Chapter V: Part I: Explanatory Lessons (1)

PREPARATION OF FOOD

=Digestibility.= There are comparatively few kinds of food that can be eaten uncooked. Various fruits, milk, oysters, eggs, and some other things may be eaten raw, but the great mass of food materials must be prepared by some method of cooking. All the common vegetables, such as potatoes, turnips, carrots, beets, and the different grains, such as rice, wheat, corn, oats, etc., neither taste good nor are easily digestible until their starch, cellulose, and other constituents have been changed from their compact indigestible form by the action of heat. Some one has spoken of cooking as a sort of artificial digestion, by which nature is relieved of a certain amount of work which it would be very difficult, if not impossible, for her to perform.

=Flavors.= The necessity of cooking to develop, or to create, a palatable taste is important. The flesh of fowl is soft enough to masticate, but only a person on the verge of starvation could eat it until heat has changed its taste and made it one of the most savory and acceptable of meats. Coffee also well illustrates this point. When coffee is green--that is, unbrowned--it is acrid in taste, very tough, even horny in consistency, and a decoction made from it is altogether unpleasant. But when it is subjected to a certain degree of heat, for a certain time, it loses its toughness, becomes brittle, changes color, and there is developed in it a most agreeable flavor. This flavoring property is an actual product of the heat, which causes chemical changes in an essential oil contained in the bean. Heat not only develops but creates flavors, changing the odor and taste as well as the digestibility of food.

=Effects of Cold.= Some foods are better for being cold; for example, butter, honey, salads, and ice-cream. Sweet dishes as a rule are improved by a low temperature. The flavor of butter is very different and very much finer when cold than when warm. It is absolutely necessary to keep it cool in order to preserve the flavor.

CHEMICAL AND PHYSICAL CHANGES

=Chemical Changes.= Since many of the changes which cooking produces in the different food materials are of a chemical nature, it is well to consider what constitutes a chemical process. This idea may perhaps be best conveyed by a few experiments and illustrations, the materials for which may be easily obtained.

=Exp. with Cream of Tartar and Bicarbonate of Soda.= Mix two
teaspoons of cream of tartar with one of bicarbonate of soda,
in a little warm water. A union of the two substances follows
and they neutralize each other; that is, the cream of tartar is
no longer acid, and the soda is no longer alkaline. Owing to
the power of chemical affinities a separation or breaking up of
these compounds takes place, and new substances, _carbonic acid_
and _rochelle salts_, are formed out of their constituents.
The effervescence which is seen is caused by the escape of the
carbonic acid.

=Exp. with Hydrochloric Acid and Soda.= Put a few drops of
chemically pure hydrochloric acid into a little water; then add
soda. A violent effervescence will follow. Continue putting in
soda until this ceases, when the reaction should be neutral.
Test it with litmus-paper. If it turns blue litmus-paper red, it
is acid; if red litmus-paper blue, it is alkaline. Add acid or
soda, whichever is required, until there is no change produced in
either kind of litmus-paper. The results of this experiment are
similar to those in the first one, namely, carbonic acid and a
salt. In this case the salt is _sodium chlorid_ or _common salt_,
which is in solution in the liquid. Evaporate the water, when
salt crystals will be found.[3]

=Oxid of Iron.= A piece of iron when exposed to the weather
becomes covered with a brownish-yellow coating, which does not
look at all like the original metal. If left long enough it will
wholly disappear, being completely changed into the yellowish
substance, which is _oxid of iron_, a compound of oxygen and
iron, commonly called _iron rust_.

=Burning of Coal.= A piece of coal burns in the grate and is
apparently destroyed, leaving no residue except a little ashes.
The carbon and hydrogen of the coal have united with the oxygen
of the air, the result of which is largely the invisible gas,
_carbonic acid_, which escapes through the chimney.

=Formation of Water.= Water is formed by the union of two
invisible gases, hydrogen and oxygen. It bears no resemblance
whatever to either of them. Its symbol is H_{2}O.

All these are examples of chemical changes.

=Definition of Chemical Change.= Chemical changes or processes may be defined as those close and intimate actions amongst the particles of matter by which they are dissociated or decomposed, or by which new compounds are formed, and involving a complete loss of identity of the original substance.

=Physical Changes.= Mix a teaspoon of sugar with an equal amount
of salt; the sugar is still sugar, and the salt remains salt; and
they may each be separated from the mixture as such.

Water when frozen is changed from a liquid to a solid; its
chemical composition, however, remains unchanged.

Water converted into steam by heat is changed from a liquid to
a gas, but chemically there is no difference between the one and
the other. _Steam_, _water_, and _ice_ are forms of the same
substance, the difference being physical, not chemical, and
caused by a difference in temperature.

Lead melted so that it will run, and the solid lead of a bullet,
are the same thing.

These illustrate physical changes.

=Definition.= When substances are brought together in such a way that their characteristic qualities remain the same, the change is called physical. It is less close and intimate than a chemical change. The transition from one state into another is also frequently only a physical change, as is seen in the transformation of water into steam, water into ice, etc.

ELEMENTS

One feature of the work of the chemist is to separate compound bodies into their simple constituents. These constituents he also endeavors to dissociate; and if this cannot be done by any means known to him, then the thing must be regarded as a simple substance. Such simple bodies are called _elements_.

