Planetary gear and petri dish: what they have in common

1. Step 1. Planetary gear — is part of — Watt steam engine. Watt’s “sun and planet” gear got around the patent on the crank.
2. Step 2. Watt steam engine — uses — Coal. Steam engines were fired with coal.
3. Step 3. Coal — is material for — Synthetic dye. Aniline from coal tar.
4. Step 4. Synthetic dye — evolved into — Sulfonamides. Prontosil was a red dye.
5. Step 5. Sulfonamides — works like — Antibiotic. The first mass-market antibacterial drugs were synthetic sulfonamides; penicillin was discovered earlier (1928) but went into production later.
6. Step 6. Antibiotic — uses — Petri dish. Fleming noticed mould in a Petri dish.

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