Coal gas and pneumatic tube: what they have in common

1. Step 1. Coal gas — is made of — Coal. The gas was made by the dry distillation of coal.
2. Step 2. Coal — is material for — Aspirin. The raw materials of early pharmaceutical synthesis were products of coal tar distillation.
3. Step 3. Aspirin — uses — Tablet (medicine). Produced as tablets.
4. Step 4. Tablet (medicine) — works like — Capsule. Dosage forms.
5. Step 5. Capsule — is part of — Pneumatic tube. A container for letters.

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