whatever was topical—hypnotism； prison reform； therespiration of insects； the water supply of paris。 it was in such a capacity in 1780 thatlavoisier made some dismissive remarks about a new theory of bustion that had beensubmitted to the academy by a hopeful young scientist。 the theory was indeed wrong； but thescientist never forgave him。 his name was jean…paul marat。 the one thing lavoisier never did was discover an element。 at a time when it seemed as ifalmost anybody with a beaker； a flame； and some interesting powders could discover something new—and when； not incidentally； some two…thirds of the elements were yet to befound—lavoisier failed to uncover a single one。 it certainly wasn’t for want of beakers。 lavoisier had thirteen thousand of them in what was； to an almost preposterous degree； thefinest private laboratory in existence。 instead he took the discoveries of others and made sense of them。 he threw out phlogistonand mephitic airs。 he identified oxygen and hydrogen for what they were and gave them boththeir modern names。 in short； he helped to bring rigor； clarity； and method to chemistry。 and his fancy equipment did in fact e in very handy。 for years； he and madamelavoisier occupied themselves with extremely exacting studies requiring the finestmeasurements。 they determined； for instance； that a rusting object doesn’t lose weight； aseveryone had long assumed； but gains weight—an extraordinary discovery。 somehow as itrusted the object was attracting elemental particles from the air。 it was the first realization thatmatter can be transformed but not eliminated。 if you burned this book now； its matter wouldbe changed to ash and smoke； but the net amount of stuff in the universe would be the same。 this became known as the conservation of mass； and it was a revolutionary concept。 unfortunately； it coincided with another type of revolution—the french one—and for this onelavoisier was entirely on the wrong side。 not only was he a member of the hated ferme générale； but he had enthusiastically builtthe wall that enclosed paris—an edifice so loathed that it was the first thing attacked by therebellious citizens。 capitalizing on this； in 1791 marat； now a leading voice in the nationalassembly； denounced lavoisier and suggested that it was well past time for his hanging。 soon afterward the ferme générale was shut down。 not long after this marat was murderedin his bath by an aggrieved young woman named charlotte corday； but by this time it was toolate for lavoisier。 in 1793； the reign of terror； already intense； ratcheted up to a higher gear。 in octobermarie antoinette was sent to the guillotine。 the following month； as lavoisier and his wifewere making tardy plans to slip away to scotland； lavoisier was arrested。 in may he andthirty…one fellow farmers…general were brought before the revolutionary tribunal （in acourtroom presided over by a bust of marat）。 eight were granted acquittals； but lavoisier andthe others were taken directly to the place de la revolution （now the place de la concorde）；site of the busiest of french guillotines。 lavoisier watched his father…in…law beheaded； thenstepped up and accepted his fate。 less than three months later； on july 27； robespierrehimself was dispatched in the same way and in the same place； and the reign of terrorswiftly ended。 a hundred years after his death； a statue of lavoisier was erected in paris and muchadmired until someone pointed out that it looked nothing like him。 under questioning thesculptor admitted that he had used the head of the mathematician and philosopher the marquisde condorcet—apparently he had a spare—in the hope that no one would notice or； havingnoticed； would care。 in the second regard he was correct。 the statue of lavoisier…cum…condorcet was allowed to remain in place for another half century until the second worldwar when； one morning； it was taken away and melted down for scrap。 in the early 1800s there arose in england a fashion for inhaling nitrous oxide； or laughinggas； after it was discovered that its use “was attended by a highly pleasurable thrilling。” for the next half century it would be the drug of choice for young people。 one learned body； theaskesian society； was for a time devoted to little else。 theaters put on “laughing gasevenings” where volunteers could refresh themselves with a robust inhalation and thenentertain the audience with their ical staggerings。 it wasn’t until 1846 that anyone got around to finding a practical use for nitrous oxide； asan anesthetic。 goodness knows how many tens of thousands of people suffered unnecessaryagonies under the surgeon’s knife because no one thought of the gas’s most obvious practicalapplication。 i mention this to make the point that chemistry； having e so far in the eighteenthcentury； rather lost its bearings in the first decades of the nineteenth； in much the way thatgeology would in the early years of the twentieth。 partly it was to do with the limitations ofequipment—there were； for instance； no centrifuges until the second half of the century；severely restricting many kinds of experiments—and partly it was social。 chemistry was；generally speaking； a science for businesspeople； for those who worked with coal and potashand dyes； and not gentlemen； who tended to be drawn to geology； natural history； and physics。 （this was slightly less true in continental europe than in britain； but only slightly。） it isperhaps telling that one of the most important observations of the century； brownian motion；which established the active nature of molecules； was made not by a chemist but by a scottishbotanist； robert brown。 （what brown noticed； in 1827； was that tiny grains of pollensuspended in water remained indefinitely in motion no matter how long he gave them tosettle。 the cause of this perpetual motion—namely the actions of invisible molecules—waslong a mystery。）things might have been worse had it not been for a splendidly improbable character namedcount von rumford； who； despite the grandeur of his title； began life in woburn；massachusetts； in 1753 as plain benjamin thompson。 thompson was dashing and ambitious；“handsome in feature and figure；?