by Roald Hoffmann and Pierre Laszlo
In search of a chemical conversation we are on a farm in Uniow, a little Ukrainian village in Austro-Hungarian Galicia, just before the onset of World War I. In the farm yard we see a big, steaming lead-lined iron pot. The men have mixed some potash in it (no, not the pure chemical with composition KOH from a chemical supply company, but the real ash from burning good poplar) and quicklime, to a thickness that an egg ÿ plenty of eggs here, judging from the roaming chickens ÿ floats on it.
Elsewhere in the yard, women are straining kitchen grease, suet, pig bones, rancid butter, the poor parts skimmed off the goose fat (the best of which had been set to cool, cracklings and all). This mix doesn’t smell good; they would rather toss the kitchen leavings and bones into the great iron pot, but the fat must be free of meat, bones, and solids for the process to work.
They are making soap. Not that we had to go that far, near where one of us was born, for soap was prepared in this way on farms since medieval times well into this century. Fat was boiled up with lye (what the potash and quicklime made). The reaction was slow ÿ days of heating and stirring until the lye was used up, and a chicken feather would no longer dissolve in the brew. One learned not to get the lye on one's hands. The product of a simple chemical reaction was then left in the sun for a week, stirred until a paste formed. Then it was shaped into blocks and set out on wood to dry.
And inside the steaming pot, deep inside, where the fat and the lye are reacting? There is the conversation we are after, a hellishly animated molecular conversation. The lye that formed was an alkaline mixture of KOH, Ca(OH)2 and NaOH. In the vat one had hydroxide (OH-) ions, and K+ , Ca2+ , Na+ all surrounded in dynamic array and disarray by water molecules. Contaminants aside, the fat molecules are compounds called esters, in which an organic base, glycerol, combines with three long-chain hydrocarbon chains. A typical one is stearate:
If we just call this ion Rÿ, then the formula for a fat is roughly