Volume 5 — LESSON III
Reading edition
ORGANIC CHEMISTRY
CARBON
In this lesson I will consider carbon and carbon compounds, which are the bases of all foods and living matter. I will devote but little attention to theories and technicalities, but will discuss the subject from scientific and practical standpoints.
Wood, flesh, and other products of vegetable or of animal life blacken when heated to a sufficiently high temperature. This blackening is due to the presence of carbon. If such substances are heated with an abundant supply of air, the carbon combines with oxygen and forms a colorless gas; that is, the carbon burns.
Sources of carbon
The principal form in which carbon occurs in nature is in combination with other elements. It occurs not only in all living things, but in their fossil remains, as in coal. All products of plant life contain carbon, hydrogen, and oxygen. Among the more common of these are sugar, starch, wood, etc. Most products of animal life contain carbon, hydrogen, oxygen, and nitrogen. Among these are albumin, fibrin, casein, etc.
Carbon occurs in the atmosphere in the form of carbon dioxid or carbonic acid gas. It is also found in the earth in the form of salts of carbonic acid or carbonates, such as limestone, marble, and chalk.
Various forms of carbon
The pure element, carbon, is found in nature in the form of diamonds, which are pure crystallized carbon. Small diamonds are now made artificially in electric furnaces. Crystallized carbon also occurs in nature in the form of graphite, from which lead pencils are made. Charcoal, lampblack, and coke are forms of amorphous carbon which contain a very small percentage of impurities.
Properties of carbon
Notwithstanding the marked difference in their appearance, the various forms of carbon have some properties in common. They are insoluble in all known liquids. They are tasteless, odorless, and infusible at ordinary temperature. When heated without access of air, they remain unchanged unless the temperature is very high, in which case they unite with oxygen and are consumed, forming carbon dioxid.
INORGANIC CARBON COMPOUNDS
CARBON DIOXID (CO2)
The principal compound of carbon and oxygen is carbon dioxid, often called carbonic acid gas. This gas is always present in the air. It issues from the earth in many places, particularly in the neighborhood of volcanoes. With it many mineral waters are naturally charged.
How carbon dioxid enters the air
Carbon dioxid is constantly formed by many natural processes. Every animal that breathes gives off carbon dioxid from its lungs. This gas is also formed whenever ordinary combustible materials are burned. The natural processes of decay of both vegetable and animal matter tend to convert the carbon contained therein into carbon dioxid, which is thrown off and absorbed into the air. The process of alcoholic fermentation, and similar processes, also give rise to the formation of this gas. When fruits ripen, fall, and decay, the sugar, which all fruit-juices contain, is changed to alcohol and carbon dioxid.
RELATION OF CARBON DIOXID TO LIFE
Action of plants upon carbon dioxid
Carbon dioxid is an important factor in the life activity of the earth. The leaves of plants absorb carbon dioxid from the air, and by means of the chemical activity of the green coloring-matter or chlorophyl, the plant has the power of combining the carbon dioxid with water, and with the mineral salts which have been absorbed from the earth by the roots of the plant. Sunlight is necessary to this action, especially in the manufacture of starch.
This formation of food material in plants by the combination of simple chemical substances, such as carbon dioxid and water, is one of the fundamental life-processes. Animals do not possess this power of utilizing simple or inorganic chemical compounds, therefore they must take their food substances in the more complex forms which have been created by the power of sunlight acting upon the plant.
The wonderful carbon cycle
I have already explained how carbon dioxid may enter the air. Thus we see that the carbon dioxid which is withdrawn from the air, by the growth of plants, is constantly replaced by combustion, and in this way the "carbon cycle" is completed. This is one of the most beautiful adaptations in nature. If the plant did not remove the carbon dioxid from the air, it would soon accumulate in such quantities as to become detrimental to life, and, on the other hand, if this gas were not returned to the air by combustion, by the breathing of animals, and by the decay of plants, the vegetable world would soon be without carbon dioxid, which is as essential to plant life as is the oxygen of the air to animal life.
CARBON MONOXID (CO)
This compound is formed when a substance containing carbon is burned in an insufficient supply of air, as for example when the draught is partly shut off in a stove.
Properties of carbon monoxid
Carbon monoxid is a colorless gas. It burns with a blue flame, forming carbon dioxid. The blue flame seen playing over the embers of a coal fire is carbon monoxid burning. This gas is extremely poisonous. Carbon dioxid, CO2, is not poisonous. The poisonous properties of illuminating gas are due to the carbon monoxid which it contains.
