The merger of two Rhode Island accounting firms makes DiSanto, Priest & Co. one of the largest in the smallest state in the union.DiSanto, Priest & Co. announced the aquisition, effective Jan. 1, with Pirolli, Deller & Conaty. The companies did not disclose financial terms. The company hopes to use the added strength to gain market share on the major firms working in the region, the Providence Journal reported Wednesday.The merger creates an accounting and consulting firm with 33 CPA’s, more than 50 accounting professionals and 77 total staff, according to spokesman John J.