Tallow and fuel cell: what they have in common

1. Step 1. Tallow — is used in — Oil lamp. The fuel was animal fat, later oil.
2. Step 2. Oil lamp — evolved into — Incandescent light bulb. The electric lamp replaced oil and gas lamps.
3. Step 3. Incandescent light bulb — is part of — Torch (flashlight). A bulb (today an LED).
4. Step 4. Torch (flashlight) — has part — Dry cell. Batteries.
5. Step 5. Dry cell — uses — Electrochemical reaction. A chemical source of current.
6. Step 6. Electrochemical reaction — is used in — Fuel cell. The reaction runs electrochemically, without combustion.

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