Buyers who dissolve caustic soda flakes into liquor onsite need a working feel for three numbers: concentration, density and freezing point. Getting them wrong shows up as a frozen tank line in winter, or a kettle charged with half-strength lye.
Density Is Your Fast Concentration Check
At 20°C, NaOH liquor density tracks concentration closely enough to run a plant on a hydrometer alone:
- ~20% NaOH: about 1.22 g/cm³
- ~30% NaOH: about 1.33 g/cm³
- ~40% NaOH: about 1.43 g/cm³
- ~50% NaOH: about 1.53 g/cm³
Rule of thumb: every 10 percentage points of NaOH adds roughly 0.10 g/cm³ of density near commercial strengths. A drifting hydrometer reading usually means dilution water flow changed - or the last flake charge was short.
Freezing Points Decide Your Tank Design
NaOH liquor does not behave like water on the way down:
- 50% liquor begins to crystallize around 12°C - in temperate winters it will salt out in untraced lines and tanks.
- 32% liquor stays liquid to roughly 5°C, but is still risky outdoors without heat tracing.
- ~20% liquor resists freezing below -20°C, the choice for cold-climate outdoor storage where tracing is impractical.
If your plant cannot hold tanks above 15°C, either buy flakes and make down a lower strength, or budget for steam/electric tracing and insulated structures from day one.
Why Buy Flakes Instead of Ready Liquor
- Freight economics: 50% liquor is half water by weight. Shipping flakes moves twice the NaOH per container and avoids hazardous-liquid tank container logistics.
- Shelf stability: properly packed 99% flakes store for months; liquor absorbs CO₂ from air and loses strength whenever a tank breathes.
- Flexibility: one stock of flakes serves several liquor strengths for different departments.
Our Recommendation
For onsite make-down we recommend DSC Trading's Caustic Soda Flakes 99% min (GB/T 209-2018 superior grade, ultra-low Fe₂O₃): 25 kg moisture-proof three-ply bags, 25 MT per 20' FCL, every lot with COA and optional SGS inspection. Send us your target liquor strength and ambient temperature range at site - we will suggest a make-down concentration and confirm CIF/FOB pricing within 12 hours.
Keep a density table and hydrometer at the make-down tank, log every batch, and your liquor strength will never be a surprise.