Capital 2, subtitled The Process of Circulation of Capital, was prepared by Friedrich Engels from notes left by Marx & published in 1885. It's divided into three parts: The Metamorphoses of Capital & Their Circuits, The Turnover of Capital, & The Reproduction & Circulation of the Aggregate Social Capital. Here the main ideas behind the marketplace are to be found: how value & surplus-value are realized. Its dramatis personae, not so much the worker & the industrialist as in Volume 1, but rather the money owner & lender, the wholesale merchant, the trader & the entrepreneur or 'functioning capitalist.' Moreover, workers appear in Volume 2, essentially as buyers of consumer goods &, therefore, as sellers of the commodity labor power, rather than producers of value & surplus-value (altho, this latter quality, established in Volume 1, remains the solid foundation on which the whole of the unfolding analysis is based). Reading Volume 2 is of great significance to understanding the theoretical construction of Marx' whole argument. Marx himself precisely clarified this place, in a letter sent to Engels on 4/30/1868: 'In Book 1...we content ourselves with the assumption that if in the self-expansion process £100 becomes £110, the latter will find already in existence in the market the elements into which it will change once more. But now we investigate the conditions under which these elements are found at hand, namely the social intertwining of the different capitals, of the component parts of capital & of revenue (=s).' This intertwining, conceived as a movement of commodities & of money, enabled Marx to work out at least the essential elements, if not the definitive form of a coherent theory of the trade cycle, based upon the inevitability of periodic disequilibrium between supply & demand under the capitalist mode of production (Mandel, 1978, Intro to Vol. 2 of Capital). Volume 2 has indeed been not only a 'sealed book', but also a forgotten one. To a large extent, it remains so to this day. Part 3 is the point of departure for a topic given its Marxist treatment later in detail by Rosa Luxemburg etc.