A contract by which one of the contracting parties, called the "seller," enters into an obligation to the other to cause him to have freely, by a title of proprietor, a thing, for the price of a certain sum of money, which the other contracting party, called the "buyer," on his part obliges himself to pay. Poth. Cont.; Civ. Code La. 1000, art. 21.10; White v. Treat (C. C.) 100 Fed. 201; Sawmill Co. v. O'Shee, 111 La. 817, 35 South. 919.