According to Sec. 18 of the Partnership Act, each partner is the agent of his co-partners for the purpose of contracting debts and obligations in the usual course of partnership business. 

Each partner is praepositus negotis societatis, and may consequently bind all the other partners by his acts in all matters which are within the scope and objects of the partnership. 

The agency operates against dormant or sleeping partners as well, they too are liable for the acts of acting or ostensible partners.