Brief description

A hydrometer is an instrument used to measure the density (specific gravity) of a liquid. It is a fundamental tool for monitoring chemical processes and ensuring the quality of fermented products.

Use / Function

• Fermentation Control: Monitoring the conversion of sugar to alcohol in Fermentation.
• Purity Testing: Checking the concentration of solutions like brine or acids.
• Quality Control: Verifying the density of milk or other liquid resources.
• Scale: Small-scale (domestic) to industrial use.

Operating principle

The hydrometer operates based on Archimedes’ principle: a solid body floats in a liquid at a depth proportional to the weight of the liquid it displaces.

• In a dense liquid (high sugar/salt), the hydrometer floats higher.
• In a light liquid (high alcohol), the hydrometer sinks deeper.

How to create it

Minimum functional version

1. Tube: A thin, hollow Glass tube (or a sealed reed).
2. Weighting: Place a small amount of Lead shot or dry sand at the bottom of the tube so it floats upright.
3. Sealing: Seal the top with Beeswax or Glue to prevent water from entering.
4. Calibration:
   • Place it in pure Water and mark the level on a Paper scale inside the tube as “1.000”.
   • Place it in a known concentration (e.g., 10% salt water) to mark a second point and create a linear scale.

Materials needed

• Essential materials:
  • Glass or transparent plastic tube.
  • Lead, small stones, or dry sand (for ballast).
  • Paper (for the scale).
  • Beeswax or resin (for sealing).
• Tools:
  • Kiln or heat source to shape glass.
  • Ruler for marking the scale.

Variants and improvements

• Alcoholometer: Specifically calibrated to measure alcohol concentration in Alcohol.
• Saccharometer: Calibrated to measure sugar content in syrups.
• Thermometer integration: Advanced versions include a thermometer to correct for temperature-induced density changes.

Limits and risks

• Fragility: Usually made of glass and easily broken.
• Temperature sensitivity: Liquids change density with temperature; measurements must be corrected if the liquid is not at the calibration temperature.
• Surface Tension: Bubbles clinging to the tube can cause inaccurate (high) readings.