=Definition.= An element then may be defined as a simple substance, which cannot by any known process be transformed into anything else; that is, no matter how it is treated, it still remains chemically what it was before. Gold, silver, copper, iron, platinum, carbon, phosphorus, calcium, oxygen, hydrogen, nitrogen, and chlorin are examples of elements. Once it was believed that there were but four elements in the world--earth, air, fire, and water. Then it was learned that these were not elements at all, but compounds, and the number of elements increased, until now sixty-eight are admitted to be simple primary substances. Some of these may in the future be proven to be compounds. Sulphur is at present in the doubtful list.

=Oxygen.= Oxygen is an element. It is an invisible gas, without taste or smell. It is the most abundant substance in the world, and an exceedingly active agent, entering into nearly all chemical changes and forming compounds with all known elements except one--fluorin. It is a necessity of life and of combustion.[4] It constitutes about two thirds of the weight of our bodies and one fifth of the weight of the air.

=Hydrogen.= Hydrogen is a gas. It is the lightest substance known. It unites with oxygen to form water, and, as will be seen later, enters into the composition of the human body.[5]

=Nitrogen.= Nitrogen is also a gas, but, unlike oxygen, is an inactive element. It supports neither fire nor life. It is not poisonous, however, for we breathe it constantly in the atmosphere, where its office is to dilute the too active oxygen. A person breathing it in a pure state dies simply from lack of oxygen.

=Carbon.= Carbon is a solid and an important and abundant element. It is known under three forms: diamond, graphite, and charcoal. The diamond is nearly pure carbon. Graphite (the "black-lead" of lead-pencils), coal, coke, and charcoal are impure forms of it. Carbon is combustible; that is, it burns or combines with oxygen. In this union carbonic acid is formed, and there is an evolution of heat, and usually, if the union be rapid and intense enough, of light. It is the valuable element in fuels, and in the body of man it unites with the oxygen of the air, yielding heat, to keep the body warm, and energy or muscular strength for work (Prof. Atwater). The carbonic acid formed in the body is given out by the lungs and skin.

=Other Elements.= There are many other elements about which it would be interesting to note something, such as calcium and phosphorus (found abundantly in the bones), magnesium, sulphur, sodium, iron, etc. Samples of these may be obtained to show to pupils, and descriptions given and experiments made, at the discretion of the teacher. Of the four most abundant elements of the body and of food,--oxygen, carbon, hydrogen, and nitrogen,--it is extremely important that some study be made, and if the apparatus can be procured, that it be of an experimental nature rather than simply descriptive.[6]

AIR

Air is made up principally of two elements, nitrogen and oxygen. It also always contains vapor of water and carbonic acid. Its average composition is as follows:

Nitrogen 78.49%
Oxygen 20.63%
Aqueous Vapor .84%
Carbonic Acid .04%

These are mixed together, not _chemically united_. Oxygen and nitrogen do unite chemically, but not in the proportions in which they exist in the air. Nitrous Oxid (N_{2}O), sometimes called "Laughing Gas," is one of the compounds of nitrogen and oxygen.

FIRE

=Exp. with a Candle.= Take a tallow candle, and by means of a
lighted match raise its temperature sufficiently high to start an
action between the carbon in the candle and the oxygen of the
air; in other words, light the candle. A match is composed of
wood, sulphur, and phosphorus. The latter is a substance which
unites with oxygen very easily; that is, at a _low temperature_.
By friction against any hard object, sufficient heat is aroused
to effect a union between the phosphorus of a match and the
oxygen of the surrounding air; the flame is then conveyed to
the sulphur, or the heat thus generated causes a union between
it (the sulphur) and the oxygen, sulphur burning somewhat less
freely than phosphorus; this gives enough heat to ignite the
wood, and with its combustion we get sufficient heat to light
the candle, or to start a chemical union between the combustible
portion, carbon chiefly, of the candle and the oxygen of the air.
Allow the candle to burn for a time, then put over it a tall
lamp-chimney; notice that the flame grows long and dim. Next
place on the top of the chimney a tin cover, leaving a small
opening, and make an opening into the chimney from below, with
a pin or the blade of a knife placed between it and the table;
note that the candle burns dimly. Then exclude the flow of air by
completely covering the top; in a moment, as soon as the oxygen
inside the chimney is consumed, the candle will go out.

This shows (1) that air--in other words, oxygen--is necessary to cause the candle to burn; (2) that by regulating the draft or flow of air the intensity of the combustion may be increased or diminished; (3) that by completely excluding air the candle is extinguished. This experiment with the candle illustrates the way in which coal is consumed in a stove. By opening the drafts and allowing the inflow of plenty of oxygen, combustion is increased; by partially closing them it is diminished, and by the complete exclusion of air burning is stopped.

The products of the burning of coal are carbonic acid and a small amount of ash. Twelve weights of coal, not counting the ash, will unite with thirty-two weights of oxygen, giving as a result forty-four weights of carbonic acid. Accompanying the union there is an evolution of light and heat. The enormous amount of carbonic acid given out daily from fires is taken up by plants and used by them for food. In the course of ages these plants may become coal, be consumed in combustion, and, passing into the air, thus complete the cycle of change.

=Fuel and Kindlings.= The common fuels are coal, coke, wood, gas, coal-oil, and peat. For kindling, newspaper is good because, being made of straw and wood-pulp, it burns easily, and also because printers' ink contains turpentine, which is highly inflammable.

COMPOSITION OF THE BODY

Before entering upon the study of foods it is well to consider the composition of the human body, that some idea of its chemical nature may be gained. In the United States National Museum at Washington may be found some interesting information on this subject. From there much that is contained in the following pages is taken.

A complete analysis of the human body has never been made, but different organs have been examined, and chemists have weighed and analyzed portions of them, and from such data of this nature as could be obtained, estimates of the probable composition of the body have been calculated. Thirteen elements united into their compounds, of which there are more than one hundred, form it.

