As the favorite student of Zingarelli, Mercadante turned his compositional interests from instrumental music to the genre of opera. His debut of "Elisa e Claudio" was reminiscent of Rossini's style (1820). This opera brought him international fame. After spending time in Spain and Portugal, away from Naples, and, while serving at Novara Cathedral between 1826 and 1830 as a master of the chapel, he completely rethought his operatic manner of composition. Mercadante's "Il giuramento" premiered in 1837 and continued the musical expressions he had been incubating for the previous ten years. This opera clearly marked a transition in opera and reforms for which Mercadante is noted. The purpose within the texture of the music demonstrably accentuated a new seriousness and dramatic tension. By the decade of the 1840s Mercadante had become the leading figure in Italian opera and had also acceded to the position of the director of the Naples Conservatory. By this time, however, he had also re-fermented an interest in instrumental music, sacred church music and teaching. One reason that he may have turned from opera composition was an envy of the success of Verdi's scores, which comparably, despite Mercadante's influence upon Verdi, were much more innovative and contemporary. He composed approximately sixty operas and characteristically varied the structure of the scores and the accompaniments and removed orchestral touches which had been used simply for effect. Mercadante reformed the complex vocal lines toward a less difficult format and scored the music so that the drama of the libretto could unfold more clearly. ~ Keith Johnson, Rovi