In the study of hydrates, n-butane is an interesting anomaly (Ng and Robinson, 1976). By itself, n-butane does not form a hydrate; however, its size is such that it can fit into the large cages of the Type II hydrate lattice. Thus, in the presence of another hydrate former, n-butane can enter the cages.

Based on the observed behavior of n-butane, the location of the last shaded section is established; n-butane is a transition component. Molecules smaller than n-butane are hydrate formers, whereas molecules larger than n-butane do not form Type I or Type II hydrates.