Elements in the estoppel: When A stands by while his right is being infringed by B the following circumstances must as a general rule be present in order that the estoppel may be raised against A: (1) B must be mistaken as to his own legal rights: if he is aware that he is infringing the rights of another, he takes the risk of those rights being asserted; (2) B must expend money, or do some act, on the faith of his mistaken belief: otherwise, he does not suffer by A 's subsequent assertion of his rights; (3) acquiescence is founded on conduct with a knowledge of one 's legal rights, and hence A must know of his own rights; (4) A must know of B 's mistaken belief; with that knowledge it is inequitable for him to keep alliance and allow B to proceed on his mistake; (5) A must encourage B in his expenditure of money or other act, either directly or by abstaining from asserting his legal right.