Chapter 4: Saponification
1340 Words
With the soda ash in hand, Li Zhi needed quicklime next. Quicklime was a common building material in the Ming Dynasty, and Tianjin Wei naturally had plenty of shops selling it.
This time, Li Zhi didn’t need a guide. Relying on his host's memories, he headed straight for a street in the eastern part of the garrison city known for bricks and tiles, where he purchased the quicklime. At two wen per jin, he bought one jin for his experiment. The saponification reaction required an alkali and fat, so oil was next.
By the late Ming, soybean oil was widely used and cheap. Li Zhi found the vegetable market near Jingbianfang and located an oil stall. "Zhao San, give me four jin of soybean oil."
The oil seller, Zhao San, scowled when he saw it was Li Zhi. "Your family's buried in debt, about to lose your house, and you can still afford oil? Still cooking fancy meals?" Seeing Zhao San picking a fight for no reason, Li Zhi shot back, "Whether my house gets taken or not is none of your business, Zhao San. Are you not doing business anymore?"
Hearing Li Zhi's sharp retort, Zhao San was taken aback. He looked Li Zhi up and down, surprised. Li Zhi had always been slow, letting himself be bullied without a word, which was why Zhao San dared to taunt him. He never expected Li Zhi to be so sharp-tongued today. Stunned for a moment, Zhao San finally quieted down a bit. Still scowling, he said, "You came empty-handed. What are you going to put the oil in?"
Li Zhi fired back, "Don't you give a gourd with the purchase? Stop playing dumb!" Zhao San couldn't figure out how Li Zhi had changed so much, becoming so clever. Reluctantly, he fished out a gourd from under the stall, filled it with four jin of oil, and handed it over. "Thirty wen per jin."
"Four jin is ninety wen. Will you sell it or not? If you do, I'll come back for more tomorrow," Li Zhi stated.
Hearing this, Zhao San finally grasped that Li Zhi was no longer simple-minded—he had genuinely become shrewd. Caught between wanting the sale and saving face, Zhao San thought for a moment before saying gruffly, "Fine, I'll let you have it at that price." Li Zhi passed over the ninety wen and took the oil gourd.
As he handed the gourd to Li Zhi, Zhao San couldn't help asking, "You'll really come back tomorrow to buy more?"
Li Zhi smiled. "If you make it a little cheaper, I'll come buy every day." Fat was a key raw material and would be consumed in the largest quantities. If he could get the oil cheaper, the cost of making soap would drop significantly. It was worth haggling for.
Hearing Li Zhi's business-savvy words, Zhao San finally shifted into proper merchant mode, dropping the bullying attitude. "If you come again tomorrow, we can discuss the price, no problem."
Li Zhi smiled, tied the gourd to his belt, and left the market.
Carrying the oil gourd and two packages of raw materials, Li Zhi returned to his family compound. As he passed by the family shop, his younger brother Li Xing spotted him. Having guarded the shop all day without a single customer for the pepper, Li Xing saw Li Zhi returning with bundles and couldn't help but storm over. "What did you buy all this stuff for? And you bought oil too? You think we don't owe enough money already?" Li Zhi, in his previous dull state, had been deeply looked down upon by his younger brother.
Having just crossed over a few days ago, Li Zhi was still getting his bearings and hadn't spoken much, so he hadn't changed Li Xing's impression of him. Now, seeing Li Zhi spend money on what seemed like useless things, Li Xing launched into a scolding, showing no respect for his older brother.
After a moment, Li Xing decided his simpleton brother must have been cheated. He demanded loudly, "Who told you to buy all this?"
Li Zhi, happy to have gathered his materials, was greeted with a torrent of abuse the moment he returned. He exhaled in frustration before saying, "Li Xing, hold your tongue. Close up the shop and come see your brother work some magic."
Hearing this mysterious pronouncement, Li Xing was dumbfounded. After a pause, he cursed again. "You must have been cheated into buying all this useless junk! Who taught you any 'magic'? Tell me, and I'll go settle the score with them!"
Hearing this, Li Zhi felt imaginary black lines streak down his forehead. Unbelievable. It seemed in his brother's eyes, he was a brainless fool anyone could cheat. Changing that perception would clearly take some work; a few words wouldn't cut it.
"Can't explain it to you. You just stay here and sell your pepper." Not wanting to waste more breath on Li Xing, Li Zhi walked into the house and headed for the kitchen. Li Xing wanted to chase after him and demand an explanation but was afraid to leave the shop unattended, lest someone steal the pepper. He could only punch the wall in frustration, watching Li Zhi go.
Madame Zheng was busy weaving and didn't notice Li Zhi's return. Li Zhi entered the kitchen and began experimenting with his first batch of soap.
In his past life, he had designed soap for a local factory. That project had given him a complete, start-to-finish understanding of soap production. Making soap in this era was no great challenge for him. Even though it was his first time using primitive methods, he proceeded with familiar ease, finding the process straightforward.
He found a large wooden bucket, filled it with well water, and tossed in eight liang of quicklime. With a sharp hiss, the water began to churn and bubble, turning scalding hot. The quicklime reacted with the water to form calcium hydroxide solution—slaked lime—releasing intense heat that warmed the water in the bucket.
Into this bucket of slaked lime, Li Zhi slowly stirred in one jin of soda ash. The moment the soda ash hit, the water seemed to boil violently, sending up a huge plume of steam that instantly vaporized a third of the water, filling the kitchen with mist.
Li Zhi quickly added more cold water to the bucket to lower the temperature. The water was now a murky, opaque mess. The slaked lime (calcium hydroxide) had reacted with the soda ash (sodium carbonate), producing calcium carbonate and sodium hydroxide. The calcium carbonate settled, clouding the water, and the reaction had released enough heat to boil off much of the water.
Li Zhi let the bucket sit for a while. The calcium carbonate gradually settled to the bottom, leaving a transparent layer of sodium hydroxide solution—lye—floating on top. Using a ladle, he carefully scooped the lye solution into another bucket, then filtered it through coarse cloth to remove any remaining calcium carbonate sediment. He kept half of the resulting lye.
He poured this half of the lye into an iron pot, placed the pot on the stove, and used a firestarter and firewood to heat the lye solution. As it warmed, he began slowly adding the soybean oil, stirring constantly with a stick.
As the oil was added, Li Zhi kept stirring. Under heat, the alkali and fat began the saponification reaction. The oil gradually disappeared, and a layer of thick, viscous liquid formed on the surface of the pot. After heating and stirring for about a quarter of an hour, Li Zhi scooped out some of this liquid with a spoon for inspection. Finding traces of unconverted oil still present, he continued adding the remaining lye solution bit by bit.
He repeated this process—stirring, heating, checking, and adding more lye—until all the fat was fully consumed and the thick mixture no longer contained any traces of oil.
- Writer
