§ 6 — Partners bound by acts on behalf of firm

6. An act or instrument relating to the business of the firm and done or executed in the firm-name, or in any other manner showing an intention to bind the firm, by any person thereto authorised whether a partner or not, is binding on the firm and all the partners:Provided that this section shall not affect any general rule of law relating to the execution of deeds or negotiable instruments.