The amount of seven hundred dollars ($700) of the fund shall constitute a revolving fund and may be drawn upon the warrant of the president and secretary of the board without being audited in the usual manner, in cases of emergency or where cash advances are necessary. However, after the sum of seven hundred dollars ($700) has been so expended, no further warrant shall be drawn on the revolving fund until expenditures previously made from it shall be substantiated by vouchers and itemized statements and audited. All expenditures from the revolving fund shall, at the end of each fiscal year, or at any other time when demand therefor is made by the Director of Finance or by the State Controller, be so substantiated and audited unless previously done.