The author uses the weight of the soldiers' gear to create a motif that helps illustrate the inner state of the characters: by listing every material thing they carried with its weight, a sense of physical heaviness is created, to then introduce the psychological/spiritual weight of the things they are actually carrying in their minds.
It's A. He explains in the excerpt how he thinks it was an impurity that made the draught work. Now that he doesn't have the original salt anymore, the draught isn't working.
