Even if simple reproduction is assumed, a portion of the surplus-value must therefore always exist in the form of money and not of products, because otherwise it could not be converted for purposes of consumption from money into products. This conversion of the surplus-value from its original commodity-form into money must be further analysed at this place. In order to simplify the matter, we shall presuppose the most elementary form of the problem, namely the exclusive circulation of metal coin, of money which is a real equivalent.
According to the laws of the simple circulation of commodities (developed in Buch I, Kap. III), [English edition: Ch. III. -- Ed .]
the mass of the metal coin existing in a country must not only be sufficient to circulate the commodities, but must also suffice to meet the currency fluctuations, which arise partly from fluctuations in the velocity of the circulation, partly from a change in the prices of commodities, partly from the various and varying proportions in which the money functions as a medium of payment or as a medium of circulation proper. The proportion in which the existing quantity of money is split into a hoard and money in circulation varies continually, but the total quantity of money is always equal to the sum of the money hoarded and the money circulating. This quantity of money (quantity of precious metal) is a gradually accumulated hoard of society. Since a portion of this hoard is consumed by wear and tear, it must be replaced annually, the same as any other product. This takes place in reality by a direct or indirect exchange of a part of the annual product of a particular country for the product of countries producing gold and silver. However, this international character of the transaction conceals its simple course. In order to reduce the problem to its simplest and most lucid expression, it must be assumed that the production of gold and silver takes place in that particular country itself, that therefore the production of gold and silver constitutes a part of the total social production within every country.
Apart from the gold and silver produced for articles of luxury, the minimum of their annual production must be equal to the wear of metal coin annually occasioned by the circulation of money. Furthermore, if the sum of the values of the annually produced and circulating quantity of commodities increases, the annual production of gold and silver must likewise increase, inasmuch as the increased sum of values of the circulating commodities and the quantity of money required for their circulation (and the corresponding formation of a hoard) are not made good by a greater velocity of money currency and a more comprehensive function of money as a medium of payment, i.e., by a greater mutual balancing of purchases and sales without the intervention of actual money.
A portion of the social labour-power and a portion of the social means of production must therefore be expended annually in the production of gold and silver.
The capitalists who are engaged in the production of gold and silver and who, according to our assumption of simple reproduction, carry on their production only within the bounds of the annual average wear and tear and the annual average consumption of gold and silver entailed thereby throw their surplus-value -- which they consume annually, according to our assumption, with-out capitalising any of it -- directly into circulation in the money-form, which is its natural form; unlike the other branches of production, where it is the converted form of the product.
Furthermore, as far as wages are concerned -- the money-form in which the variable capital is advanced -- they are also not replaced by the sale of the product, by its conversion into money, but by a product itself whose natural form is from the outset that of money.
Finally the same applies also to that portion of the product of precious metals which is equal to the value of the periodically consumed constant capital, both the constant circulating and constant fixed capital consumed during the year.
Let us consider the circuit, or turnover, of the capital invested in the production of precious metals first in the form of M---C . . . P. . . M'. Since C in M---C consists not only of labour-power and means of production but also of fixed capital, only a part of whose value is consumed in P, it is evident that M', the product, is a sum of money equal to the variable capital laid out in wages plus the circulating constant capital laid out in means of production plus a portion of the value equivalent to the worn-out fixed capital plus the surplus-value. If the sum were smaller, the general value of gold remaining the same, then the mine would be unproductive or, if this got to be generally the case, the value of gold compared with the value of commodities that remains unchanged would subsequently rise;i.e., the prices of commodities would fall, so that henceforth the amount of money laid out in M---C would be smaller.