An account of tetraethyl lead from an
American Chemistry textbook of 1938. [Chemistry and its Wonders, American Book Co.
1938]
.......Thomas Midgley Jr., the chemist who had this problem to solve, gave
us tetraethyl lead of which we hear a great deal.
Tetraethyl lead is so effective as a knock preventer that it is necessary
to put only four ounces of it into fifty gallons of gasoline to eliminate
knocking completely at pressures much greater than could be used successfully
without it....
The periodic system also has enabled the chemist to find compounds with
certain definite desirable properties. For instance Thomas Midgley Jnr.,
in his search for an anti-knock compound for gasoline was able to predict
that tetraethyl lead would be the best of all the possible compounds before
it had been tried . All his predictions were based on a study of the periodic
arrangement....The antiknock properties of gasoline have been increased by
the addition of tetraethyl lead. Knocking jars the wall of the automobile
cylinders by the explosion instead of steadily pushing the cylinder back.
Knocking represents the wastage of a large percentage of the energy. The wastage
of energy is not the worst thing connected with knocking; it injures the
car.
Engineers calculated that they could design automobile engines with much
greater power and pickup if they could avoid knocking. They planned to get
more power by increasing the compression ratio; in other words, they would
compress the mixture of gasoline vapour and air more before exploding
it. At the time of the development of tetraethyl lead, the compression ratio
commonly used was 4.5 : 1, that is when the piston was entirely back, volume
of gases was 4.5 times the volume than when it was fired by the spark. With
this coming of tetraethyl lead, the compression ratios of practically all
automobile engines were increased to 5.5 to 1 and greater.
It was discovered that iodine would prevent knocking. Iodine however is
very expensive and corrodes the cylinder wall. These factors make it unsuitable
for knock prevention. Having found one substance that prevents knocking,
investigators began to search for other substances which would do the same.
Of all things tried for this purpose, tetraethyl lead, Pb(C2H5)4,
was the most effective. However at the time the antiknock property of tetraethyl
lead was discovered, this substance was just a laboratory curiosity and very
expensive. Intensive research soon developed cheaper ways of preparing the
new knock preventer, and it became a commercial product. Now tetraethyl lead
is added to many of the better grades of gasoline. The antiknock property
of gasoline is rated in terms of the hydrocarbon isooctane, which possesses
high antiknock qualities. A gasoline of rating 80 is a gasoline
of antiknock properties equal to a mixture of 80% isooctane. The power obtained
from gasoline increases rapidly with the octane rating . There is a 20-30%
increase in power of gasoline of octane number 100 over that of octane number
87.
Dichloro-difluoromethane [from the same text, 1938]
Some time ago an electric refrigerating system sprang a leak and and several
people were asphyxiated. The accident emphasises the need of a perfectly
safe liquid for use in such refrigerators, a liquid that would not be poisonous
and would not explode. Careful research by skilled chemists lead to the
production of a compound of carbon, chlorine, and fluorine that is both
non-poisonous and incombustible, yet which has the right characteristics
for use in an electric refrigerator....again in the search for an ideal liquid
refrigerant for electric refrigerators, Midgley and his assistants were able
in three days of intensive study of the progressive variation of the compounds
of elements arranged in periodic order to settle upon dichloro-difluoromethane,
a non-poisonous, non flammable, easily vaporised liquid.
If Thomas
were alive today what would he say?
The importance of tetraethyl lead for the worlds economy at the time of
its development is greatly underestimated and grossly misrepresented
by some modern writers who, with the benefit of hindsight have castigated
its usefulness. The internal combustion engine became the horse for the
buggy to transport the worlds produce and increase travel to unprecedented
levels, ethyl in no small part contributed to this rise in world economies.
It was the 20-30% power saving that was vital in helping the world
economies to develop and for the Allies to win the Second World War from
1938-1945.
If iodine had been the preferred option for antiknocking then we would
have witnessed major deaths as a result of atmospheric iodine poisoning, lung
degeneration and water pollution. Iodine is a highly corrosive elemental
gas. As a compound forming a salt its effect on the thyroid and growth rates
may have altered the growth of humans and other animals in aqueous ecosystems
irreversibly.
It was the best available option at the time given the development of
scientific knowledge.
We might say that "ethyl" only became a problem when the world demand
for vehicles increased in the post WW2 period, which was concomitant with
world wide consumer demand for higher standards of living irrespective of
any other consideration, such as quality of life.
If dichloro-difluoromethane had not been introduced at the time the demand
for refrigeration was increasing there would have been many more deaths
due to asphyxiation and explosion from ammonia vapours.
Thomas Midgley's work was a brilliant combination of pure scientific
research and its application to the emerging discipline of chemical
engineering, of which Mendeleev would have been justly proud .
The periodic system also has enabled the chemist to find compounds with
certain definite desirable properties. For instance Thomas Midgley Jnr.,
in his search for an anti-knock compound for gasoline was able to predict
that tetraethyl lead would be the best of all the possible compounds before
it had been tried . All his predictions were based on a study of the periodic
arrangement....The antiknock properties of gasoline have been increased by
the addition of tetraethyl lead. Knocking jars the wall of the automobile
cylinders by the explosion instead of steadily pushing the cylinder back.
Knocking represents the wastage of a large percentage of the energy. The wastage
of energy is not the worst thing connected with knocking; it injures the
car. 
If Thomas
were alive today what would he say? 
The importance of tetraethyl lead for the worlds economy at the time of
its development is greatly underestimated and grossly misrepresented
by some modern writers who, with the benefit of hindsight have castigated
its usefulness. The internal combustion engine became the horse for the
buggy to transport the worlds produce and increase travel to unprecedented
levels, ethyl in no small part contributed to this rise in world economies.