Gold separates itself as money from the process of circulation whenever a commodity interrupts the process of its metamorphosis and remains in its form of a gold chrysalis. This occurs every time a sale is not immediately followed by purchase. The independent isolation of gold as money is, thus, a material expression of the disintegration of the process of circulation, or of the metamorphosis of commodities, into two separate acts independent of each other. The coin itself becomes money as soon as its course is interrupted. In the hands of the seller who takes it in exchange for his commodity, it is money and not coin; as soon as it passes out of his hands it is again coin. Everybody is a seller of the one commodity which he produces, but a buyer of all other commodities which he needs for his existence in society. While his selling is determined by the labor-time required for the production of his commodity, his buying is determined by the continual renewal of the wants of life. In order to be able to buy without having sold anything, he must sell without buying. In fact, the circulation process C―M―C is a dynamic unity of sale and purchase only in so far as it constitutes at the same time the constant process of its separation. In order that money should flow continuously as coin, coin must constantly coagulate as money. The continuous flow of coin depends on its constant accumulations in the form of reserve-funds of coin which spring up throughout the sphere of circulation and form sources of supply; the formation, distribution, disappearance, and reformation of these reserve funds is constantly changing, their existence constantly disappears, their disappearance constantly exists. Adam Smith expressed this never-ceasing transformation of coin into money and of money into coin by saying that every owner of commodities must always keep in supply besides the particular commodity which he sells, a certain quantity of the universal commodity with which he buys. We saw, that in the process C―M―C the second member M―C splits up into a series of purchases which do not take place at once, but at intervals of time, so that one part of M circulates as money while the other rests as money. Money is in that case only _suspended coin_ and the separate parts of the circulating mass of coins appear now in one form, now in another, constantly changing. This first transformation of the medium of circulation into money represents, therefore, but a technical aspect of money circulation.[90]