The circulating capital entering into the process of production transfers its entire value to the product and must therefore be continually replaced in kind by the sale of the product, if the process of production is to proceed without interruption. The fixed capital entering into the process of production transfers only a part of its value (the wear and tear) to the product and despite this wear and tear continues functioning in the process of production. Therefore it need not be replaced in kind until the lapse of intervals of various duration, at any rate not as frequently as the circulating capital. This necessity of replacement, the reproduction term, is not only quantitatively different for the various constituent parts of fixed capital, but, as we have seen, a part of the perennial fixed capital, that which lasts longer, may be replaced annually or at shorter intervals and added in kind to the old fixed capital. In the case of fixed capital of different properties the replacement can take place only all at once at the end of its period of durability. It is therefore necessary to reduce the specific turnovers of the various parts of fixed capital to a homogeneous form of turnover, so that they will remain different only quantitatively, namely, according to duration of turnover. The qualitative identity does not come about if we take as our starting-point P ... P, the form of the continuous process of production. For definite elements of P must be constantly replaced in kind while others need not. However the form M ... M' undoubtedly yields this identity of turnover. Take for instance a machine worth 10,000, which lasts ten years of which one-tenth, or 1,000, is annually reconverted into money. These 1,000 have been converted in the course of one year from money-capital into productive capital and commodity-capital, and then reconverted from this into money-capital. They have returned to their original form, the money-form, just like the circulating capital, if we study the latter in this form, and it is immaterial whether this money-capital of 1,000 is once more converted at the end of the year into the bodily form of a machine or not. In calculating the aggregate turnover of the advanced productive capital we therefore fix all its elements in the money-form, so that the return to that form concludes the turnover. We assume that value is always advanced in money, even in the continuous process of production, where this money-form of value is only that of money of account. Thus we can compute the average. Suppose the fixed capital is 80,000 and its period of reproduction 10 years, so that 8,000 of it annually return to their money-form, or it completes one-tenth of its turnover. Suppose further the circulating capital is 20,000, and its turnover is completed five times per year. The total capital would then be 100,000. The turned-over fixed capital is 8,000, the turned-over circulating capital five times 20,000, or 100,000. Then the capital turned over during one year is 108,000, or 8,000 more than the advanced capital. 1 + 2/25 of the capital have been turned over. In the illustration under No. 3, then, the sums assumedly returned into the hands of the capitalist at the end of one year are (a) a sum of value amounting to 20,000 which he invests again in the circulating constituents of the capital, and (b) a sum of 8,000 which has been set free by wear and tear from the value of the advanced fixed capital; simultaneously this same fixed capital remains in the process of production, but with the reduced value of 72,000 instead of 80,000. The process of production therefore would have to be continued for nine years more, before the advanced fixed capital outlived its term and ceased to function as a creator of products and values, so that it would have to be replaced. The advanced capital-value, then, has to pass through a cycle of turnovers, in the present case a cycle of ten annual ones, and this cycle is determined by the life, hence the reproduction or turnover time of the applied fixed capital. As the magnitude of the value and the durability of the applied fixed capital develop with the development of the capitalist mode of production, the lifetime of industry and of industrial capital lengthens in each particular field of investment to a period of many years, say of ten years on an average. Whereas the development of fixed capital extends the length of this life on the one hand it is shortened on the other by the continuous revolution in the means of production, which likewise incessantly gains momentum with the development of the capitalist mode of production. This involves a change in the means of production and the necessity of their constant replacement, on account of moral depreciation, long before they expire physically. One may assume that in the essential branches of modern industry this life-cycle now averages ten years. However we are not concerned here with the exact figure. This much is evident: the cycle of interconnected turnovers embracing a number of years, in which capital is held fast by its fixed constituent part, furnishes a material basis for the periodic crises. During this cycle business undergoes successive periods of depression, medium activity, precipitancy, crisis. True, periods in which capital is invested differ greatly and far from coincide in time. But a crisis always forms the starting-point of large new investments. Therefore, from the point of view of society as a whole, more or less, a new material basis for the next turnover cycle.[22a] The same Scrope says in the same passage: Scrope confuses here the difference in the flow of certain parts of the circulating capital, brought about for the individual capitalist by terms of payment and conditions of credit, with the difference in the turnovers due to the nature of capital. He says that wages must be paid weekly out of the weekly receipts from paid sales or bills. It must be noted here in the first place that certain differences occur relative to wages themselves, depending on the length of the term of payment, that is, the length of time for which the labourer must give credit to the capitalist, whether wages are payable every week, month, three months, six months, etc. In this case, the law expounded before, holds good, to the effect that the quantity of the means of payment required for all periodical payments (hence of the money-capital to be advanced at one time) is in inverse [This is evidently a slip of the pen, the proportion being direct and not inverse. Ed.] proportion to the length of their periods. (Buch I, Kap. III, 3b, Seite 124.) [English edition: Ch. III, 3b, p. 141. Ed.] In the second place, it is not only the new value added in the process of production by the week s labour which enters completely into the weekly product, but also the value of the raw and auxiliary materials consumed by the weekly product. This value circulates with the product containing it. It assumes the form of money through the sale of the product and must be reconverted into the same elements of production. This applies as much to the labour-power as to the raw and auxiliary materials. But we have already seen (Chapter VI, II, 1) that continuity of production requires a supply of means of production different for different branches of industry, and different within one and the same branch of business for different component parts of this element of the circulating capital, for instance, for coal and cotton. Hence, although these materials must be continually replaced in kind, they need not always be bought anew. The frequency of purchases depends on the size of the available stock, on the time it takes to exhaust it. In the case of labour-power there is no such storing of a supply. The reconversion into money of the part of capital laid out in labour-power goes hand in hand with that of the capital invested in raw and auxiliary materials. But the reconversion of the money, on the one hand into labour-power, on the other into raw materials, proceeds separately on account of the special terms of purchase and payment of these two constituents, one of them being bought as a productive supply for long periods, the other, labour-power, for shorter periods, for instance a week. On the other hand the capitalist must keep a stock of finished commodities besides a stock of materials for production. Let us leave sales difficulties aside. A certain quantity of goods must be produced, say, on order. While the last portion of this lot is being produced, the finished products are waiting in the warehouse until the order can be completely filled. Other differences in the turnover of circulating capital arise whenever some of its separate elements must stay in some preliminary stage of the process of production (drying of wood, etc.) longer than others. The credit system, to which Scrope here refers, as well as commercial capital, modifies the turnover for the individual capitalist. On a social scale it modifies the turnover only in so far as it does not accelerate merely production but also consumption.
Economic Manuscripts: Capital: Volume Two