FIRE

Nitrogen78.49%Aqueous Vapor.84%Oxygen20.63%Carbonic Acid.04%

These are mixed together, notchemically united. Oxygen and nitrogen do unite chemically, but not in the proportions in which they exist in the air. Nitrous Oxid (N2O), sometimes called "Laughing Gas," is one of the compounds of nitrogen and oxygen.

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 oxygenof 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 alow 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 takenup 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.

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.

Oxygen92.4Sulphur.24Carbon31.3Chlorin.12Hydrogen14.6Sodium.12Nitrogen4.6Magnesium.04Calcium2.8Iron.02Phosphorus1.4Fluorin.02Potassium.34

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.

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 (sometimes called "muscle fibrin").Compounds,{or{{Proteids.{composed{{Albumen of blood and milk. Casein of milk.mainly of{{Carbon,{{Collagen of bone and tendons.}which{Gelatinoids.{}yieldOxygen,{{Chondrigen of cartilage, gristle,}gelatin.{Hydrogen,{{{Hemoglobin.{The red coloring matter of blood.Nitrogen.{{

Fats,{{Stearin,}These make up the bulk of the fat of the body.{Neutral{}composed{Fats.{Palmitin,}They are likewise the chief constituents of tallow, lard, etc.mainly of{{}{{Olein, etc.}Carbon,{{Complex{Protagon,}Found chiefly in the brain, spinal cord, nerves, etc.Oxygen,{Fats,{}{containing{Lecithin,}Hydrogen,{phosphorus{}{and nitrogen.{Cerebrin.}

Carbohydrates,{Glycogen, "animal starch." Occurs in the liver and other organs.composed of{Carbon,{Inosite, "muscle sugar." Occurs in various 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 in bones and teeth, though found in other organs.{Carbonate of lime, or calcium carbonate.}{Fluorid of calcium, or calcium fluorid.}{Phosphate of magnesia, or magnesium phosphate.}{Mineral{Phosphate of potash, or potassium phosphate.}Salts.{Sulphate of potash, or potassium sulphate.}Distributed through the body in the blood, muscle, brain, and other organs.{Chlorid of potassium, or potassium chlorid.}{Phosphate of soda, or sodium phosphate.}{Sulphate of soda, or sodium 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.

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 separatelyas 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:

{Carbon53Protein{Hydrogen7{Oxygen24{Nitrogen16{Carbon76.5Fats{Hydrogen12{Oxygen11.5{Nitrogen—{Carbon44Carbohydrates{Hydrogen6{Oxygen50{Nitrogen—

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

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 appearon 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 calledair, butatmospheric 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 thetruesteam 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 beovercome. 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 thatboiling wateris 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 beencooked. 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, whenproperly madeand ofproper 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 ofproper 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 allorganismsthen in the water.Sporesof 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 maybe 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 anysporesof 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.

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 containcarbon,oxygen,hydrogen, andnitrogen, while the fats and carbohydrates are composed principally ofcarbon,oxygen, andhydrogen, 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 abouteighteenper 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 belowfour 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.

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 thatlittle 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 easilypenetrate 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.

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, orgelatine, 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.

Fixed and Volatile Oils.There are two classes of fats, calledfixed oilsandvolatile oils. All kinds of fats good for food belong to the class of fixed oils. A volatile oil is one which evaporates away, like alcoholor 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 arehydrocarbons—that is, they are composed chiefly of carbon united with hydrogen and oxygen. They must not be confounded with thecarbohydrates, 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 basesas 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 calledtallow. 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 calledsuet, 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 calleddripping.

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 furtherthan 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 about13000of an inch in diameter; those of wheat are11000of an inch, and those of potato1300of an inch.

Starch is a carbohydrate, being composed of six parts of carbon, ten of hydrogen, and five of oxygen. Its symbol is C6H10O5. 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.

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 temperatureat 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, C6H12O6) 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 cookingtemperature 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 isdiastase, 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.

Arrowrootis the purest form of starch food known.Riceis richest in starch of all the grains.Tapiocais 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 andbreaking 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.Sagois 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 iscane-sugar, orsucrose(C12H22O11). 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-sugaris made by separating the crystals from the liquid by draining in molds; andgranulatedsugar 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 asrock candy. Again, sucrose melted at a temperature of 320° Fahr. forms, on cooling, a clear mass, calledbarley-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-bittersyrup is calledcaramel. On cooling it forms a solid, which may be dissolved in water, and is used to color gravies, soups, beer, and so forth.

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