Division of chemistry into organic and inorganic. Chemistry is usually divided into two great divisions,—organic and inorganic. The original significance of these terms was entirely different from the meaning which they have at the present time.

1. Original significance. The division into organic and inorganic was originally made because it was believed that those substances which constitute the essential parts of living organisms were built up under the influence of the life force of the organism. Such substances, therefore, should be regarded as different from those compounds prepared in the laboratory or formed from the inorganic or mineral constituents of the earth. In accordance with this view organic chemistry included those substances formed by living organisms. Inorganic chemistry, on the other hand, included all substances formed from the mineral portions of the earth.

In 1828 the German chemist WÖhler prepared urea, a typical organic compound, from inorganic materials. The synthesis of other so-called organic compounds followed, and at present it is known that the same chemical laws apply to all substances whether formed in the living organism or prepared in the laboratory from inorganic constituents. The terms "organic" and "inorganic" have therefore lost their original significance.

2. Present significance. The great majority of the compounds found in living organisms contain carbon, and the term "organic chemistry," as used at present, includes not only these compounds but all compounds of carbon. Organic chemistry has become, therefore, the chemistry of the compounds of carbon, all other substances being treated under the head of inorganic chemistry. This separation of the compounds of carbon into a group by themselves is made almost necessary by their great number, over one hundred thousand having been recorded. For convenience some of the simpler carbon compounds, such as the oxides and the carbonates, are usually discussed in inorganic chemistry.

The grouping of compounds in classes. The study of organic chemistry is much simplified by the fact that the large number of bodies included in this field may be grouped in classes of similar compounds. It thus becomes possible to study the properties of each class as a whole, in much the same way as we study a group of elements. The most important of these classes are the hydrocarbons, the alcohols, the aldehydes, the acids, the ethereal salts, the ethers, the ketones, the organic bases, and the carbohydrates. A few members of each of these classes will now be discussed briefly.

THE HYDROCARBONS

Carbon and hydrogen combine to form a large number of compounds. These compounds are known collectively as the hydrocarbons. They may be divided into a number of groups or series, each being named from its first member. Some of the groups are as follows:

Only the lower members (that is, those which contain a small number of carbon atoms) of the above groups are given. The methane series is the most extensive, all of the compounds up to C₂₄H₅₀ being known.

It will be noticed that the successive members of each of the above series differ by the group of atoms (CH₂). Such a series is called an homologous series. In general, it may be stated that the members of an homologous series show a regular gradation in most physical properties and are similar in chemical properties. Thus in the methane group the first four members are gases at ordinary temperatures; those containing from five to sixteen carbon atoms are liquids, the boiling points of which increase with the number of carbon atoms present. Those containing more than sixteen carbon atoms are solids.

Sources of the hydrocarbons. There are two chief sources of the hydrocarbons, namely, (1) crude petroleum and (2) coal tar.

1. Crude petroleum. This is a liquid pumped from wells driven into the earth in certain localities. Pennsylvania, Ohio, Kansas, California, and Texas are the chief oil-producing regions in the United States. The crude petroleum consists largely of liquid hydrocarbons in which are dissolved both gaseous and solid hydrocarbons. Before being used it must be refined. In this process the petroleum is run into large iron stills and subjected to fractional distillation. The various hydrocarbons distill over in the general order of their boiling points. The distillates which collect between certain limits of temperature are kept separate and serve for different uses; they are further purified, generally by washing with sulphuric acid, then with an alkali, and finally with water. Among the products obtained from crude petroleum in this way are the naphthas, including benzine and gasoline, kerosene or coal oil, lubricating oils, vaseline, and paraffin. None of these products are definite chemical compounds, but each consists of a mixture of hydrocarbons, the boiling points of which lie within certain limits.

2. Coal tar. This product is obtained in the manufacture of coal gas, as already explained. It is a complex mixture and is refined by the same general method used in refining crude petroleum. The principal hydrocarbons obtained from the coal tar are benzene, toluene, naphthalene, and anthracene. In addition to the hydrocarbons, coal tar contains many other compounds, such as carbolic acid and aniline.

