11 March 2010

Refrigerant gas

The invention: A safe refrigerant gas for domestic refrigerators,
dichlorodifluoromethane helped promote a rapid growth in the
acceptance of electrical refrigerators in homes.
The people behind the invention:
Thomas Midgley, Jr. (1889-1944), an American engineer and
Charles F. Kettering (1876-1958), an American engineer and
inventor who was the head of research for General Motors
Albert Henne (1901-1967), an American chemist who was
Midgley’s chief assistant
Frédéric Swarts (1866-1940), a Belgian chemist
Toxic Gases
Refrigerators, freezers, and air conditioners have had a major impact
on the way people live and work in the twentieth century.With
them, people can live more comfortably in hot and humid areas,
and a great variety of perishable foods can be transported and
stored for extended periods. As recently as the early nineteenth century,
the foods most regularly available to Americans were bread
and salted meats. Items now considered essential to a balanced diet,
such as vegetables, fruits, and dairy products, were produced and
consumed only in small amounts.

Through the early part of the twentieth century, the pattern of
food storage and distribution evolved to make perishable foods
more available. Farmers shipped dairy products and frozen meats
to mechanically refrigerated warehouses. Smaller stores and most
American households used iceboxes to keep perishable foods fresh.
The iceman was a familiar figure on the streets of American towns,
delivering large blocks of ice regularly.
In 1930, domestic mechanical refrigerators were being produced
in increasing numbers. Most of them were vapor compression machines,
in which a gas was compressed in a closed system of pipes
outside the refrigerator by a mechanical pump and condensed to a liquid. The liquid was pumped into a sealed chamber in the refrigerator
and allowed to evaporate to a gas. The process of evaporation
removes heat from the environment, thus cooling the interior of the
The major drawback of early home refrigerators involved the
types of gases used. In 1930, these included ammonia, sulfur dioxide,
and methyl chloride. These gases were acceptable if the refrigerator’s
gas pipes never sprang a leak. Unfortunately, leaks sometimes
occurred, and all these gases are toxic. Ammonia and sulfur
dioxide both have unpleasant odors; if they leaked, at least they
would be detected rapidly. Methyl chloride however, can form a
dangerously explosive mixture with air, and it has only a very faint,
and not unpleasant, odor. In a hospital in Cleveland during the
1920’s, a refrigerator with methyl chloride leaked, and there was a
disastrous explosion of the methyl chloride-air mixture. After that,
methyl chloride for use in refrigerators was mixed with a small
amount of a very bad-smelling compound to make leaks detectable.
(The same tactic is used with natural gas.)
Three-Day Success
General Motors, through its Frigidaire division, had a substantial
interest in the domestic refrigerator market. Frigidaire refrigerators
used sulfur dioxide as the refrigerant gas. Charles F. Kettering,
director of research for General Motors, decided that Frigidaire
needed a new refrigerant gas that would have good thermal properties
but would be nontoxic and nonexplosive. In early 1930, he sent
Lester S. Keilholtz, chief engineer of General Motors’ Frigidaire division,
to Thomas Midgley, Jr., a mechanical engineer and selftaught
chemist. He challenged them to develop such a new gas.
Midgley’s associates, Albert Henne and Robert McNary, researched
what types of compounds might already fit Kettering’s specifications.
Working with research that had been done by the Belgian
chemist Frédéric Swarts in the late nineteenth and early twentieth
centuries, Midgley, Henne, and McNary realized that dichlorodifluoromethane
would have ideal thermal properties and the right
boiling point for a refrigerant gas. The only question left to be answered
was whether the compound was toxic.
The chemists prepared a few grams of dichlorodifluoromethane
and put it, along with a guinea pig, into a closed chamber. They
were delighted to see that the animal seemed to suffer no ill effects
at all and was able to breathe and move normally. They were briefly
puzzled when a second batch of the compound killed a guinea pig
almost instantly. Soon, they discovered that an impurity in one of
the ingredients had produced a potent poison in their refrigerant
gas. A simple washing procedure completely removed the poisonous
This astonishingly successful research project was completed in
three days. The boiling point of dichlorodifluoromethane is -5.6 degrees
Celsius. It is nontoxic and nonflammable and possesses excellent
thermal properties. When Midgley was awarded the Perkin
Medal for industrial chemistry in 1937, he gave the audience a
graphic demonstration of the properties of dichlorodifluoromethane:
He inhaled deeply of its vapors and exhaled gently into a jar
containing a burning candle. The candle flame promptly went out.
This visual evidence proved that dichlorodifluoromethane was not
poisonous and would not burn.
The availability of this safe refrigerant gas, which was renamed
Freon, led to drastic changes in the United States. The current patterns
of food production, distribution, and consumption are a direct
result, as is air conditioning. Air conditioning was developed early
in the twentieth century; by the late 1970’s, most American cars and
residences were equipped with air conditioning, and other countries
with hot climates followed suit. Consequently, major relocations
of populations and businesses have become possible. Since
World War II, there have been steady migrations to the “Sun Belt,”
the states spanning the United States from southeast to southwest,
because air conditioners have made these areas much more livable.
Freon is a member of a family of chemicals called “chlorofluorocarbons.”
In addition to refrigeration, it is also used as a propellant
in aerosols and in the production of polystyrene plastics. In 1974,
scientists began to suspect that chlorofluorocarbons, when released
into the air, might have a serious effect on the environment. They
speculated that the compounds might migrate into the stratosphere,
where they could be decomposed by the intense ultraviolet light
from the sunlight that is prevented from reaching the earth’s surface
by the thin but vital layer of ozone in the stratosphere. In the process,
large amounts of the ozone layer might also be destroyed—
letting in the dangerous ultraviolet light. In addition to possible climatic
effects, the resulting increase in ultraviolet light reaching the
earth’s surface would raise the incidence of skin cancers. As a result,
chemical manufacturers are trying to develop alternative refrigerant
gases that will not harm the ozone layer.


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