What is the test for a mortgage where after acquired lands are fully and specifically described as a subject of the mortgage?

MacKeigan C.J.N.S. said the following at p. 21: I should emphasize that even if after-acquired lands are fully and specifically described in a purported mortgage, a legal mortgage does not result but at most an equitable charge enforceable between the parties and not against a subsequent purchaser as in the present case. Chief Justice Strong in Imrie v. Archibald et al. said (pp. 387-88): Apart from the common law doctrine of estoppel however, if there had been an unambiguous specific description of property as a subject of the mortgage to which the mortgagor had no title at the date of the mortgage but had afterwards acquired a title, a court of equity would no doubt under ordinary circumstances have interfered (except as against a bona fide purchaser for value without notice of the equity of redemption) in favour of the mortgagees to charge such after acquired lands with the mortgage debt, but the answer to any argument founded on that doctrine is conclusive from what I have already mentioned that no intention is indicated to include such after acquired property by the general words used... Without adequate identification of the property to be charged, however, neither a legal mortgage nor an enforceable equitable charge can be put on property, either present or future.