2. In order to preserve equality among the states, in their commercial relations, the constitution provides that " no tax or duty shall be laid on articles exported from any state." Art. 1, s. 9. And to prevent a pernicipus interference with the commerce of the nation, the 10th section of the 1st article of the constitution contains the following prohibition: " No state shall, without the consent of congress, lay any imposts or duties on imports or exports, except what may be absolutely necessary for executing its inspection laws; and the net produce of all duties and imposts, laid by any state on imports or exports, shall be for the use of the treasury of the United States; and all such laws shall be subject to the revision and control of the congress." Vide 12 Wheat. 419; and the article Importation.