Another large portion of capital, however, consists in instruments of production, of a more or less permanent character; which produce their effect not by being parted with, but by being kept; and the efficacy of which is not exhausted by a single use. To this class belong buildings, machinery, and all or most things known by the name of implements or tools. The durability of some of these is considerable, and their function as productive instruments is prolonged through many repetitions of the productive operation. In this class must likewise be included capital sunk (as the expression is) in permanent improvements of land. So also the capital expended once for all, in the commencement of an undertaking, to prepare the way for subsequent operations: the expense of opening a mine, for example; of cutting canals, of making roads or docks. Other examples might be added, but these are sufficient. Capital which exists in any of these durable shapes, and the return to which is spread over a period of corresponding duration, is called Fixed Capital. Of fixed capital, some kinds require to be occasionally or periodically renewed. Such are all implements and buildings: they require, at intervals, partial renewal by means of repairs, and are at last entirely worn out. In other cases the capital does not, unless as a consequence of some unusual accident, require entire renewal. A dock or a canal, once made, does not require, like a machine, to be made again, unless purposely destroyed. The most permanent of all kinds of fixed capital is that employed in giving increased productiveness to a natural agent, such as land. To return to the theoretical distinction between fixed and circulating capital. Since all wealth which is destined to be employed for reproduction comes within the designation of capital, there are parts of capital which do not agree with the definition of either species of it; for instance, the stock of finished goods which a manufacturer or dealer at any time possesses unsold in his warehouses. But this, though capital as to its destination, is not yet capital in actual exercise; it is not engaged in production, but has first to be sold or exchanged, that is, converted into an equivalent value of some other commodities, and therefore is not yet either fixed or circulating capital, but will become either one or the other, or be eventually divided between them. § 2. Increase of Fixed Capital, when, at the Expense of Circulating, might be Detrimental to the Laborers.