The following table gives the average composition of a man weighing 148 pounds.

Oxygen 92.4
Carbon 31.3
Hydrogen 14.6
Nitrogen 4.6
Calcium 2.8
Phosphorus 1.4
Potassium .34
Sulphur .24
Chlorin .12
Sodium .12
Magnesium .04
Iron .02
Fluorin .02
PROF. ATWATER.

It will be seen from this that oxygen, carbon, hydrogen, and nitrogen constitute nearly the whole, the other elements being in very small proportions.

PRINCIPAL CHEMICAL COMPOUNDS IN THE BODY

The following interesting table, obtained at the National Museum, gives the principal compounds of the body. Some of the more rare organic compounds are omitted.

WATER:--A compound of oxygen and hydrogen.

PROTEIN { _ALBUMINOIDS_ { MYOSIN AND SYNTONIN OF MUSCLE
COMPOUNDS, { or { (sometimes called "muscle
{ _Proteids_. { fibrin").
composed { { Albumen of blood and milk. Casein
mainly of { { of milk.
{
{ { Collagen of bone and }
_Carbon_, { { tendons. } which
{ _Gelatinoids._ { Chondrigen of cartilage, } yield
_Oxygen_, { { gristle, } gelatin.
{
_Hydrogen_, { {
{ _Hemoglobin._ { The red coloring matter of blood.
_Nitrogen_. { {

FATS, { { } These make up the
{ { Stearin, } bulk of the fat of
composed { _Neutral { } the body.
mainly of { Fats._ { Palmitin, } They are likewise
{ { } the chief
{ { Olein, etc. } constituents of
_Carbon_, { { } tallow, lard, etc.
{
_Oxygen_, { _Complex { Protagon, } Found chiefly in
{ Fats_, { } the brain, spinal
_Hydrogen_, { containing { Lecithin, } cord, nerves, etc.
{ phosphorus { }
{ and nitrogen. { Cerebrin. }

CARBOHYDRATES, { Glycogen, "animal starch." Occurs in the
composed { liver and other organs.
of { Inosite, "muscle sugar." Occurs in various
_Carbon_, { organs.
_Oxygen_, { Lactose, "milk sugar." Occurs in milk.
_Hydrogen_. { Cholesterin. Occurs in brain, nerves, and other
{ organs.

{ Phosphate of lime, or calcium }
{ phosphate. } Occurs chiefly
{ Carbonate of lime, or calcium } in bones and
{ carbonate. } teeth, though
{ Fluorid of calcium, or calcium } found in
{ fluorid. } other organs.
{ Phosphate of magnesia, or }
{ magnesium phosphate. }
{

MINERAL { PHOSPHATE OF POTASH, OR POTASSIUM }
SALTS. { phosphate. }
{ Sulphate of potash, or potassium } Distributed
{ sulphate. } through the
{ Chlorid of potassium, or } body in the
{ potassium chlorid. } blood, muscle,
{ Phosphate of soda, or sodium } brain,
{ phosphate. } and other
{ Sulphate of soda, or sodium } organs.
{ sulphate. }
{ Chlorid of sodium, or sodium }
{ chlorid. }

Now, since the body is composed of these substances, our food, including air and water, should contain them all in due proportion, that the growth, energy, and repair of the body may be healthfully maintained.

THE FIVE FOOD PRINCIPLES

For convenience of comparison foods may be divided into five classes: Water, Protein, Fats, Carbohydrates, Mineral Matters.

Some scientists include air in the list, but it has been thought best in this work to speak of it separately as the greatest necessity of life, but not in the sense of a direct nutrient.

An average composition of three of the principles is as follows:

{ Carbon 53
PROTEIN { Hydrogen 7
{ Oxygen 24
{ Nitrogen 16

{ Carbon 76.5
FATS { Hydrogen 12
{ Oxygen 11.5
{ Nitrogen --

{ Carbon 44
CARBOHYDRATES { Hydrogen 6
{ Oxygen 50
{ Nitrogen --

It will be seen from the above that the protein compounds contain nitrogen; the fats and carbohydrates do not.

WATER

We will now consider the first of the food principles--water. Water is one of the necessities of life. A person could live without air but a few minutes, without water but a few days. It constitutes by weight three fifths of the human body, and enters largely into all organic matter. Water is an aid to the performance of many of the functions of the body, holding in solution the various nutritious principles, and also acting as a carrier of waste. It usually contains foreign matter, but the nearer it is to being pure the more valuable it becomes as an agent in the body. Ordinary hydrant, well, or spring water may be made pure by filtering and then sterilizing it.

=Exp.= Put a little water into a test-tube, and heat it over
the flame of an alcohol-lamp. In a short time tiny bubbles will
appear on the sides of the glass. These are not steam, as may
be proved by testing the temperature of the water; they are
bubbles of atmospheric gases which have been condensed in the
water from the air; they have been proved to be nitrogen, oxygen,
and carbonic acid, but as they do not exist in the water in the
same proportions as in the air, they are not called _air_, but
_atmospheric gases_. Continue the heating, and the bubbles will
continue to form. After a while, very large bubbles will appear
at the bottom of the tube; they increase rapidly and rise toward
the top; some break before reaching it, but as the heat becomes
more intense others succeed in getting to the surface,--there
they break and disappear. If the water now be tested with a
thermometer, it will be found to have reached 212° Fahrenheit or
100° Centigrade, provided the experiment be tried at or near the
level of the sea.

