Section 18. Whenever in the opinion of the commissioner an excessive loan has been made, or is about to be made, upon real estate, by a bank, said commissioner may cause an appraisal of such real estate to be made at the expense of the bank making the loan. One appraiser shall be named by the commissioner, one by the bank, and a third by the two thus named. The appraisers shall determine the value of the real estate and certify the same, in writing, to the commissioner and to the bank. If it appears from the appraisal that the loan is excessive, the commissioner may make such order in relation thereto as he deems advisable.