copperas

A student adds copperas to a beaker of clear liquid in the chemistry lab.

Definition

1. Noun (Chemistry):
   • Iron(II) sulfate heptahydrate: "copperas" refers to a green, crystalline compound (FeSO₄·7H₂O), historically known as green vitriol, used in dyeing, ink-making, and as a mordant.
   • General term for metallic sulfates: In older usage, "copperas" could denote various crystalline sulfates, especially those of iron, copper, or zinc, but it most commonly specifies the iron salt.

Usage Examples

• (Iron(II) sulfate used as a mordant in dyeing.)
• (The green crystalline compound used to produce ink.)
• (Iron(II) sulfate applied to crops.)

Advanced Usage

• "Green copperas": a historical synonym for iron(II) sulfate heptahydrate, distinguishing it from other colored vitriols (e.g., blue copperas for copper sulfate).

  • The apothecary stocked green copperas for medicinal preparations. (The green crystalline form of iron sulfate.)

• "Copperas stone": a mineral form of iron(II) sulfate, often found in weathered pyritic rocks.

  • Miners occasionally collected copperas stone from abandoned tunnels. (The naturally occurring crystalline sulfate.)

Variants and Related Words

• Copperas (n) is a direct borrowing from Old French , ultimately from Latin ("rose of copper"), though the compound itself contains no copper.
• Vitriol (n): a broader term for crystalline sulfates, including copperas (green vitriol), blue vitriol (copper sulfate), and white vitriol (zinc sulfate).
  • Green vitriol is another name for copperas. (Iron(II) sulfate heptahydrate.)

Synonyms

• Green vitriol: a historical synonym emphasizing the green color and vitreous crystal form.
• Iron(II) sulfate: the modern chemical name for the compound.
• Ferrous sulfate: an alternative chemical designation (FeSO₄·7H₂O).

Related Idioms

• (No idiomatic expressions directly use "copperas," as it is a technical term largely confined to chemistry and historical contexts.)