=Steam.= The large bubbles are bubbles of steam, or water expanded by heat until its particles are so far apart that it ceases to be a liquid and becomes a gas. True steam is invisible; the moisture which collects on the sides of the tube and is seen coming out at the mouth is partially condensed steam, or watery vapor. Watch a tea-kettle as it boils on a stove; for the space of an inch or two from the end of the spout there seems to be nothing; that is where the _true_ steam is; beyond that, clouds of what is commonly called steam appear; they are watery vapor formed from the true steam by partial condensation which is produced by its contact with the cool air.[7]

=Boiling-point of Water.= Water boils at different temperatures, according to the elevation above the sea-level. In Baltimore it boils practically at 212° Fahr.; at Munich in Germany at 209½°; at the city of Mexico in Mexico at 200°; and in the Himalayas, at an elevation of 18,000 feet above the level of the sea, at 180°. These differences are caused by the varying pressure of the atmosphere at these points. In Baltimore practically the whole weight of the air is to be overcome. In Mexico, 7000 feet above the sea, there are 7000 feet less of atmosphere to be resisted; consequently, less heat is required, and boiling takes place at a lower temperature. By inclosing a vessel of water in a glass bell, and exhausting the air by means of an air-pump, water may be made to boil at a temperature of 70° Fahr., showing that much of the force (heat) that is consumed in causing water to be converted into steam is required to overcome the pressure of the air. The foregoing illustrates the point that _boiling water_ is not of invariable temperature; consequently, that foods which in some places are cooked in it may in other places be cooked in water that is not boiling,--in other words, that it is not ebullition which produces the change in boiling substances, but heat.

=Changes Produced in Water by Boiling.= By boiling water for a moderate time the greater part of the atmospheric gases is driven off. The flavor is much changed. We call it "flat"; but by shaking it in a carafe or other vessel so that the air can mingle with it, it will reacquire oxygen, nitrogen, and carbonic acid, and its usual flavor can thus be restored.

Water which flows through soil containing lime is further changed by boiling.

=Exp. with Lime-water.= Pour a little lime-water into a
test-tube. With a small glass tube blow into it for a few
minutes, when it will become milky; continue the blowing for a
few minutes more, when it will lose its cloudy appearance and
become clear again. The following explains this: in the first
place there was forced into the lime-water, from the lungs, air
containing an excess of carbonic acid; this united with the lime
in solution in the water and formed carbonate of lime. Carbonate
of lime is insoluble in water which contains no carbonic acid, or
very little,[8] but will dissolve in water which is charged with
it, and this is produced by the continued blowing. Now if this
water be freed of its excess of carbonic acid by boiling, the
carbonate of lime will be freed from its soluble state, and will
fall as a precipitate and settle on the sides of the vessel. From
this we learn that water may be freed from carbonate of lime in
solution in it by boiling.

=Organic Matter in Water.= There is another class of impurities in water of vastly more importance than either the atmospheric gases or lime. These are the organic substances which it always contains, especially that which has flowed over land covered with vegetation, or that which has received the drainage from sewers. The soluble matter found in such water is excellent food for many kinds of micro-organisms which often form, by their multiplication, poisons very destructive to animal life. Or the organisms themselves may be the direct producers of disease, as for instance the typhoid fever bacillus, the bacillus of cholera, and probably others which occur in drinking-water. These organisms are destroyed by heat, so that the most valuable effect produced in water by boiling it is their destruction. Such water is, therefore, a much safer drink to use than that which has not been boiled. Water should always be boiled if there is the slightest suspicion of dangerous impurities in the supply.

=Use of Tea and Coffee.= This leads us to the thought that the extensive use of tea and coffee in the world may be an instinctive safeguard against these until recently unknown forms of life. The universal use of cooked water in some form in China is a matter of history. The country is densely populated, the sewage is carried off principally by the rivers, so that the danger of contracting disease through water must be very great, and it is probable that instinct or knowledge has prompted the Chinaman to use but very little water for food except that which has been cooked. Whatever the reason, the custom is a national one. The every-day drink is weak tea made in a large teapot and kept in a wadded basket to retain the heat; the whole family use it. The very poor drink plain hot water or water just tinged with tea.

That tea and coffee furnish us each day with a certain amount of wholesome liquid in which all organic life has been destroyed, remains a fact; they may be, in addition, when _properly made_ and of _proper strength_, of great value on account of their warmth, good flavor, and invigorating properties. There is no doubt that it is of the greatest importance that tea and coffee be used of _proper strength_; for if taken too strong, disorders of the system may be produced, necessitating their discontinuance, and thus depriving the individual of a certain amount of warm and wholesome liquid.

=To Summarize.= The effects produced in water by boiling which have been spoken of are: (1) the expulsion of the atmospheric gases; (2) the precipitation of lime when in solution; and (3) the destruction of micro-organisms. The most important points to remember in connection with water are, that a certain amount each day is an absolute necessity of life, and that unless the supply be above suspicion it should be filtered and then sterilized.

=Filtration and Sterilization of Water.= Filtration as a general thing is done by public authorities, but sterilization is not, and should be done when necessary by the nurse. For immediate use, simply boiling is said on good authority to be sufficient to destroy all _organisms_ then in the water. _Spores_ of organisms are, however, not killed by boiling, as they are very resistant to heat. Fortunately they are not common. As they do not develop into bacteria for some hours after the water has been boiled, they may be entirely gotten rid of by allowing them to develop and then destroying by a second boiling; but for all practical purposes, and under ordinary circumstances, water is rendered safe for use by boiling it once.[9] Should the water be very bad, boil it in a jar plugged with cotton for half an hour three days in succession, keeping it meanwhile in a temperature of 70° or 80° Fahr., so that any _spores_ of organisms which may be in it will have an opportunity to get into such a state of existence that they will be capable of being killed by the next boiling. The third treatment is for the purpose of making sure of any that may have escaped the first and second.

