The county of Mobile, through its constituted governing authorities, may levy and collect for public school purposes, a rate of taxation, on the property situated therein, not exceeding in the total of any one year, one-fifth ( 1/5) of one (1) per centum of the value of such property as assessed as provided by the Constitution of Alabama and the statutes now or hereafter enacted pursuant to the said Constitution of Alabama, which said one-fifth ( 1/5) of one (1) per centum shall be in addition to taxes levied and collected under and pursuant to the authority of section 215 of the Constitution of Alabama of 1901, and taxes levied and collected under and pursuant to article XIX of the Constitution of Alabama of 1901, which article XIX was added to said Constitution by amendment; and existing laws attempting or purporting to authorize, empower and direct the said constituted authorities of the county of Mobile to levy and assess such a special tax in addition to the taxes levied and collected under and pursuant to section 215 of the Constitution as aforesaid and taxes levied and collected under and pursuant to article XIX of the Constitution as aforesaid are hereby validated and confirmed.