The principal shall have advantage of his agent’s contracts in the same manner as he shall be bound by them, so far as they come within the scope of his agency. If, however, the agency shall have been concealed, the party dealing with him may set up any defense against the principal which he has against the agent.
§ 2204; Civil Code 1895, § 3032; Civil Code 1910, § 3604; Code 1933, § 4-313.