PROTEIN

The second of the food principles, protein, is a complex and very important constituent of our food. The protein compounds differ from all others as to chemical composition by the presence of nitrogen; they contain _carbon_, _oxygen_, _hydrogen_, and _nitrogen_, while the fats and carbohydrates are composed principally of _carbon_, _oxygen_, and _hydrogen_, but no nitrogen. The so-called extractives or flavoring properties of meats are nitrogenous, and are consequently classed with the protein compounds.[10]

The body of an average person contains about _eighteen_ per cent. of protein. The proteins of various kinds furnish nutriment for blood and muscle, hence the term "muscle-formers," which is sometimes given them. They also furnish material for tendons and other nitrogenous tissues. When these are worn out by use, it is protein which repairs the waste.

Most of the valuable work upon the analysis of food has been done in Germany. From estimates made by chemists of that country it has been decided that the amount of protein in a diet should not fall below _four ounces daily_. This is to represent an allowance for a man of average weight doing an average amount of work, below which he cannot go without loss in health, in work, or in both. Although protein is the most expensive of all food materials, one should endeavor to use at least four ounces each day. Meat, milk, eggs, cheese, fish of all kinds, but especially dried cod, wheat, beans, and oatmeal are all rich in this substance. The protein compounds are divided into three classes:

ALBUMINOIDS, GELATINOIDS, EXTRACTIVES.

=Albuminoids.= The most perfect type of an albuminoid is the white of egg. It is a viscous, glairy, thick fluid which occurs also in the flesh of meat as one of its juices, in fish, in milk, in wheat as gluten, and in other foods. It is soluble in cold water.

=Exp.= Mix some white of egg in a tumbler with half a cup of cold
water. As soon as the viscousness is broken up it will be found
to be completely dissolved. It is insoluble in alcohol.

=Exp.= Pour upon some white of egg double its bulk of alcohol. It
will coagulate into a somewhat hard opaque mass.

Heat also has the power of coagulating albumen.

=Coagulation of Albumen by Heat.= Put into a test-tube some white
of egg, and place the tube in a dish of warm water. Heat the
water gradually over a gas-flame or an alcohol-lamp. When the
temperature reaches 134° Fahr. it will be seen that little white
threads have begun to appear; continue the heating to 160°, when
the whole mass becomes white and firm. Now remove a part from the
tube and test its consistency; it will be found to be tender,
soft, and jelly-like. Replace the tube in the dish of water
and raise the heat to 200° Fahr.; then take out a little more
and test again; it will now be found hard, close-grained, and
somewhat tough. Continue the heating, when it will be seen that
the tenacity increases with rise of temperature until at 212°
Fahr., the boiling-point of water, it is a firm, compact solid.
When heated to about 350°, white of egg becomes so tenacious that
it is used as a valuable cement for marble.

These experiments illustrate a very important point in the cooking of albuminous foods. They show that the proper temperature for albumen is that at which it is thoroughly coagulated, but not hardened; that is, about 160° Fahr. Most kinds of meat, milk, eggs, oysters, and fish, when cooked with reference to their albumen alone, we find are also done in the best possible manner with reference to their other constituents. For instance, if you cook an oyster thinking only of its albuminous juice, and endeavor to raise the temperature throughout all of its substance to, or near, 160° Fahr., and not higher, you will find it most satisfactory as to flavor, consistency, and digestibility. The same is true of eggs done in all ways, and of dishes made with eggs, such as custards, creams, and puddings. With the knowledge that albumen coagulates at a temperature of 52° below that of boiling water, one can appreciate the necessity of cooking eggs in water that is not boiling, and a little experiment like the above will impress it upon the mind as no amount of mere explanation can possibly do.

The cooking of eggs, whether poached, cooked in the shell, or in omelets, is of much importance, for albumen when hard, compact, and tenacious is very difficult of digestion; the gastric juice cannot easily penetrate it; sometimes it is not digested at all; while that which is properly done--cooked in such a way that it is tender and falls apart easily--is one of the most valuable forms of food for the sick.

Albumen should always be prepared in such manner as to require the least possible expenditure of force in digestion. Those who are ill cannot afford to waste energy. Whether they are forced to do so in the digestion of their food depends very much upon the person who prepares it.

Advantage is often taken, in cooking, of the fact that albumen hardens on exposure to certain degrees of heat, to form protecting layers over pieces of broiling steak, roast meats, etc. If a piece of meat is placed in cold water to cook, it is evident, since albumen is soluble in cold water, that some of it will be wasted. If the same piece is plunged into boiling water the albumen in its outer layers will be immediately hardened, and form a sheath over the whole which will keep in the juices and the very important flavors. When broth or soup is made, we put the meat (cut into small pieces to expose a large extent of surface) into cold water, because we wish to draw out as much as possible the soluble matter and the flavors. If, on the other hand, the meat is to be served boiled, and broth or soup is not the object, then this order should be reversed, and every effort made to prevent the escape of any of the ingredients of the meat into the liquid.

In broiling steak, we sacrifice a thin layer of the outside to form a protecting covering over the whole by plunging it into the hottest part of the fire, so that the albumen will become suddenly hard and firm, and plug up the pores, thus preventing the savory juices from oozing out. More will be said on this subject in the recipes for cooking these kinds of foods.

