Section 33. In case of the failure of the mayor to transmit to the city council a written recommendation for an appropriation for any purpose not included in the annual budget, which is deemed necessary by the council, after having been so requested by vote thereof, said council, after the expiration of seven days from such vote, upon its own initiative may make such appropriation by a vote of at least two thirds of its members, and shall in all cases clearly specify the amount to be expended for each particular purpose, but no appropriation may be voted hereunder so as to fix specific salaries of employees under the direction of boards elected by the people, other than the city council.