Properties of the hydrocarbons. The lower members of the first two series of hydrocarbons mentioned are all gases; the succeeding members are liquids. In some series, as the methane series, the higher members are solids. The preparation and properties of methane and acetylene have been discussed in a previous chapter. Ethylene is present in small quantities in coal gas and may be obtained in the laboratory by treating alcohol (C₂H₆O) with sulphuric acid:

Benzene, the first member of the benzene series, is a liquid boiling at 80°.

The hydrocarbons serve as the materials from which a large number of compounds can be prepared; indeed, it has been proposed to call organic chemistry the chemistry of the hydrocarbon derivatives.

Substitution products of the hydrocarbons. As a rule, at least a part of the hydrogen in any hydrocarbon can be displaced by an equivalent amount of certain elements or groups of elements. Thus the compounds CH₃Cl, CH₂Cl₂, CHCl₃, CCl₄ can be obtained from methane by treatment with chlorine. Such compounds are called substitution products.

Chloroform (CHCl₃). This can be made by treating methane with chlorine, as just indicated, although a much easier method consists in treating alcohol or acetone (which see) with bleaching powder. Chloroform is a heavy liquid having a pleasant odor and a sweetish taste. It is largely used as a solvent and as an anÆsthetic in surgery.

Iodoform (CHI₃). This is a yellow crystalline solid obtained by treating alcohol with iodine and an alkali. It has a characteristic odor and is used as an antiseptic.

ALCOHOLS

When such a compound as CH₃Cl is treated with silver hydroxide the reaction expressed by the following equation takes place:

Similarly C₂H₅Cl will give C₂H₅OH and AgCl. The compounds CH₃OH and C₂H₅OH so obtained belong to the class of substances known as alcohols. From their formulas it will be seen that they may be regarded as derived from hydrocarbons by substituting the hydroxyl group (OH) for hydrogen. Thus the alcohol CH₃OH may be regarded as derived from methane (CH₄) by substituting the group OH for one atom of hydrogen. A great many alcohols are known, and, like the hydrocarbons, they may be grouped into series. The relation between the first three members of the methane series and the corresponding alcohols is shown in the following table:

Methyl alcohol (wood alcohol) (CH₃OH). When wood is placed in an air-tight retort and heated, a number of compounds are evolved, the most important of which are the three liquids, methyl alcohol, acetic acid, and acetone. Methyl alcohol is obtained entirely from this source, and on this account is commonly called wood alcohol. It is a colorless liquid which has a density of 0.79 and boils at 67°. It burns with an almost colorless flame and is sometimes used for heating purposes, in place of the more expensive ethyl alcohol. It is a good solvent for organic substances and is used especially as a solvent in the manufacture of varnishes. It is very poisonous.

Ethyl alcohol (common alcohol) (C₂H₅OH). 1. Preparation. This compound may be prepared from glucose (C₆H₁₂O₆), a sugar easily obtained from starch. If some baker's yeast is added to a solution of glucose and the temperature is maintained at about 30°, bubbles of gas are soon evolved, showing that a change is taking place. The yeast contains a large number of minute organized bodies, which are really forms of plant life. The plant grows in the glucose solution, and in so doing secretes a substance known as zymase, which breaks down the glucose in accordance with the following equation:

2. Properties. Ethyl alcohol is a colorless liquid with a pleasant odor. It has a density of 0.78 and boils at 78°. It resembles methyl alcohol in its general properties. It is sometimes used as a source of heat, since its flame is very hot and does not deposit carbon, as the flame from oil does. When taken into the system in small quantities it causes intoxication; in larger quantities it acts as a poison. The intoxicating properties of such liquors as beer, wine, and whisky are due to the alcohol present. Beer contains from 2 to 5% of alcohol, wine from 5 to 20%, and whisky about 50%. The ordinary alcohol of the druggist contains 94% of alcohol and 6% of water. When this is boiled with lime and then distilled nearly all the water is removed, the distillate being called absolute alcohol.

Glycerin (C₃H₅(OH)₃). This compound may be regarded as derived from propane (C₃H₈) by displacing three atoms of hydrogen by three hydroxyl groups, and must therefore be regarded as an alcohol. It is formed in the manufacture of soaps, as will be explained later. It is an oily, colorless liquid having a sweetish taste. It is used in medicine and in the manufacture of the explosives nitroglycerin and dynamite.

