§ 507. Condemnation certificate of commissioner. The power of condemnation shall not be exercised by a housing company, except with the authorization of such action by the commissioner, which authorization shall be in the form of a certificate declaring that the acquisition of the property is necessary for the construction of a project and that the acquisition is in the public interest and necessary for the public use. Such certificate shall be issued only after a public hearing. The certificate shall state the nature of the interest to be acquired.