“ When one commodity replaces another, the money-commodity always sticks to the hands of some third person. ”
 Karl Marx, Das Kapital (1885). copy citation

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“that, though the money-form of any definite quantity of commodities is only transient within the sphere of circulation, still the money transiently in the hands of one man during the metamorphosis of a certain commodity necessarily passes into the hands of another, so that in the first instance commodities are not only exchanged all-sidedly, or replace one another, but this replacement is promoted and accompanied by an all-sided precipitation of money. “When one commodity replaces another, the money-commodity always sticks to the hands of some third person. Circulation sweats money from every pore.” (Buch I, S. 92.) [English edition: p. 113. — Ed.] The same identical fact is expressed, on the basis of the capitalist production of commodities, by a portion of capital constantly existing in the form of money-capital, and a portion of surplus-value constantly being found in the hands of its owners, likewise in the form of money.” source