In that acceptation, value is usually divided into value-in-use, and value-in-exchange. Certain esteemed qualities of an object may make it of great value-in-use; but unless its acquisition demand sacrifice, it can have no value-in-exchange. It is only with this class of value that economists deal. No matter how important the intrinsic qualities of any article may be, if there be no limitation of its quantity and its acquisition requires no sacrifice, it can have no value in the sense in which the word "value" is used in political economy. The air has qualities inestimable to mankind; it must be regarded as incomparably the most useful of all the objects of human desire; yet it has no value because there is no limitation of its quantity. By reason of its universality and accessibility, air requires no sacrifice to get it. If, however, circumstances should render air limited in quantity it is conceivable that it might become of surpassing value. A man confined in the "Black Hole" of Calcutta would give a fortune for free access to air. So water, where freely obtainable, without sacrifice, although indispensable to life, has no value in the economic sense--no value in exchange. But when not so obtainable, as in populous cities, where sacrifice of time and labor would be necessary to obtain it from river, lake, or spring, people pay for the convenience of having it in their homes. The indispensable prerequisites of value in all objects are utility--either actual or attributed--combined with limitation of quantity and the sacrifice necessary to be made in order to obtain it. But value is not a property inhering in any article itself. It is not intrinsic. If the value were inherent or intrinsic it could not be taken away. To illustrate: A generation ago the cradle with which wheat was harvested was said to possess intrinsic value. It was undoubtedly one of the most useful of all the articles needed by man. All that was then in that machine is in it still, yet the value is gone. Had the value been something that was intrinsic, had it resided in the object, and not in the mind, that cradle would still be worth all that it ever was. So, on the other hand, an article may possess most estimable qualities, but if those qualities are not known or recognized by the human mind the article will have no value. A few years ago cotton seed had no value as an article of general commerce. To-day it is exceedingly valuable, because it has been found to possess estimable qualities not before suspected.