=Gelatinoids.= The second class of protein compounds comprises the gelatinoids, gelatin being their leading constituent. It is found in flesh, tendons, cartilage and bone; in fact, it exists in all the tissues of the body, for the walls of most of the microscopic cells of which the tissues are composed contain gelatin.

=Exp.= Boil a pound of lean meat freed from tendons, fat, and
bone, in a pint of water for three hours; then set the liquid
away to cool. Jelly resembling calf's-foot jelly will be the
result. The cell-walls of the flesh have been dissolved by the
long-continued action of heat and liquid. This is commonly called
stock or glaze.

=Exp.= Put a piece of clean bone into a dilute solution of
hydrochloric acid. In two or three days the acid will have acted
upon the earthy matters in the bone to remove them, and gelatin
will remain. The average amount in bone is about thirty per cent.

Calves' feet were formerly used for jelly because of the excess of gelatin which they contain. They were cooked in water for a long time and the liquid reduced by further boiling; it was then clarified, flavored, and cooled; the result was a transparent, trembling jelly. The prepared gelatin of commerce, or _gelatine_, has now largely displaced this, for it is much more convenient to use, and less expensive.

=Extractives.= The extractives or flavoring properties of meats and other substances are usually classed with the protein compounds. Their chemical nature is not well understood.

FATS

=Fixed and Volatile Oils.= There are two classes of fats, called _fixed oils_ and _volatile oils_. All kinds of fats good for food belong to the class of fixed oils. A volatile oil is one which evaporates away, like alcohol or water, and leaves no residue. The fixed oils, at least most of them, will not do this; they do not vaporize even at very high temperatures, but they become dissociated or decomposed,--that is, their chemical structure is broken up before their boiling-point is reached. Volatile oils, on the contrary, are capable of being boiled and transformed into gases. Some one illustrates this by the changes which take place in water. When water is heated to 212° Fahr. it is converted into a gas, which on cooling below 212° returns to the liquid state again without loss. The essential oil, turpentine, if heated to 320° Fahr. ceases to be a liquid and becomes a gas, which on cooling becomes a liquid oil again without loss of weight. Other volatile oils are oil of cloves, oil of bitter almonds, orange and lemon oil, oil of cinnamon, bergamot, and patchouli.

The boiling sometimes noticed in a pot of lard is owing to the presence in it of a little water which is very soon converted into steam, when the bubbling ceases, and after that the temperature of the fat rises rapidly, reaching in a short time four or five hundred degrees Fahrenheit, when a separation of its constituents takes place, and carbon is revealed as a black mass.

=Composition of Fats.= Fats are _hydrocarbons_--that is, they are composed chiefly of carbon united with hydrogen and oxygen. They must not be confounded with the _carbohydrates_, which are always composed of carbon with the elements of water--that is, the proportion of hydrogen to oxygen is as two to one,--whereas in the hydrocarbons this is not the case. These elements enter into the compositions of fats as various fatty acids and glycerin; the acids are not sour, as one would suppose from the name, but are so called because they behave chemically toward bases as sour acids do, that is, they unite with them. The glycerin of commerce is obtained by decomposing fats.

=Fat in Milk.= The white color of milk is given to it by minute globules of fat suspended in it.

=To prove this=: Put a little milk into a bottle with a
ground-glass stopper; pour upon it three times its bulk of ether
and shake gently; let it stand for two or three days, when it
will be found that the ether has dissolved the fat and left a
semi-transparent yellowish white liquid resembling blood serum.
By pipetting or carefully pouring off the ether, and evaporating
it by placing the vessel containing it in a dish of warm water,
clear oil will be obtained. Care must be taken not to put the
ether near a flame or the fire, as it is highly inflammable, and
an explosion might occur. Ether boils at 94.82° Fahr.

The proportion of fat in milk is from 2.8 to 8 per cent. It varies in milk from different species of cows, and from the same species at different times, according to age, feeding, and other circumstances.

=Cream.= When milk is allowed to stand without disturbance for a time the globules of fat, being lighter than water, rise to the surface and form cream. Cream is the most wholesome, palatable, and easily digested form of fat. Butter is obtained by beating milk or cream in a churn until the little globules of fat break and stick together in a mass.

=Olive-Oil.= Olive-oil is one of the most easily digested and palatable of fats. A genuine oil of the first quality is, in this country unfortunately, expensive, much of that sold under the name being adulterated with cotton-seed oil, poppy-oil, and essence of lard.[11]

Cotton-seed oil has no especially bad flavor, but it is unpleasant and indigestible when used raw as in sardines and salads. The after taste which it leaves reminds one too forcibly of castor-oil.

Olive-oil of the best quality is almost absolutely without flavor. It is prepared in several grades: the first pressing from the fruit is the best, the second is fair, the third inferior, and there is sometimes a fourth known as refuse oil. For deep fat frying nothing is so good as olive-oil, but its costliness in this country excludes it from common use.

The fat of the sheep and ox, after it has been rendered, and deprived of all membrane and fibers, is called _tallow_. The term is also applied to the fat of other animals, and to that of some plants, as bayberry-tallow, piny tallow, and others. The uncooked fat of any animal is called _suet_, but the name has come to be applied to the less easily melted kinds, which surround the kidneys or are in other parts of the loin. The fat which falls in drops from meat in roasting is called _dripping_.

