New York Consolidated Laws, Real Property Law - RPP § 320. Certain deeds deemed mortgages

A deed conveying real property, which, by any other written instrument, appears to be intended only as a security in the nature of a mortgage, although an absolute conveyance in terms, must be considered a mortgage;  and the person for whose benefit such deed is made, derives no advantage from the recording thereof, unless every writing, operating as a defeasance of the same, or explanatory of its being desired to have the effect only of a mortgage, or conditional deed, is also recorded therewith, and at the same time.