Busy as he was in spreading his religious tenets, in fraternizing with congenial scientific friends, his thoughts would involuntarily turn back to England: Here, though I am as happy as this country can make me ... I do not feel as I did in England. By May, 1796, he had finished his discourses, although he proposed concluding with one emphatically Unitarian in character. This was expected by his audience, which had been quietly prepared for it and received it with open minds and much approval. On his return to Northumberland he promptly resumed his work on the "Church History," but was much disturbed because of the failure of his correspondents in writing him regularly, so he became particularly active in addressing them. But better still he punctuated his composition of sermons, the gradual unfolding of his Church History, and religious and literary studies in general, with experimental diversions, beginning with the publication (1796) of an octavo brochure of 39 pages from the press of Dobson in Philadelphia, in which he addressed himself more especially to Berthollet, de la Place, Monge, Morveau, Fourcroy and others on "Considerations on the Doctrine of Phlogiston and the Decomposition of Water." It is the old story in a newer dress. Its purpose was to bring home to Americans afresh his particular ideas. The reviewer of the _Medical Repository_ staff was evidently impressed by it, for he said: It must give pleasure to every philosophical mind to find the United States becoming the theatre of such interesting discussion, and then adds that the evidence which was weighty enough to turn such men as Black and others from the phlogiston idea to that of Lavoisier-- has never yet appeared to Dr. Priestley considerable enough to influence his judgment, or gain his assent. Priestley, as frequently observed, entertained grave doubts in regard to the constitution of metals. He thought they were "compounded" of a certain earth, or calx, and phlogiston. Further he believed that when the phlogiston flew away, "the splendour, malleability, and ductility" of the metal disappeared with it, leaving behind a calx. Again, he contended that when metals dissolved in acids the liberated "inflammable air" (hydrogen) did not come from the 'decompounded water' but from the phlogiston emitted by the metal.