ALDEHYDES

When alcohols are treated with certain oxidizing agents two hydrogen atoms are removed from each molecule of the alcohol. The resulting compounds are known as aldehydes. The relation of the aldehydes derived from methyl and ethyl alcohol to the alcohols themselves may be shown as follows:

The first of these (CH₂O) is a gas known as formaldehyde. Its aqueous solution is largely used as an antiseptic and disinfectant under the name of formalin. Acetaldehyde (C₂H₄O) is a liquid boiling at 21°.

ACIDS

Like the other classes of organic compounds, the organic acids may be arranged in homologous series. One of the most important of these series is the fatty-acid series, the name having been given to it because the derivatives of certain of its members are constituents of the fats. Some of the most important members of the series are given in the following table. They are all monobasic, and this fact is expressed in the formulas by separating the replaceable hydrogen atom from the rest of the molecule:

Formic acid (H·CHO₂). The name "formic" is derived from the Latin formica, signifying ant. This name was given to the acid because it was formerly obtained from a certain kind of ants. It is a colorless liquid and occurs in many plants such as the stinging nettles. The inflammation caused by the sting of the bee is due to formic acid.

Acetic acid (H·C₂H₃O₂). Acetic acid is the acid present in vinegar, the sour taste being due to it. It can be prepared by either of the following methods.

1. Acetic fermentation. This consists in the change of alcohol into acetic acid through the agency of a minute organism commonly called mother of vinegar. The change is represented by the following equation:

The various kinds of vinegars are all made by this process. In the manufacture of cider vinegar the sugar present in the cider first undergoes alcoholic fermentation; the resulting alcohol then undergoes acetic fermentation. The amount of acetic acid present in vinegars varies from 3 to 6%.

2. From the distillation of wood. The liquid obtained by heating wood in the absence of air contains a large amount of acetic acid, and this can be separated readily in a pure state. This is the most economical method for the preparation of the concentrated acid.

Acetic acid is a colorless liquid and has a strong pungent odor. Many of its salts are well-known compounds. Lead acetate (Pb(C₂H₃O₂)₂) is the ordinary sugar of lead. Sodium acetate (NaC₂H₃O₂) is a white solid largely used in making chemical analyses. Copper acetate (Cu(C₂H₃O₂)₂) is a blue solid. When copper is acted upon by acetic acid in the presence of air a green basic acetate of copper is formed. This is commonly known as verdigris. All acetates are soluble in water.

Butyric acid (H·C₄H₇O₂). Derivatives of butyric acid are present in butter and impart to it its characteristic flavor.

Palmitic and stearic acids. Ordinary fats consist principally of derivatives of palmitic and stearic acids. When the fats are heated with sodium hydroxide the sodium salts of these acids are formed. If hydrochloric acid is added to a solution of the sodium salts, the free palmitic and stearic acids are precipitated. They are white solids, insoluble in water. Stearic acid is often used in making candles.

Acids belonging to other series. In addition to members of the fatty-acid series, mention may be made of the following well-known acids.

Oxalic acid (H₂C₂O₄). This is a white solid which occurs in nature in many plants, such as the sorrels. Its ammonium salt ((NH₄)₂C₂O₄) is used as a reagent for the detection of calcium. When added to a solution of a calcium compound the white, insoluble calcium oxalate (CaC₂O₄) precipitates.

Tartaric acid (H₂·C₄H₄O₆). This compound occurs either in a free state or in the form of its salts in many fruits. The potassium acid salt (KHC₄H₄O₆) occurs in the juice of grapes. When the juice ferments in the manufacture of wine, this salt, being insoluble in alcohol, separates out on the sides of the cask and in this form is known as argol. This is more or less colored by the coloring matter of the grape. When purified it forms a white solid and is sold under the name of cream of tartar. The following are also well-known salts of tartaric acid: potassium sodium tartrate (Rochelle salt) (KNaC₄H₄O₆), potassium antimonyl tartrate (tartar emetic) (KSbOC₄H₄O₆).

Citric acid (H₃·C₆H₅O₇). This acid occurs in many fruits, especially in lemons. It is a white solid, soluble in water, and is often used as a substitute for lemons in making lemonade.

