Paper feed rollers and syringe: what they have in common

1. Step 1. Paper feed rollers — is part of — Fax. Rollers feed the sheet.
2. Step 2. Fax — uses — Electrochemical reaction. The paper darkened under current.
3. Step 3. Electrochemical reaction — is used in — pH meter. A glass electrode.
4. Step 4. pH meter — is made of — Silver. The internal electrode is silver chloride.
5. Step 5. Silver — is material for — Syringe. Early needles were silver.

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