Density Column

Layer six immiscible liquids in a tall glass to build a visible density gradient, then float objects at their natural level

Difficulty: Easy | Time: 10–15 minutes | Visual Impact: Very High

Historical Context

Density — mass per unit volume — is one of the most fundamental physical properties of matter. Archimedes famously described buoyancy in the 3rd century BCE: an object immersed in fluid experiences an upward force equal to the weight of fluid it displaces. If the object is denser than the fluid, it sinks; less dense, it floats.

Sailors and winemakers in the ancient world used floating instruments (hydrometers) to measure fluid density long before the physics was formally understood. The density column makes this invisible property immediately visible by revealing that ordinary household liquids exist at a wide range of densities — some nearly twice as dense as water — and that they separate cleanly because they do not dissolve in each other.

Materials

  • Honey — 50 mL
  • Corn syrup (light or dark) — 50 mL
  • Dish soap — 50 mL
  • Water (with food coloring) — 50 mL
  • Vegetable oil — 50 mL
  • Rubbing alcohol (70% isopropanol, tinted with food coloring if desired) — 50 mL
  • Tall glass, graduated cylinder, or clear vase — at least 400 mL capacity
  • Pouring spoon or pipette
  • Small objects to float: grape, cherry tomato, small plastic bead, cork, raisin, rubber eraser piece

Procedure

  1. Pour honey into the bottom of the tall container — move slowly to avoid splashing
  2. Tilt the container slightly and pour corn syrup slowly down the inside wall
  3. Add dish soap the same way
  4. Gently spoon colored water onto the surface so it doesn’t disturb the soap layer
  5. Slowly pour vegetable oil down the side — wait 30 seconds between each layer
  6. Finally, pour the tinted rubbing alcohol very slowly over the back of a spoon held just above the surface
  7. Wait 2–3 minutes for layers to settle and sharpen
  8. Gently drop in the small objects one at a time; observe where each comes to rest

The Science

Density (ρ = m/V, in g/mL or kg/m³) determines how liquids stack. These liquids are immiscible — they do not dissolve in each other — so instead of mixing they form distinct horizontal layers, with the densest at the bottom.

Approximate densities:

Liquid Density (g/mL)
Honey 1.36–1.45
Corn syrup 1.33–1.38
Dish soap 1.03–1.06
Water 1.00
Vegetable oil 0.91–0.93
Rubbing alcohol (70%) 0.87–0.89

Objects settle at the interface whose density matches their own. A grape (~1.10 g/mL) sinks below water but floats on dish soap. A cork (~0.12 g/mL) sits on top of the alcohol.

Immiscibility arises from polarity: water and alcohols are polar; oils are nonpolar. The saying “like dissolves like” applies to miscibility as well — polar liquids mix with each other, and so do nonpolar ones, but the two groups resist mixing. Honey and corn syrup are aqueous (water-based) and polar, so in theory they could mix with water given enough time and agitation — the column is a kinetic stability, not an absolute thermodynamic one.

Tips

  • Pour slowly — turbulence mixes the layers
  • Using a pipette or squeeze bottle for the lighter layers gives better control
  • If layers mix, wait — they will sometimes re-separate over 10–20 minutes
  • The column can be capped and kept for days as a display

Resources