ORGANIC CARBON COMPOUNDS
The carbon compounds thus far considered have been mentioned to illustrate a few of the simpler or inorganic forms of carbon. We will now begin the study of organic chemistry or the compounds of carbon which are commonly found only in plant and animal substances.
Combining power of carbon
Carbon has wonderful powers of combination with other chemical elements, and may combine with the same elements in thousands of different proportions. This property of carbon to form so many different compounds is considered one of the fundamental facts of chemistry upon which life depends. For example:
Carbon and hydrogen compounds
Oxygen can combine with hydrogen in but two proportions—peroxid of hydrogen (H2O2) and water (H2O)—while carbon and hydrogen can combine in more than a hundred different compounds. The simpler of these are acetylene (C2H2) and marsh gas or methane (CH4), which is the fire-damp in mines.
The compounds containing carbon, hydrogen, and oxygen number into the thousands. A great many substances formed in plants contain these three elements, such as fruit-acids, alcohol, sugar, and fats.
CLASSIFICATION OF ORGANIC CARBON COMPOUNDS
Only a few of the most important groups of the organic or life-formed carbon compounds will be considered in this work, namely:
a Hydrocarbons
b Alcohols
c Glycerin
d Aldehydes and ethers
e Organic acids
f Carbohydrates
g Fats
a HYDROCARBONS
Uses of hydrocarbons in industrial chemistry
Hydrocarbons are compounds of the two elements carbon and hydrogen. These compounds are very important in industrial chemistry. They are found in petroleum, coal-tar, etc., which were originally formed from decaying and petrifying masses of plants. Gasoline, benzin, naphtha, acetylene, methane, etc., are some of the industrial forms by which hydrocarbons are known in commerce.
Coal-tar products
The industries based upon the chemistry of these hydrocarbons are very complex and interesting. Coal-tar yields, by repeated distillation and chemical reaction, thousands of compounds, many of which find important industrial usages. Coal-tar dyes are very numerous and of wonderful coloring power. They have been extensively used in the artificial coloring of manufactured foods. The Federal Pure Food Law attempted to prohibit this. In fact, it was the pernicious effect and extensive use of these poisons that stimulated the passage of the "Food and Drugs Act." Another interesting product of the coal-tar industry is saccharin. Saccharin has no food value whatever, but it is 280 times sweeter than cane-sugar, and is therefore used as a substitute in sweetening some prepared foods.
b ALCOHOLS
Varieties of alcohol
To the ordinary mind the term alcohol refers only to the intoxicating element in liquors. To the chemist, alcohol has a much broader significance. There are many varieties of alcohols, of which ethyl alcohol (C2H5.HO), which is found in liquors, is only one example. Another form of alcohol which is fairly well known is wood or methyl alcohol (CH3.OH).
Formation of higher alcohols
There are also higher alcohols, that is, those having more complex chemical formulas, such as butyl alcohol. In the fermentation of grains or fruits for intoxicating liquors, a small quantity of the various higher alcohols is formed. These higher alcohols are more intoxicating and more harmful to the human system than ethyl alcohol, and must be separated from the latter by careful distillation. The poisonous property of green whisky and cheap liquors is generally due to the presence of higher alcohols.
Alcohol does not exist in normal, fresh plant or animal substances except in very minute quantities. It is formed from sugar by fermentation. This fermentation is due to a microscopic yeast-plant.
c GLYCERIN
Another form of alcohol is glycerin (C3H8O3). It is of special interest to the food chemist because it enters into the formation of all fats.
d ALDEHYDES AND ETHERS
How formed
These are compounds containing carbon, hydrogen, and oxygen, and are closely related to alcohols. In fact they are formed from alcohols by a process of oxidation, hence contain a little larger proportion of oxygen than the related alcohol.
Uses of formaldehyde
An example of aldehyde with which many are familiar is formaldehyde, which is used in laboratories for the preservation of animal-tissues for dissection. This formaldehyde is a very strong germicide; that is, it is poisonous to bacteria or germs. For this reason it is used as a preservative of milk, a use which is forbidden by the "Food and Drugs Act," because formaldehyde is also poisonous to the human system.
Uses of ether
Ethyl ether, which is used as an anesthetic or to produce insensibility to pain, will serve as an illustration of this group of compounds. When analyzing foods in chemical laboratories, ether is commonly used for dissolving fats.
e ORGANIC ACIDS
Properties of organic acids
It will be remembered that acids were studied in the second lesson. It was found that the common properties of acids are a sour taste, ability to combine with alkalis in the formation of salts, and that all acids contain hydrogen. These same properties that were studied in the second lesson in reference to mineral acids, such as hydrochloric and sulfuric, apply also to the organic acids. The organic acids, however, as a class are not so strong or active as the mineral acids.