THE CARBOHYDRATES

=Starch.= Starch is a substance found in wheat, corn, oats, and in fact in all grains, in potatoes, in the roots and stems of many plants, and in some fruits. In a pure state it is a white powder such as is seen in arrowroot and corn-starch. Examined by a microscope this powder is found to be made up of tiny grains of different shapes and sizes, some rounded or oval, others irregular. Those of potato-starch are ovoid, with an outside covering which appears to be folded or ridged, and looks somewhat like the outside of an oyster-shell, although its similarity extends no further than appearance, as the little ridges are true folds, and not overlapping edges.

=Size of Starch Grains.= Starch grains vary in size according to the source from which the starch is obtained. Those of ground rice are very small, being about 1/3000 of an inch in diameter; those of wheat are 1/1000 of an inch, and those of potato 1/300 of an inch.

Starch is a carbohydrate, being composed of six parts of carbon, ten of hydrogen, and five of oxygen. Its symbol is C_{6}H_{10}O_{5}. It is insoluble in water, but when the water is heated, the grains seem to absorb it; they increase in size, the ridges or folds disappear, and when the temperature reaches 140° Fahr. or a little over, they burst, and the contents mingle with the liquid forming the well-known paste.

=Test for Starch.= Mix a teaspoon of starch with a cup of cold
water and boil them together for a few minutes until a paste is
formed; then set it aside to cool. Meanwhile make a solution of
iodine by putting a few flakes into alcohol, or use that which is
already prepared, and which may be obtained at any pharmacy. Add
a drop of this solution to the paste mixture; it will immediately
color the whole a rich dark blue. This is known as the "iodine
test," and is a very valuable one to the chemist, for by means of
it the slightest trace of starch can be detected.

=Exp. with Arrowroot.= Make a thin paste by boiling a little
arrowroot and water together. When cool test it with a drop of
the iodine solution. The characteristic blue color will be very
strong, showing that arrowroot is rich in starch.

Similar tests may be made with grated potato, wheat-flour, rice-flour, tapioca, and other starch-containing substances. Also powdered sugar, cream of tartar, and other substances may be tested, when it is suspected that they have been adulterated with starch.

Although starch grains burst and form a paste with water at 140° Fahr., that is not the temperature at which it should be cooked for food, and the thickening which then takes place should not be confounded, as often happens, with the true cooking of starch. In order to understand the difference between the proper cooking of starch and the simple bursting of the grains, let us consider the changes which take place in starch when it is subjected to different degrees of heat, and also those which are produced in it during the process of digestion. All starch in food is changed into dextrine and then into sugar (glucose, C_{6}H_{12}O_{6}) in the process of digestion. Glucose is a kind of sugar, resembling cane-sugar, but it is not so sweet.

=Dextrine.= Dextrine is a substance having the same chemical nature as starch, but differing in many of its properties. It may be described as a condition which starch assumes just before its change into glucose.

=Exp. to show Dextrine.= Carefully dry and then heat a little
starch to about 400° Fahr. Keep it at this temperature until it
turns brown, or for ten minutes. Then mix it with water, when it
will dissolve, forming a gummy solution. Starch will not do this.
Test it with iodine; it will not change color. The remarkable
thing about the relation of dextrine to starch is that although
they differ so much in properties they have the same chemical
composition.

The change of starch into dextrine is an important point in cooking, because starch cannot be assimilated until the conversion has taken place, either before or after it is eaten. Now it will be seen that unless this change is either produced or approached in the cooking of starch-containing foods, they are not prepared as well as it is possible to prepare them; also, that it is not possible to cause this change at a low temperature; therefore 140° (the temperature at which the grains burst) should not be regarded as the cooking temperature of starch. It should be such a temperature as shall actually convert it into dextrine, or at least change it to such an extent that it will be more easily converted into dextrine, and ultimately into sugar, by the digestive fluids. This should be as near 401° Fahr. as practicable,--not that a potato, or a loaf of bread, or a pudding will have all the starch in it changed when it is put into an oven of that temperature. It would not be possible, on account of the water contained in each; but that in the outside may be, and the preparation of the remainder will be better than at a lower temperature.

There are other means of changing starch into dextrine than by heat, one of the most remarkable of which is _diastase_, a substance found in sprouting grains, which has the power to transform the starch stored in the grain by nature into soluble dextrine, in which form it can be taken up by the young plant for food. The crude starch could not thus be absorbed. The starch which we use as food is of no more value to us than it is to the young plant until it has been changed into dextrine or sugar. Now, if art outside of the body can accomplish what nature is otherwise forced to do in the alimentary canal, the body will be saved a certain amount of force,--a point of great importance, especially in the case of the sick or invalid, who can ill afford to waste energy.

Starch constitutes half of bread, our "staff of life"; nearly all of rice, the staff of life in the East; and the greater part of corn-starch, sago, arrowroot, tapioca, peas, beans, turnips, carrots, and potatoes.

_Arrowroot_ is the purest form of starch food known. _Rice_ is richest in starch of all the grains. _Tapioca_ is prepared from the root of a tropical plant; it is first crushed and the grains washed out with water, then the whole is heated and stirred, thus cooking and breaking the starch grains, which on cooling assume the irregular rough shapes seen in the ordinary tapioca of commerce. Probably a part of the starch is converted into dextrine, which accounts for the peculiarly agreeable flavor which tapioca possesses. Mixed with the grains, as they are taken from the plant, is a very dangerous poison which, being soluble in water and volatile, is partially washed away and partially driven out by the heat,--in fact the heating is done for this purpose. _Sago_ is principally starch. It is obtained from the pith of the sago-palm. Imitations of both tapioca and sago are sometimes made from common starch.

