Short answers, pulled from the story.
Sodium carbonate is the inorganic compound Na2CO3, a white, odorless, water-soluble salt that yields alkaline solutions in water. It is also known as washing soda, soda ash, sal soda, and soda crystals.
Sodium carbonate is used as a cleansing agent in soap powders, to soften hard water, and in the manufacture of glass, soap, paper, and other sodium compounds like borax. It also serves in cooking, photographic film developing, swimming pool pH control, fiber-reactive dyeing, and the tanning of animal hides.
In 1861 the Belgian chemist Ernest Solvay developed a method that reacts sodium chloride, ammonia, water, and carbon dioxide to form sodium bicarbonate, which is then heated to make sodium carbonate. The process recycles its ammonia, consumes only brine and limestone, and leaves calcium chloride as its only waste product. By 1900-90 percent of sodium carbonate was produced this way.
Sodium carbonate occurs naturally in arid regions as evaporite deposits formed when seasonal lakes dry up, and the mineral natron was mined from dry lake bottoms in Egypt since ancient times. Trona deposits supply nearly all US consumption, with large deposits found in 1938 near Green River, Wyoming, and important reserves near Ankara, Turkey. It also erupts from Ol Doinyo Lengai in Tanzania and has been identified as the source of bright spots on Ceres.
Sodium carbonate is a stronger base than baking soda but weaker than lye, and its alkalinity affects gluten production and improves browning by lowering the Maillard reaction temperature. It gives Japanese ramen and Chinese lamian noodles their flavor and texture, shapes Cantonese moon cakes and German pretzels, and powers the fizz of sherbet powder. As a food additive it carries the European number E500.
The Leblanc process was patented by the French chemist Nicolas Leblanc in 1792, producing sodium carbonate from salt, sulfuric acid, limestone, and coal via an intermediate called black ash. It released hydrochloric acid as air pollution and calcium sulfide as waste, and it remained the major production method until the late 1880s, with the last plant closing in the early 1920s.
Washing soda is sodium carbonate decahydrate, Na2CO3·10H2O, the most common hydrate of sodium carbonate containing ten molecules of water of crystallization. It is made by dissolving soda ash in water and crystallizing it, and it cleans through saponification, converting fats and grease into water-soluble soaps.