The City Council of said City shall provide in the annual budget, beginning with the annual budget next following the due enactment and publication of an ordinance providing for such retirement benefits, disability benefits, and death benefits, or any one or more of them, for City employees and appointive officers, or for either class, and for necessary boards and officers to administer and control such retirement fund or funds and the terms and conditions under which such employees and officers, or either of said classes, may be retired and receive said benefits, an appropriation to any one or more of said funds as may be necessary to meet the required demands thereunder that are not otherwise provided for, and said City Council shall annually, assess, beginning with the annual property tax assessments next following the first such appropriation made, a special tax on the property grand list to provide the funds required for such appropriation.