Germ theory is great, for sure. For the rest, aim a bit lower to reach things you can figure out how to manufacture in your lifetime: working with steel was jus

Germ theory is great, for sure. For the rest, aim a bit lower to reach things you can figure out how to manufacture in your lifetime: working with steel was just starting to be properly understood in 1850s, and pre-industrial seems to be defined as 1750-1850, so depending on exact timing you could perhaps become the greatest blacksmith in existence, or a rich industrialist/inventor. As a modern person, the simplest lessons you can take back on that topic are probably "add more oxygen to the fire", and that some combinations of metals burn in very specific ways (think fireworks, burning magnesium, etc). https://en.wikipedia.org/wiki/Blast_furnace https://en.wikipedia.org/wiki/Blast_furnace https://en.wikipedia.org/wiki/Bessemer_process https://en.wikipedia.org/wiki/Bessemer_process https://en.wikipedia.org/wiki/Open-hearth_furnace https://en.wikipedia.org/wiki/Open-hearth_furnace