Which blending method involves mixing by tumbling in a closed container?

The blending method that involves mixing by tumbling in a closed container is tumbling. This technique is often used in the pharmaceutical industry to achieve a uniform distribution of ingredients in a powder form. The tumbling action ensures that the powders are mixed thoroughly without introducing moisture or air into the blend, which is crucial for maintaining the integrity of the components being blended.

This method is particularly effective for large quantities of powders, as it can accommodate various particle sizes and shapes, ultimately leading to a consistent mixture. The closed container also helps prevent contamination from the surrounding environment, ensuring the quality of the pharmaceutical product.

In contrast, the other methods mentioned—spatulation, trituration, and granulation—utilize different principles for blending. Spatulation involves manual mixing on an ointment slab, trituration typically refers to grinding powders to achieve finer particle size, and granulation combines particles to form granules, which is a different process used primarily to improve the flow and compaction of powders. Therefore, tumbling is the most appropriate choice for this specific blending method.