A Person shall not be capable of acting as a Guardian, except in administering the following Declaration, until he have made and subscribed before One of the Guardians a Declaration to the Effect following:

”I A.B. of do solemnly declare that I will faithfully and impartially, according to the best of my Skill and Judgement, execute all the Powers and Authorities reposed in me as One of the Guardians incorporated by the Name of “The Guardians of the Birmingham Proof House” by virtue of “The Gun Barrel Proof Act 1868,” and also that I [here set forth a Statement of the Qualification required by this Act in the Terms thereof].’