To meet casual deficits or failures in revenue, and for necessary expenditures for public purposes, including the erection of public buildings, and for the payment of all Territorial indebtedness assumed by the State, the State may contract debts, not exceeding in the aggregate at any one time, an amount equal to one and one-half per centum of the value of the taxable property of the State, as shown by the last assessment for State purposes, previous to the incurring of such indebtedness. But the State shall never contract any indebtedness, except as provided in Article XIV, § 2, in excess of such amount, and all monies arising from loans herein authorized, shall be applied solely to the purposes for which they were obtained.