

Apples

290

Almonds

3030

----------------------------------------------------

Bananas

460

Walnuts

3306

----------------------------------------------------

Prunes

370

Peanuts

2560

----------------------------------------------------

Watermelons

140

Oatmeal

4673

----------------------------------------------------

Lima beans

570

Rolled wheat

4175

----------------------------------------------------

Beets

215

Macaroni

1665

----------------------------------------------------

57. Varied Diet. The human body is a much more varied and complex machine than any ever devised by man; personal peculiarities, as well as fuel values, influence very largely the diet of an individual.

Strawberries are excluded from some diets because of a rash which is produced on the skin, pork is excluded from other diets for a like reason; cauliflower is absolutely indigestible to some and is readily digested by others. From practically every diet some foods must be excluded, no matter what the fuel value of the substance may be.

Then, too, there are more uses for food than the production of heat.

Teeth and bones and nails need a constant supply of mineral matter, and mineral matter is frequently found in greatest abundance in foods of low fuel value, such as lettuce, watercress, etc., though practically all foods yield at least a small mineral const.i.tuent. When fuel values alone are considered, fruits have a low value, but because of the flavor they impart to other foods, and because of the healthful influence they exercise in digestion, they cannot be excluded from the diet.

Care should be constantly exercised to provide substantial foods of high fuel value. But the nutritive foods should be wisely supplemented by such foods as fruits, whose real value is one of indirect rather then direct service.

58. Our Bodies. Somewhat as a house is composed of a group of bricks, or a sand heap of grains of sand, the human body is composed of small divisions called cells. Ordinarily we cannot see these cells because of their minuteness, but if we examine a piece of skin, or a hair of the head, or a tiny sliver of bone under the microscope, we see that each of these is composed of a group of different cells. A merchant, watchful about the fineness of the wool which he is purchasing, counts with his lens the number of threads to the inch; a physician, when he wishes, can, with the aid of the microscope, examine the cells in a muscle, or in a piece of fat, or in a nerve fiber. Not only is the human body composed of cells, but so also are the bodies of all animals from the tiny gnat which annoys us, and the fly which buzzes around us, to the mammoth creatures of the tropics.

These cells do the work of the body, the bone cells build up the skeleton, the nail cells form the finger and toe nails, the lung cells take care of breathing, the muscle cells control motion, and the brain cells are responsible for thought.

59. Why we eat so Much. The cells of the body are constantly, day by day, minute by minute, breaking down and needing repair, are constantly requiring replacement by new cells, and, in the case of the child, are continually increasing in number. The repair of an ordinary machine, an engine, for example, is made at the expense of money, but the repair and replacement of our human cell machinery are accomplished at the expense of food. More than one third of all the food we eat goes to maintain the body cells, and to keep them in good order. It is for this reason that we consume a large quant.i.ty of food.

If all the food we eat were utilized for energy, the housewife could cook less, and the housefather could save money on grocer's and butcher's bills. If you put a ton of coal in an engine, its available energy is used to run the engine, but if the engine were like the human body, one third of the ton would be used up by the engine in keeping walls, shafts, wheels, belts, etc., in order, and only two thirds would go towards running the engine. When an engine is not working, fuel is not consumed, but the body requires food for mere existence, regardless of whether it does active work or not. When we work, the cells break down more quickly, and the repair is greater than when we are at rest, and hence there is need of a larger amount of food; but whether we work or not, food is necessary.

60. The Different Foods. The body is very exacting in its demands, requiring certain definite foods for the formation and maintenance of its cells, and other foods, equally definite, but of different character, for heat; our diet therefore must contain foods of high fuel value, and likewise foods of cell-forming power.

Although the foods which we eat are of widely different character, such as fruits, vegetables, cereals, oils, meats, eggs, milk, cheese, etc., they can be put into three great cla.s.ses: the carbohydrates, the fats, and the proteids.

61. The Carbohydrates. Corn, wheat, rye, in fact all cereals and grains, potatoes, and most vegetables are rich in carbohydrates; as are also sugar, mola.s.ses, honey, and maple sirup. The foods of the first group are valuable because of the starch they contain; for example, corn starch, wheat starch, potato starch. The substances of the second group are valuable because of the sugar they contain; sugar contains the maximum amount of carbohydrate. In the sirups there is a considerable quant.i.ty of sugar, while in some fruits it is present in more or less dilute form. Sweet peaches, apples, grapes, contain a moderate amount of sugar; watermelons, pears, etc., contain less. Most of our carbohydrates are of plant origin, being found in vegetables, fruits, cereals, and sirups.

Carbohydrates, whether of the starch group or the sugar group, are composed chiefly of three elements: carbon, hydrogen, and oxygen; they are therefore combustible, and are great energy producers. On the other hand, they are worthless for cell growth and repair, and if we limited our diet to carbohydrates, we should be like a man who had fuel but no engine capable of using it.

62. The Fats. The best-known fats are b.u.t.ter, lard, olive oil, and the fats of meats, cheese, and chocolate. When we test fats for fuel values by means of a calorimeter (Fig. 26), we find that they yield twice as much heat as the carbohydrates, but that they burn out more quickly. Dwellers in cold climates must constantly eat large quant.i.ties of fatty foods if they are to keep their bodies warm and survive the extreme cold. Cod liver oil is an excellent food medicine, and if taken in winter serves to warm the body and to protect it against the rigors of cold weather. The average person avoids fatty foods in summer, knowing from experience that rich foods make him warm and uncomfortable. The harder we work and the colder the weather, the more food of that kind do we require; it is said that a lumberman doing heavy out-of-door work in cold climates needs three times as much food as a city clerk. Most of our fats, like lard and b.u.t.ter, are of animal origin; some of them, however, like olive oil, peanut b.u.t.ter, and coconut oil, are of plant origin.

[Ill.u.s.tration: FIG. 27.--_a_ is the amount of fat necessary to make one calorie; _b_ is the amount of sugar or proteid necessary to make one calorie.]