General Chemical Industrial Products

Sampling Bulk Shipments

Soda ash can be hard to sample because it absorbs moisture and carbon dioxide from the air through its shipping container and because vibrations in transit can cause particles in bulk dense ash to segregate by size. Soda ash specifications often allow for moisture absorption, e.g., ASTM D 458-74 and Federal Specification O-S-57 1f.

Details of good sampling depend on the type of shipment (container or bulk), the type of product (light or dense soda ash) and the type of analysis desired. The latter involves chemical and physical analyses and whether the quality to be determined is "as shipped," "as received," or "as used."

Although bulk soda ash shipments are normally in transit a relatively short time, some absorption of moisture and carbon dioxide by surfaces exposed to the atmosphere is likely. In sampling a hopper car for chemical analysis, brush the surface layer aside to a depth of about 4 in. and take product from the exposed area. Samples from various parts of the car can be taken and composited.

For physical tests, such as sieve analysis, sample at a depth of at least 12 in. The best sampling points are near the discharge points of hopper cars and bulk pneumatic transports. Conveying systems, especially pneumatic conveyors, tend to break down particle size and so can cause the absorption of moisture andcarbon dioxide to increase.

A representative sample usually involves collecting about 1 cu. ft. in total per carload. Never fill the sampling cup or other container more than levelfull so larger grains do not roll off. The composite sample should be reduced in volume by "quartering" to a suitable size for analysis.

Sampling Containers

Sample packaged soda ash by taking samples near the center of the package. This can be done by removing the top 6 to 8 in. from the package and sampling from the center of the remaining portion. Such a sample is generally representative except when storage was lengthy or involved damp conditions.

Packaged soda ash stored for an extended time can be sampled only after emptying the package and mixing the contents thoroughly. The sample taken is likely to represent only the package sampled and not the entire stock of packages, because those in the outer layer of a storage pile most likely absorbs more moisture and carbon dioxide than those deeper in the stock.

To estimate how much moisture and carbon dioxide absorption has occurred, compare the weight of the full container to the original gross weight. Absorption increases weight and reduces the percent of sodium carbonate present, although the total alkali content remains the same. Some of the sodium carbonate may be converted to sodium bicarbonate due to absorption, but this is not important in most cases.

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