Every letter of attorney, or other instrument of writing containing a power to do any act or business whatever, other than the conveyance of real estate, as agent or attorney for another, may be acknowledged or proved and certified, in the same manner as deeds conveying or affecting real estate are, by law, required to be acknowledged or proved and certified, and, when so acknowledged or proved and certified, may, with the certificate of acknowledgment or proof, be read in evidence without further proof of the execution thereof.