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
[Sidenote: 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.
[Sidenote: 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
[Sidenote: 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).
[Sidenote: 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
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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
[Sidenote: 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.
[Sidenote: 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
[Sidenote: 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).
[Sidenote: 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.
[Sidenote: 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.
[Sidenote: 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.