Lactic acid (H·C₃H₅O₃). This is a liquid which is formed in the souring of milk.

Oleic acid (H·C₁₈H₃₃O₂). The derivatives of this acid constitute the principal part of many oils and liquid fats. The acid itself is an oily liquid.

ETHEREAL SALTS

When acids are brought in contact with alcohols under certain conditions a reaction takes place similar to that which takes place between acids and bases. The following equations will serve as illustrations:

The resulting compounds of which methyl nitrate (CH₃NO₃) may be taken as the type belong to the class known as ethereal salts, the name having been given them because some of them possess pleasant ethereal odors. It will be seen that the ethereal salts differ from ordinary salts in that they contain a hydrocarbon radical, such as CH₃, C₂H₅, C₃H₅, in place of a metal.

The nitrates of glycerin (nitroglycerin). Nitric acid reacts with glycerin in the same way that it reacts with a base containing three hydroxyl groups such as Fe(OH)₃:

The resulting nitrate (C₃H₅(NO₃)₃) is the main constituent of nitroglycerin, a slightly yellowish oil characterized by its explosive properties. Dynamite consists of porous earth which has absorbed nitroglycerin, and its strength depends on the amount present. It is used much more largely than nitroglycerin itself, since it does not explode so readily by concussion and hence can be transported with safety.

The fats. These are largely mixtures of the ethereal salts known respectively as olein, palmitin, and stearin. These salts may be regarded as derived from oleic, palmitic, and stearic acids respectively, by replacing the hydrogen of the acid with the glycerin radical C₃H₅. Since this radical is trivalent and oleic, palmitic, and stearic acids contain only one replaceable hydrogen atom to the molecule, it is evident that three molecules of each acid must enter into each molecule of the ethereal salt. The formulas for the acids and the ethereal salts derived from each are as follows:

Olein is a liquid and is the main constituent of liquid fats. Palmitin and stearin are solids.

Butter fat and oleomargarine. Butter fat consists principally of olein, palmitin, and stearin. The flavor of the fat is due to the presence of a small amount of butyrin, which is an ethereal salt of butyric acid. Oleomargarine differs from butter mainly in the fact that a smaller amount of butyrin is present. It is made from the fats obtained from cattle and hogs. This fat is churned up with milk, or a small amount of butter is added, in order to furnish sufficient butyrin to impart the butter flavor.

Saponification. When an ethereal salt is heated with an alkali a reaction expressed by the following equation takes place:

This process is known as saponification, since it is the one which takes place in the manufacture of soaps. The ordinary soaps are made by heating fats with a solution of sodium hydroxide. The reactions involved may be illustrated by the following equation representing the reaction between palmitin and sodium hydroxide:

In accordance with this equation the ethereal salts in the fats are converted into glycerin and the sodium salts of the corresponding acids. The sodium salts are separated and constitute the soaps. These salts are soluble in water. When added to water containing calcium salts the insoluble calcium palmitate and stearate are precipitated. Magnesium salts act in a similar way. It is because of these facts that soap is used up by hard waters.

ETHERS

When ethyl alcohol is heated to 140° with sulphuric acid the reaction expressed by the following equation takes place:

The resulting compound, (C₂H₅)₂O, is ordinary ether and is the most important member of the class of compounds called ethers. Ordinarily ether is a light, very inflammable liquid boiling at 35°. It is used as a solvent for organic substances and as an anÆsthetic in surgical operations.

KETONES

The most common member of this group is acetone (C₃H₆O), a colorless liquid obtained when wood is heated in the absence of air. It is used in the preparation of other organic compounds, especially chloroform.

ORGANIC BASES

This group includes a number of compounds, all of which contain nitrogen as well as carbon. They are characterized by combining directly with acids to form salts, and in this respect they resemble ammonia. They may, indeed, be regarded as derived from ammonia by displacing a part or all of the hydrogen present in ammonia by hydrocarbon radicals. Among the simplest of these compounds may be mentioned methylamine (CH₃NH₂) and ethylamine (C₂H₅NH₂). These two compounds are gases and are formed in the distillation of wood and bones. Pyridine (C₅H₆N) and quinoline (C₉H₇N) are liquids present in small amounts in coal tar, and also in the liquid obtained by the distillation of bones. Most of the compounds now classified under the general name of alkaloids (which see) also belong to this group.

