.......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.
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 .
Main Page Previous page