Ezra Pound uses the classic technique of the evocative power of sounds in his scheme (a kind of figure of speech) for evoking emotion in "Taking Leave of a Friend." The image of "Blue mountain" and "White river" evoke a slow contemplative feeling that is turned suddenly into a sad emotion when the next line requires making "separation." The vowels of the first two lines enhance the imagery evoked by the words describing nature because they are all round vowels of prolonged duration.
These come into conflict with the sorrow evoking third line with its more closed vowels and harsh sounding /t k h s p/ consonants. The fourth line of the first quatrain (four lines) evokes a sense of desolation by the inclusion of the word "dead." Change any of these elements, and a different emotion altogether may be evoked. The second quatrain evokes a feeling of anxiety partly because the vowels scattered between harsh consonants give an unsettled feeling to the nature imagery of a "wide cloud" and the parting of the sun at sunset.