GrumpyOldMan1066

The firepit would have to be reworked to have a stoked vs. non-stoked condition. Fires will burn to embers and then extinguish unless you push new fuel onto the embers. Make the fire unable to cook if not kept up to temp and burn at the slower rate, then to cook, poke it with a stick/firepoker which is boost both temp and fuel consumption for a short length of time. Once that time is done, the fire returns to the lower rate of consumption and the heat subsides. You could match the higher consumption to the the number of pieces of fuel used now to cook. If a pot cooks using 5 units of fuel, poke it 5 times to burn hot that long. If nothing is cooking, a poke should return/bank the fire to the lower rate.

Aqua Vitae and distilled water were the first two readily available chemical purifiers, IIRC. They and the various acids lead to alchemy and thus to chemistry. Somebody well versed enough in historical chemistry practices could probably suggest plenty of uses for all those processes. I know they used various chemical baths to increase output from gold and silver mining, for example, including mercury. Acids were used to etch and inlay/deposity metal, which might lead to etched and multicolored armor and weapons. These processes go back nearly to pre-history. Even without adding in a potion/alchemy system, real world applications for multiple chemical processes start with distilled water and alcohol.