Salt Brine Batch Salinity, Salometer, and Freeze Point

THE TARGET IS 23.3 PERCENT SODIUM CHLORIDE BY WEIGHT AND IT IS NOT A PREFERENCE -- it is the eutectic, the concentration at which the mixture freezes at its lowest possible temperature, about -6 degF. Moving away from it in EITHER direction raises the freezing point, which is why every brine operation in the country mixes to the same number. THE TWO FAILURE DIRECTIONS LOOK NOTHING ALIKE. Over-concentrated brine carries salt it cannot hold, which crystallises in tanks, lines, screens and nozzles and produces an intermittent spray pattern and a maintenance backlog -- annoying, and it takes the truck out of service in the middle of an event. Under-concentrated brine sprays perfectly and freezes on the road, which is WORSE, because it looks like a successful application right up until the pavement ices. A batch mixed to 20 percent instead of 23.3 saves a few hundred pounds of salt and gives away roughly eight degrees of freezing point, landing near +2 degF -- a temperature the road will reach on any clear night. VERIFY EVERY BATCH, AND VERIFY IT WITH AN INSTRUMENT. A salometer is a hydrometer scaled in percent of saturation, and 23.3 percent by weight is about 88 salometer; the scale is referenced to a stated temperature, commonly 60 degF, and a hydrometer dropped into cold brine READS HIGH -- which is exactly when a crew is most likely to check it. Counting bags is not verification. AND BRINE IS ANTI-ICING, NOT DEICING, which decides when it is useful at all. Applied to dry pavement before a storm it prevents snow from bonding, which is what lets the plow scrape to bare pavement afterwards with far less salt. Applied to snow that has already fallen it is adding water to the problem. The whole economic case for brine is the material it saves later, and that case is only available to an operation that can apply it in advance. This is a batch calculation on entered figures. Brine density varies with concentration and temperature and the figure entered here is nominal; a measured density or salometer reading on the actual batch is what verifies a mix. Freezing points quoted for chloride solutions are for the pure system, and a working brine picks up dissolved and suspended material from the salt, the water and the tank that shifts its behaviour. It does not address brine from other chlorides or blended with organic additives, corrosion inhibitors or agricultural by-products, all of which change the concentration target, the freezing point and the handling entirely -- a blend is formulated by its supplier, not by this arithmetic. It does not address making equipment, salt quality and insolubles, storage and settling, agitation, or the application rate and timing that decide whether an anti-icing programme works. The material supplier's data, a salometer or density verification of each batch, and the applicable agency policy govern.

batch weight = gallons x brine density; salt = batch weight x concentration; water is the balance by weight, converted at 8.345 lb per gallon; salometer = concentration / saturation concentration x 100; the freezing point is read off the published NaCl curve.

The sodium chloride eutectic at 23.3% by weight and about -6 degF, and the NaCl freezing-point curve linearly interpolated between 0, 5, 10, 15, 20 and 23.3%. Brine density is ENTERED and nominal.

A weight balance and a published phase-diagram interpolation.

Estimate. AHJ and licensed professional govern.

Field names used by the API: batch_gal, target_pct, brine_density_lb_gal, saturation_pct, alt_pct, batch_weight_lb, salt_lb, salt_tons, water_lb, water_gal, salt_per_1000gal_lb, salometer, freeze_point_f, alt_salt_lb, alt_freeze_point_f, salt_difference_lb

• Eutectic concentration 23.3% NaCl by weight, freezing about -6 degFthe sodium chloride phase diagram
• Freezing points are for the pure system a working brine picks up dissolved and suspended materialthe published NaCl curve
• Density is nominal and entered about 9.8 lb per gal at 23.3%; verify the batchthe material supplier's data