The assessors, however elected, shall constitute a board of assessors for the city, who shall perform all the duties relative to taking the inventory and the appraisal of property for taxation, and in regard to the assessment and abatement of taxes and issuing warrants for the collection of the same, as are now or may hereafter be required by law of selectmen and assessors of towns; and shall have all the powers and be subject to the same liabilities, in regard to those duties, which selectmen and assessors in towns now or hereafter may have, or be subject to, in regard to the same.