Every claim which is chargeable against the fund raised for the support of the free public schools of the State, except such as is otherwise provided for by law, must be signed by at least a majority of the board of trustees of the school district against which the claim is chargeable, and the correctness and legality of the same shall be sworn to and subscribed by the person presenting such claim before it shall be approved by the person or persons authorized by law to give such approval. The oath required by this section may be administered by any person authorized to administer oaths either within or without the State. School trustees and county superintendents of education shall, free of charge, administer oaths to persons presenting claims under this section.