In the event that any general tax or special assessment levied by any special charter city which collects its own taxes, or any installment of any such assessment, shall remain unpaid for two years or more after any delinquency in payment thereof, then such city may, at any regular sale for taxes thereafter, purchase any such real estate for the full amount of the general taxes, with interest, penalties and costs of advertising, for which the same shall be offered and for such further amount, if any as such city may elect, not to exceed the amount of the special assessments or installments thereof, with interest and penalties, for which the same may be offered. Payment to the extent of the amount of such general taxes, with interest, penalties, and costs of advertising, shall be made, without any necessity or prerequisite of appropriation therefor, by charging the respective funds to which such general taxes, interest, penalties, and costs shall be payable, in the amounts so payable, and, to the extent of any further amount, shall be made from the improvement fund of said city, which funds it is hereby authorized to expend for the purposes stated.