In compliance with a resolution of the House of Representatives adopted at their last session, instructions have been given to all the ministers of the United States accredited to the powers of Europe and America to propose the proscription of the African slave trade by classing it under the denomination, and inflicting on its perpetrators the punishment, of piracy. Should this proposal be acceded to, it is not doubted that this odious and criminal practice will be promptly and entirely suppressed. It is earnestly hoped that it will be acceded to, from the firm belief that it is the most effectual expedient that can be adopted for the purpose. At the commencement of the recent war between France and Spain it was declared by the French Government that it would grant no commissions to privateers, and that neither the commerce of Spain herself nor of neutral nations should be molested by the naval force of France, except in the breach of a lawful blockade. This declaration, which appears to have been faithfully carried into effect, concurring with principles proclaimed and cherished by the United States from the first establishment of their independence, suggested the hope that the time had arrived when the proposal for adopting it as a permanent and invariable rule in all future maritime wars might meet the favorable consideration of the great European powers. Instructions have accordingly been given to our ministers with France, Russia, and Great Britain to make those proposals to their respective Governments, and when the friends of humanity reflect on the essential amelioration to the condition of the human race which would result from the abolition of private war on the sea and on the great facility by which it might be accomplished, requiring only the consent of a few sovereigns, an earnest hope is indulged that these overtures will meet with an attention animated by the spirit in which they were made, and that they will ultimately be successful. The ministers who were appointed to the Republics of Colombia and Buenos Ayres during the last session of Congress proceeded shortly afterwards to their destinations. Of their arrival there official intelligence has not yet been received. The minister appointed to the Republic of Chile will sail in a few days. An early appointment will also be made to Mexico. A minister has been received from Colombia, and the other Governments have been informed that ministers, or diplomatic agents of inferior grade, would be received from each, accordingly as they might prefer the one or the other.