"Another example will help clarify this one. The gun maker builds a two-way gun but does not seal either end. If the tube is of the same dimension from one end to the other, the projectiles ejected from both ends could be the same size, but if he made one end larger than the other the projectiles ejected from one end would be smaller than those ejected from the other end. For this reason we say that carbon, sodium-chloride, or potassium-bromide would give equal projections from each end, for they are mated pairs, whereas sodium or potassium alone would give as unequal results as unequally mated pairs, and sodium-bromide, or potassium-iodide would give as unequal results in such an experiment as their cube crystals are distorted, and for the same reason." [Atomic Suicide, page 293]
See Also
iodide
potassium
potassium-bromide
potassium-chloride
sodium iodide