This section is from the book "Popular Law Library Vol7 Equity Jurisprudence, Trusts, Equity Pleading", by Albert H. Putney. Also available from Amazon: Popular Law-Dictionary.
"Where one person has a clear right to resort to two funds, and another person has a right to resort to but one of them, the latter may compel the former, as double creditor, to exhaust the fund on which the latter, as a simple creditor, has no claim." 12
In the case of Webb vs. Smith,13 the court explained this doctrine as follows:
"If A has a charge upon Whiteacre and Black-acre, and if B also has a charge upon Blackacre, only,
A must take payment of his charge out of Wniteacre, and must leave Blackacre so that B, the other creditor, may follow it, and obtain payment of his debt out of it. In other words, if two estates (Whiteacre and Black-acre) are mortgaged to one person, and subsequently one of them (Blackacre) is mortgaged to another person, unless Blackacre is sufficient to pay both charges, the first mortgagee will be compelled to take satisfaction out of Whiteacre, in order to leave Black-acre to the second mortgagee upon which alone he can go."