Cotton gin and refrigerator: what they have in common

1. Step 1. Cotton gin — has part — Crank. The drum was turned by a handle.
2. Step 2. Crank — is part of — Ice cream maker. A handle.
3. Step 3. Ice cream maker — uses — Latent heat. Ice with salt draws away heat.
4. Step 4. Latent heat — is used in — Ice house. Melting ice absorbs heat.
5. Step 5. Ice house — evolved into — Refrigerator. The refrigerator replaced natural ice.

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