With grains thus turned into "homogeneous abstractions" (Cronon 1991, p. 132), disentangled at least partially from their heterogeneous physical reality, it was possible to enter into a contract to buy or to sell 5,000 bushels (the standard contract size) of, for example, "Chicago No. 2 white winter wheat" at a set price at a given future time. Such a contract had no link to any particular physical entity, and because its terms were standardized it was not connected permanently to those who had initially entered into it.

Donald MacKenzie, An Engine, Not a Camera, loc. 73