You are a modern chemist and metallurgist and unexpectedly get sent back in time to the era of Caesar Octavius Augustus. After spending a couple years learning ancient Latin, what changes or improvements could you offer to Roman society?
You know how to make modern metals but could the Romans know how to find the components to make more modern metal alloys? Would they have the heat sources necessary to smelt ores to make modern alloys? Could you at least encourage them to not put lead in their water pipes to cut down on lead poisoning? Could you improve their iron to make something closer to modern steel to make their armor and weapons better? Could you get them to make crude bronze cannons that could be used in sieges or siege defense?
Could you set up chemical disinfectants to help improve food preparation cleanliness and wound care? You do not have advanced medical knowledge but you know cleanliness and germ control could help a LOT! Could you offer them some basic ideas on fertilizers and pesticides? The assumption is you are an expert and very knowledgable but you have no text books or resources you were able to take with you, all you have is your memory. Would that be enough and what would be the most useful? (My personal choice would be fertilizers and disinfectants.)