CARBOHYDRATES

The term "carbohydrate" is applied to a class of compounds which includes the sugars, starch, and allied bodies These compounds contain carbon, hydrogen, and oxygen the last two elements generally being present in the proportion in which they combine to form water. The most important members of this class are the following:

Cane sugar (C₁₂H₂₂O₁₁). This is the well-known substance commonly called sugar. It occurs in many plants especially in the sugar cane and sugar beet. It was formerly obtained almost entirely from the sugar cane, but at present the greatest amount of it comes from the sugar beet. The juice from the cane or beet contains the sugar in solution along with many impurities. These impurities are removed, and the resulting solution is then evaporated until the sugar crystallizes out. The evaporation is conducted in closed vessels from which the air is partially exhausted. In this way the boiling point of the solution is lowered and the charring of the sugar is prevented. It is impossible to remove all the sugar from the solution. In preparing sugar from sugar cane the liquors left after separating as much of it as possible from the juice of the cane constitute ordinary molasses. Maple sugar is made by the evaporation of the sap obtained from a species of the maple tree. Its sweetness is due to the presence of cane sugar, other products present in the maple sap imparting the distinctive flavor.

When a solution of cane sugar is heated with hydrochloric or other dilute mineral acid, two compounds, dextrose and levulose, are formed in accordance with the following equation:

This same change is brought about by the action of an enzyme present in the yeast plant. When yeast is added to a solution of cane sugar fermentation is set up. The cane sugar, however, does not ferment directly: the enzyme in the yeast first transforms the sugar into dextrose and levulose, and these sugars then undergo alcoholic fermentation.

When heated to 160° cane sugar melts; if the temperature is increased to about 215°, a partial decomposition takes place and a brown substance known as caramel forms. This is used largely as a coloring matter.

Milk sugar (C₁₂H₂₂O₁₁). This sugar is present in the milk of all mammals. The average composition of cow's milk is as follows:

When rennin, an enzyme obtained from the stomach of calves, is added to milk, the casein separates and is used in the manufacture of cheese. The remaining liquid contains the milk sugar which separates on evaporation; it resembles cane sugar in appearance but is not so sweet or soluble. The souring of milk is due to the fact that the milk sugar present undergoes lactic fermentation in accordance with the equation

The lactic acid formed causes the separation of the casein, thus giving the well-known appearance of sour milk.

Isomeric compounds. It will be observed that cane sugar and milk sugar have the same formulas. Their difference in properties is due to the different arrangement of the atoms in the molecule. Such compounds are said to be isomeric. Dextrose and levulose are also isomeric.

Dextrose (grape sugar, glucose) (C₆H₁₂O₆). This sugar is present in many fruits and is commonly called grape sugar because of its presence in grape juice. It can be obtained by heating cane sugar with dilute acids, as explained above; also by heating starch with dilute acids, the change being as follows:

Pure dextrose is a white crystalline solid, readily soluble in water, and is not so sweet as cane sugar. In the presence of yeast it undergoes alcoholic fermentation. It is prepared from starch in large quantities, and being less expensive than cane sugar, is used as a substitute for it in the manufacture of jellies, jams, molasses, candy, and other sweets. The product commonly sold under the name of glucose contains about 45% of dextrose.

Levulose (fruit sugar)(C₆H₁₂O₆). This sugar is a white solid which occurs along with dextrose in fruits and honey. It undergoes alcoholic fermentation in the presence of yeast.

Cellulose (C₆H₁₀O₅). This forms the basis of all woody fibers. Cotton and linen are nearly pure cellulose. It is insoluble in water, alcohol, and dilute acids. Sulphuric acid slowly converts it into dextrose. Nitric acid forms nitrates similar to nitroglycerin in composition and explosive properties. These nitrates are variously known as nitrocellulose, pyroxylin, and gun cotton. When exploded they yield only colorless gases; hence they are used especially in the manufacture of smokeless gunpowder. Collodion is a solution of nitrocellulose in a mixture of alcohol and ether. Celluloid is a mixture of nitrocellulose and camphor. Paper consists mainly of cellulose, the finer grades being made from linen and cotton rags, and the cheaper grades from straw and wood.

