that of all and every kind of merchandise, whether pearls, precious stones, gold, silver, spices, and other objects and merchandise whatsoever, of whatever kind, name and sort, which may be bought, bartered, discovered, acquired and obtained within the limits of the said Admiralty, Your Highnesses grant from now henceforth to the said Don Cristóbal [Christopher Columbus] ... the tenth part of the whole, after deducting all the expenses which may be incurred therein