The statute (P. L., c. 66, s. 25) requires the purchaser of real estate sold by a tax collector to give notice to mortgagees within thirty days from the sale, and the sale “shall be void as against any mortgagee to whom such notice” is not given. The requirement of notice within the time specified is a material condition “because the statute makes it so.” Derry Bank v. Griffin, 68 N. H. 183, 184. The principle that in all cases of sales of real estate for non-payment of taxes “every prerequisite to the exercise of the power must precede its exercise” (Cahoon v. Coe, 57 N. H. 556, 569) extends to matters to be performed in order that a sale include a mortgage interest, and the statutory regulations are fixed and rigid.

Decree for defendant.