The sinking fund commission shall cause to be kept a separate account for each issue of term bonds and under at least the following classifications: namely, school bonds, water bonds, and general bonds. It may invest all funds under one account and shall distribute and credit to each account the proper proportion of the annual sinking fund appropriation, and also make among such accounts a proportionate distribution of all accretions and interest earned by the sinking fund investment and a like distribution of losses, which distribution shall be made as of December thirty-first of each year.