Sampling of Bulk Shipments

It is always advisable to positively identify the caustic soda solution before it is unloaded. If a retainer sample is taken, it must be representative of the entire shipment. Since impurities (especially sodium carbonate) tend to concentrate at the top or bottom of the container, dipping caustic soda solution from the surface will not provide a representative sample. To be representative, the sample must include material from all levels of the tank car or tank truck.

As caustic soda solution freezes, the caustic soda concentration changes in both the solid and liquid phases. This is also true of the impurities present. Consequently, a shipment of partially frozen caustic should be thoroughly thawed before a sample is taken. The freezing and thawing of a caustic soda solution has no effect on the quality of the product. However, it is typical for the caustic soda solution to become cloudy due to precipitated salt.

Commercial samplers are available from chemical equipment supply houses. However, a representative sample can be obtained by rapidly lowering a weighted, small-necked bottle to the bottom of the shipping container and then retrieving it. Caustic soda solution will bubble into the bottle as it is raised, giving a vertical cross-section sample of the container’s entire contents.

The caustic soda solution enters the sampler continuously from the various depths through which it passes. In order to obtain a sample representative of the shipment, the sampler must be kept in motion. The sampling device should then be thoroughly rinsed with water to remove all caustic after each use. Some means should be provided for collecting and safely disposing of all rinse water.


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