In the early 1800s there arose in England a fashion for inhaling nitrous oxide, or laughing gas, 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, the Askesian Society, was for a time devoted to little else. Theaters put on "laughing gas evenings" where volunteers could refresh themselves with a robust inhalation and then entertain the audience with their comical staggerings.

I mention this to make the point that chemistry, having come so far in the 18th century, rather lost its bearing in the first decades of the 19th, in much the way that geology would in the early years of the 20th. Partly it was to do with the limitations of equipment—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 potash and 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 is perhaps telling that one of the most important observations of the century, Brownian motion, which established the active nature of molecules, was made notby a chemist but by a Scottish botanist, Robert Brown.(What Brown noticed, in 1827, was that tiny grains of pollen suspended in water remained indefinitely in motion no matter how long he gave them to settle.The cause of this perpetual motion—namely the actions of invisible molecules—was long a mystery.)