Starch (C₆H₁₀O₅). This is by far the most abundant carbohydrate found in nature, being present especially in seeds and tubers. In the United States it is obtained chiefly from corn, nearly 80% of which is starch. In Europe it is obtained principally from the potato. It consists of minute granules and is practically insoluble in cold water. These granules differ somewhat in appearance, according to the source of the starch, so that it is often possible to determine from what plant the starch was obtained. When heated with water the granules burst and the starch partially dissolves. Dilute acids, as well as certain enzymes, convert it into dextrose or similar sugars. When seeds germinate the starch present is converted into soluble sugars, which are used as food for the growing plant.

Chemical changes in bread making. The average composition of wheat flour is as follows:

In making bread the flour is mixed with water and yeast, and the resulting dough set aside in a warm place for a few hours. The yeast first converts a portion of the starch into dextrose or a similar sugar, which then undergoes alcoholic fermentation. The carbon dioxide formed escapes through the dough, making it light and porous. The yeast plant thrives best at about 30°; hence the necessity for having the dough in a warm place. If the temperature rises above 50°, the vitality of the yeast is destroyed and fermentation ceases. In baking the bread, the heat expels the alcohol and also expands the bubbles of carbon dioxide caught in the dough, thus increasing its lightness.

SOME DERIVATIVES OF BENZENE

Attention has been called to the complex nature of coal tar. Among the compounds present are the hydrocarbons, benzene, toluene, naphthalene, and anthracene. These compounds are not only useful in themselves but serve for the preparation of many other important compounds known under the general name of coal-tar products.

Nitrobenzene (oil of myrbane) (C₆H₅NO₂). When benzene is treated with nitric acid a reaction takes place which is expressed by the following equation:

The product C₆H₅NO₂ is called nitrobenzene. It is a slightly yellowish poisonous liquid, with a characteristic odor. Its main use is in the manufacture of aniline.

Aniline (C₆H₅NH₂). When nitrobenzene is heated with iron and hydrochloric acid the hydrogen evolved by the action of the iron upon the acid reduces the nitrobenzene in accordance with the following equation:

The resulting compound is known as aniline, a liquid boiling at 182°. When first prepared it is colorless, but darkens on standing. Large quantities of it are used in the manufacture of the aniline or coal-tar dyes, which include many important compounds.

Carbolic acid (C₆H₅OH). This compound, sometimes known as phenol, occurs in coal tar, and is also prepared from benzene. It forms colorless crystals which are very soluble in water. It is strongly corrosive and very poisonous.

Naphthalene and anthracene. These are hydrocarbons occurring along with benzene in coal tar. They are white solids, insoluble in water. The well-known moth balls are made of naphthalene. Large quantities of naphthalene are used in the preparation of indigo, a dye formerly obtained from the indigo plant, but now largely prepared by laboratory methods. Similarly anthracene is used in the preparation of the dye alizarin, which was formerly obtained from the madder root.

THE ALKALOIDS

This term is applied to a group of compounds found in many plants and trees. They all contain nitrogen, and most of them are characterized by their power to combine with acids to form salts. This property is indicated by the name alkaloids, which signifies alkali-like. The salts are soluble in water, and on this account are more largely used than the free alkaloids, which are insoluble in water. Many of the alkaloids are used in medicine, some of the more important ones being given below.

Quinine. This alkaloid occurs along with a number of others in the bark of certain trees which grow in districts in South America and also in Java and other tropical islands. It is a white solid, and its sulphate is used in medicine in the treatment of fevers.

Morphine. When incisions are made in the unripe capsules of one of the varieties of the poppy plant, a milky juice exudes which soon thickens. This is removed and partially dried. The resulting substance is the ordinary opium which contains a number of alkaloids, the principal one being morphine. This alkaloid is a white solid and is of great service in medicine.

Among the other alkaloids may be mentioned the following: Nicotine, a very poisonous liquid, the salts of which occur in the leaves of the tobacco plant; cocaine, a crystalline solid present in coca leaves and used in medicine as a local anÆsthetic; atropine, a solid present in the berry of the deadly nightshade, and used in the treatment of diseases of the eye; strychnine, a white, intensely poisonous solid present in the seeds of the members of the Strychnos family.