Whenever there is in the treasury to the credit of the Unclaimed Property Fund the sum of twenty thousand dollars ($20,000) or more, the Director of Finance shall invest all but ten thousand dollars ($10,000) in the bonds specified in this article. No investment shall be made which will reduce the uninvested portion of the fund below the amount of ten thousand dollars ($10,000), and whenever a demand presented against the fund will reduce the amount of cash therein below ten thousand dollars ($10,000), the director shall sell such bonds belonging to the fund as he deems proper, so as to restore the cash retention of ten thousand dollars ($10,000).