All organic acids are compounds of carbon, hydrogen, and oxygen, the same as alcohols and ethers, the chief difference between these compounds and acids being that the acids contain a greater proportion of oxygen. One of the simplest organic acids is formic acid (HCO.OH). This acid is the active principle in the sting of the red ant, and also of stinging nettles. It produces blisters when applied to the skin.
Process of making acetic acid
Impure acetic acid (C2H4O2) is very well known to all under the name of vinegar. Acetic acid may be obtained by distilling wood. If it could be manufactured cheaply enough, vinegar made from wood would be fully as wholesome as the best cider vinegars, but this being an expensive process of manufacture, the temptation of the food adulterator is to make the vinegar of sulfuric acid, which is much cheaper than the mild acetic acid, but much more harmful when taken into the body.
The formic and the acetic acids are examples of a series of organic acids known as fatty acids. Other members of the series are—
Propionic acid C3H6O2
Butyric "C4H8O2
Palmitic "C16H32O2
Stearic "C18H36O2
Process of making soap
These fatty acids are very important to the food scientist as they combine with glycerin to form fats. When combined with alkalis under a certain temperature they form soap. Perhaps some of our older students may remember the soap kettle on the farm at home, in which lard cracklings and other fatty fragments of the animal were boiled with lye or caustic potash to form home-made soap. The chemical action that took place was a combination of these fatty acids with the caustic potash or lye. The glycerin was set free and remained in the bottom of the kettle as soft soap. Reference will be made to these acids again, in Lesson IV, where the study of fats will be taken up in detail. (See "Fats and Oils," under Lesson IV, Chemistry of Foods, p. 122).
Oxalic acid
There are some other forms of organic acids which do not belong in the fatty series; that is, they do not contain the same general proportions of carbon and hydrogen. One of these is oxalic acid (C2H2O4) which is found in certain plants, such as sorrel, and is an active poison. Oxalic acid is used in the household for taking iron-rust out of cloth.
Lactic, malic and tartaric acids
Lactic acid (C3H6O3) is the acid of sour milk. Malic acid (C4H6O5) is found in many fruits such as apples, apricots, currants, pears, plums, prunes, etc. Tartaric acid (C4H6O6) is found principally in grapes. It is one of the constituent elements in the sediment found in wine casks, and is the active principle in cream of tartar. The latter is a potassium salt of tartaric acid.
Citric acid
Citric acid (C6H8O7) is one of the most important of the organic acids from the standpoint of the food chemist. It is the active principle of citrus-fruits, such as grapefruit, lemons, limes, oranges, etc. Lemons contain as high as five per cent of this acid. Citric acid is often used to make lemonade, and if pure citric acid is used, the manufactured product is equal to the original, except from a sentimental standpoint of having the genuine. The danger is, as in the case of adulterated vinegar, that the manufacturer may be tempted to use cheaper mineral acids instead of citric acid.
The other above-named groups of organic compounds which are formed from the three elements carbon, hydrogen, and oxygen—(f) carbohydrates and (g) fats—are very important to the food chemist. These will be considered in detail in Lesson IV. See pages 107-125.
ORGANIC NITROGENOUS COMPOUNDS
If to the three elements carbon, hydrogen, and oxygen, the element nitrogen is added, it still further increases the number of possible compounds that may be formed upon the base of the wonderful carbon atom. With this additional nitrogen factor, a new and a distinct quality is obtained.
The elements that make life possible
The chief characteristic of the element nitrogen is the ease with which its compounds change their chemical form. To quote the chemist, "the compounds of nitrogen are very unstable." Nearly all explosives are nitrogenous compounds. When this element, nitrogen, is combined with the wonderful variety of compounds formed by carbon, we have not only a great many intimately related yet distinct substances, but compounds which readily change from one form to another. These are the distinctive qualities or conditions necessary, from a chemical standpoint, to make the processes of life possible. Protoplasm, which is the basis of all life, is formed by an intimate mixture of a number of complex chemical compounds, the chief elements of which are carbon, hydrogen, oxygen, and nitrogen.
Importance of nitrogenous compounds
The organic compounds containing nitrogen are very numerous and very interesting. As all tissues and substances of the animal body contain nitrogen as a necessary element, we can see why this group of compounds is of great importance to the student of food science.
Some of the nitrogenous compounds which are not available as nutritive substances, and many of which are poisonous or harmful to animal life, will be considered in Lesson IX, under "Alkaloids and Narcotics." (See Vol. II, p. 349.) The principal nutritive substances, and proteids or compounds containing available food nitrogen, will be considered in Lesson IV.