Excess funds investments shall not be made in any stock or obligation unless:
(a) The stock or obligation qualifies as a sound investment.
(b) In case of a purchase, the price paid for the security is not in excess of the current market value at the date of purchase.
(c) In case of a loan, the amount loaned does not exceed eighty-five per cent of the market value, at the date of the loan, of the collateral taken as security.