https://en.wikipedia.org/wiki/Kaliapparat

The first step, as people have elaborated below, is combust the compound and measure the weights of various oxides, which (after the atomic masses of the relevant elements were settled around the 1820s) lets you work out the empirical formula of an unknown molecule. For benzene, this would tell you that there is 1 C : 1 H, but this doesn't tell you if it's C₄H₄ or C₆H₆ or C₁₁₁H₁₁₁.

The second step is to determine the molar mass of your compound, which requires finding something that depends on the amount of substance but not the mass directly. (In modern times, this is primarily mass spec). Back in the 19th century, this is probably abusing the ideal gas law, which lets you compute the number of moles in a gas given the pressure, temperature, and volume of a vessel. Combine this with the mass of that container, and you know how much a mole weighs. If you get out, say, 77g/mol, and you know that the ratio is 1 C : 1 H, well, the only formula that makes sense is C₆H₆ (which should ideally have 78g/mol, but you might not get the right answer for various experimental reasons).

Funny enough benzene used to be used (a hundred years ago) for aftershave and even for douches. I don't even want to think about what that did to those people's bodies.

When an alarming number of friends (all under 40 years old) from the same small neighborhood in my hometown were diagnosed with leukemia I started to look into the superfund site nearby. The pond that is connected to the stream that supplies the municipal wells in the area was still disgusting (with visible oily residue on the surface) nearly 15 years after the company, Congoleum, stopped operations and the plant was demolished. Soil testing some years earlier revealed benzene, which has been linked to AML.

(I had the impression from somewhere else that his "reverie or day-dream" might have instead been a pipe dream — as in the literal pipe dream (opium?). But I can now find nothing to substantiate this at all so, maybe just ignore.)

EDIT: perhaps I was reading too much into this page from the Golden Book of Chemistry: https://www.slideshare.net/slideshow/the-golden-book-of-chem...

For me, no other story from Chemistry is as fascinating as Kekule dreaming up Benzene’s molecular structure. An important reminder to me about the power of narrative and storytelling.

The answer is probably because the author hasn't taken organic chem and so never heard the story.

When I read a "History of Organic Chemistry" textbook, Kekule and Benzene were essentially the springboard.

https://i.imgur.com/EGyYmkX.jpg

https://www.nytimes.com/1988/08/16/science/the-benzene-ring-...

Wow, what are the chances he discovers something with a name like that?

A beacon of hope for those of us without doctorates in physics out here...

Benzene is used mainly as an intermediate to make other chemicals, above all ethylbenzene (and other alkylbenzenes), cumene, cyclohexane, and nitrobenzene. More than half of the entire benzene production is processed into ethylbenzene, a precursor to styrene, which is used to make polymers and plastics like polystyrene. Some 20% of the benzene production is used to manufacture cumene, which is needed to produce phenol and acetone for resins and adhesives. Cyclohexane consumes around 10% of the world's benzene production; it is primarily used in the manufacture of nylon fibers, which are processed into textiles and engineering plastics. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides.

It's an important feedstock in the chemical industry but it is no longer used directly in household products. It used to be common in solvent/glue/grease remover formulations before the health hazard was widely appreciated.

It's a little like asking "what are the uses of water in chemistry", where you're tempted to answer, "um, everything?" Not quite, but not that far off either. (And with more cancer of course.)

Edit: disclaimer, I'm not a chemist, just an interested layman.

The beans were soaked in warm water then rinsed (several times?) with benzene, which was able to extract the majority of caffeine, and presumably not much else affecting the flavour.

It would have the benefit of evaporating with no residue given enough time, but due to the possibility of residue and the difficulty of working with it safely, decaffeination processes have since moved on.

Quip: Every chemical researcher's #1 need is for research funding, no?