ymptoms associated with overexposure areblindness； insomnia； kidney failure； hearing loss； cancer； palsies； and convulsions。 in its mostacute form it produces abrupt and terrifying hallucinations； disturbing to victims andonlookers alike； which generally then give way to a and death。 you really don’t want toget too much lead into your system。 on the other hand； lead was easy to extract and work； and almost embarrassingly profitableto produce industrially—and tetraethyl lead did indubitably stop engines from knocking。 so in1923 three of america’s largest corporations； general motors； du pont； and standard oil ofnew jersey； formed a joint enterprise called the ethyl gasoline corporation （later shortenedto simply ethyl corporation） with a view to making as much tetraethyl lead as the world waswilling to buy； and that proved to be a very great deal。 they called their additive “ethyl” because it sounded friendlier and less toxic than “lead” and introduced it for publicconsumption （in more ways than most people realized） on february 1； 1923。 almost at once production workers began to exhibit the staggered gait and confusedfaculties that mark the recently poisoned。 also almost at once； the ethyl corporationembarked on a policy of calm but unyielding denial that would serve it well for decades。 assharon bertsch mcgrayne notes in her absorbing history of industrial chemistry；prometheans in the lab； when employees at one plant developed irreversible delusions； a spokesman blandly informed reporters： “these men probably went insane because theyworked too hard。” altogether at least fifteen workers died in the early days of production ofleaded gasoline； and untold numbers of others became ill； often violently so； the exactnumbers are unknown because the pany nearly always managed to hush up news ofembarrassing leakages； spills； and poisonings。 at times； however； suppressing the newsbecame impossible； most notably in 1924 when in a matter of days five production workersdied and thirty…five more were turned into permanent staggering wrecks at a single ill…ventilated facility。 as rumors circulated about the dangers of the new product； ethyl’s ebullient inventor；thomas midgley； decided to hold a demonstration for reporters to allay their concerns。 as hechatted away about the pany’s mitment to safety； he poured tetraethyl lead over hishands； then held a beaker of it to his nose for sixty seconds； claiming all the while that hecould repeat the procedure daily without harm。 in fact； midgley knew only too well the perilsof lead poisoning： he had himself been made seriously ill from overexposure a few monthsearlier and now； except when reassuring journalists； never went near the stuff if he could helpit。 buoyed by the success of leaded gasoline； midgley now turned to another technologicalproblem of the age。 refrigerators in the 1920s were often appallingly risky because they useddangerous gases that sometimes leaked。 one leak from a refrigerator at a hospital incleveland； ohio； in 1929 killed more than a hundred people。 midgley set out to create a gasthat was stable； nonflammable； noncorrosive； and safe to breathe。 with an instinct for theregrettable that was almost uncanny； he invented chlorofluorocarbons； or cfcs。 seldom has an industrial product been more swiftly or unfortunately embraced。 cfcs wentinto production in the early 1930s and found a thousand applications in everything from carair conditioners to deodorant sprays before it was noticed； half a century later； that they weredevouring the ozone in the stratosphere。 as you will be aware； this was not a good thing。 ozone is a form of oxygen in which each molecule bears three atoms of oxygen instead oftwo。 it is a bit of a chemical oddity in that at ground level it is a pollutant； while way up in thestratosphere it is beneficial； since it soaks up dangerous ultraviolet radiation。 beneficial ozoneis not terribly abundant； however。 if it were distributed evenly throughout the stratosphere； itwould form a layer just one eighth of an inch or so thick。 that is why it is so easily disturbed；and why such disturbances don’t take long to bee critical。 chlorofluorocarbons are also not very abundant—they constitute only about one part perbillion of the atmosphere as a whole—but they are extravagantly destructive。 one pound ofcfcs can capture and annihilate seventy thousand pounds of atmospheric ozone。 cfcs alsohang around for a long time—about a century on average—wreaking havoc all the while。 they are also great heat sponges。 a single cfc molecule is about ten thousand times moreefficient at exacerbating greenhouse effects than a molecule of carbon dioxide—and carbondioxide is of course no slouch itself as a greenhouse gas。 in short； chlorofluorocarbons mayultimately prove to be just about the worst invention of the twentieth century。 midgley never knew this because he died long before anyone realized how destructivecfcs were。 his death was itself memorably unusual。 after being crippled with polio；midgley invented a contraption involving a series of motorized pulleys that automatically raised or turned him in bed。 in 1944； he became entangled in the cords as the machine wentinto action and was strangled。 if you were interested in finding out the ages of things； the university of chicago in the1940s was the place to be。 willard libby was in the process of inventing radiocarbon dating；allowing scientists to get an accurate reading of the age of bones and other organic remains；something they had never been able to do before。 up to this time； the oldest reliable dateswent back no further than the first dynasty in egypt from about 3000b。c。 no one couldconfidently say； for instance； when the last ice sheets had retreated or at what time in the pastthe cro…magnon people had decorated the caves of lascaux in france。 libby’s idea was so useful that he would be awarded a nobel prize for it in 1960。 it wasbased on the realization that all living things have within them an isotope of carbon calledcarbon…14； which begins to decay at a measurable rate the instant they die。 carbon…14 has ahalf…life—that is； the time it takes for half of any sample to disappear1?