3. By that law, contracts are divided into those which are formed by the mere consent of the parties, and therefore are called consensual; such as sale, hiring and mandate, and those in which it is necessary that there should be something more than mere consent, such as the loan of money, deposit or pledge, which, from their nature, require the delivery of the thing; whence they are called real. Poth. Obl. p. 1, c. 1, s. 1, art. 2.