Starch may be converted into grape-sugar by treating it with acids; that of corn is generally used for the purpose. Much of the glucose of commerce is made in this way. In the United States it is estimated that $10,000,000 worth is manufactured every year. It is used for table syrup, in brewing beer, in the adulteration of cane-sugar, and in confectionery. Honey is also made from it. The nutritive value of vegetables is due largely to the starch and sugar which they contain.

In the economy of the body starch is eminently a heat producer. Pound for pound it does not give as much heat as fat, but owing to its great abundance and extensive use it, in the aggregate, produces more. (Atwater.)

Starch is an abundant and easily digested form of vegetable food, but it is incapable of sustaining life. It contains none of the nitrogenous matter needed for the nutrition of the muscles, nerves, and tissues. Indeed, it is said on good authority that many an invalid has been slowly starved to death from being fed upon this material alone.

=Sugar.= There are many kinds of sugar, the most familiar of which is _cane-sugar_, or _sucrose_ (C_{12}H_{22}O_{11}). It is obtained from the juices of various plants, for instance, sugar-cane, beet-root, the sugar-maple, and certain kinds of palms. By far the greatest amount comes from the sugar-cane. It is made by crushing the stalks of the plant (which somewhat resembles Indian corn) and extracting the sweet juice, which is then clarified and evaporated until, on cooling, crystals appear in a thick liquid; this liquid is molasses, and the grains or crystals are brown sugar. White sugar is obtained by melting this brown sugar in water, removing the impurities, and again evaporating in vacuum-pans, which are used for the purpose of boiling the liquid at a lower temperature than it could be boiled in the open air, thus avoiding the danger of burning, and otherwise preserving certain qualities of the sugar. _Loaf-sugar_ is made by separating the crystals from the liquid by draining in molds; and _granulated_ sugar by forcing out the syrup in a centrifugal machine. The process of making beet-root sugar is similar. Sugar from maple sap is obtained by simply evaporating away the excess of water. In the East a considerable quantity of sugar is made from the juices of certain varieties of palm, especially the date-palm. Maple-sugar and palm-sugar are generally not purified.

Sucrose dissolves readily in water. By allowing such a solution to stand undisturbed for a time until the water has disappeared, transparent crystals are obtained, known as _rock candy_. Again, sucrose melted at a temperature of 320° Fahr. forms, on cooling, a clear mass, called _barley-sugar_. Heated to 420° Fahr. dissociation of the carbon from the water of crystallization takes place, the carbon appearing in its characteristic black color. This dark brown, sweetish-bitter syrup is called _caramel_. On cooling it forms a solid, which may be dissolved in water, and is used to color gravies, soups, beer, and so forth.

=Exp. with Sulphuric Acid.= A very pretty experiment to show the
separation of the water from the carbon may be made by treating
a little sugar in sulphuric acid. Put a tablespoon of sugar in
any vessel that will bear heat, a thin glass or stout cup. Pour
over enough concentrated sulphuric acid to thoroughly moisten it,
let it stand for a few minutes, when it will be seen that the
mass has changed color from white to a yellowish brown. The color
increases in intensity until it is perfectly black, when the
whole puffs and swells up, fumes are driven off, and a mass like
a cinder remains. This is charcoal, or nearly pure carbon.

The explanation is as follows: So strong is the affinity of the acid for the water that it breaks up the chemical combination between it and the carbon, unites with the water, and leaves the carbon free. So intense is the chemical change that an enormous amount of heat is evolved,--so much, in fact, that a considerable part of the water is vaporized, leaving the more or less solid charcoal. The light color noticed during the first part of the union indicates that the chemical dissociation is just beginning, and that only a small amount of carbon has been set free.

=Glucose.= Glucose or grape-sugar (C_{6}H_{12}O_{6}) is one of the kinds of sugar found in grapes, peaches, and other fruits. It is about two and one half times less sweet than cane-sugar. It is manufactured on a large scale from the starch of corn.

=Lactose.= Lactose or milk-sugar is the sugar found in the milk of the _Mammalia_. That of commerce comes chiefly from Switzerland, where it is made by evaporating the whey of cow's milk. For sweetening drinks for infants and for the sick, milk-sugar is said to be less liable to produce acid fermentation than cane-sugar, and also to be more easily digested.

Sugar is a valuable nutrient, being very easily digested and absorbed. Cane-sugar is converted into glucose in the process of digestion by the pancreatic juice, and after absorption it is completely utilized in the body, furnishing heat and probably energy.

=Effects of Heat on Sugar.= Sugar undergoes various changes, with different degrees of heat, by loss of some of its water of crystallization. One of the most remarkable of these is seen in caramel sauce, which is a rich crimson-brown syrup generally supposed to contain foreign coloring matter, but which does not. It is made by melting sugar without water, and heating it until the desired hue and thickness are reached. Nothing is added, but something is taken away; that is, some of the water is driven out, with the result of change in both color and taste.

In a recent article in "The Century Magazine" (November, 1891) Prof. Atwater touches upon the subject of the production of artificial foods from the crude materials of the earth, and states, among other things, that a sugar resembling fruit-sugar has been made artificially by synthesis, by Prof. Fischer of Würzburg, Germany.

AIR

Air is a gaseous elastic body which envelops the earth on every side, extending possibly two hundred miles from its surface, but all the while growing more and more rare as the distance increases. When pure it is tasteless and odorless. We really live at the bottom of an atmospheric ocean, and are pressed upon by its weight. At the sea-level the pressure upon every square inch of surface is equal to fifteen pound.