A similar effect is produced in various branches of business by the more or less prolonged periods in which rather large quantities of raw material are thrown on the market. In London for example great auction sales of wool take place every three months, and the wool market is controlled by them. The cotton market on the other hand is on the whole restocked continuously, if not uniformly, from harvest to harvest. Such periods determine the principal dates when these raw materials are bought. Their effect is particularly great on speculative purchases necessitating advances for longer or shorter periods for these elements of production, just as the nature of the produced commodities acts on the speculative, intentional withholding of a product for a longer or shorter term in the form of potential commodity-capital. "The agriculturist must also be a speculator to a certain extent and therefore hold back the sale of his products if prevailing conditions so suggest . . . ." Here follow a few general rules. ". . . However in the sale of the products, it all depends mainly on the person, the product itself, and the locality. Anyone who, besides being skilful and lucky (!), is provided with sufficient working capital will not be blamed if for once he keeps his grain crop stored as long as a year when prices are unusually low. On the other hand a man who lacks working capital or is altogether devoid (!) of speculative spirit will try to get the current average prices and will be compelled to sell as soon and as often as opportunity presents itself. It will almost always mean a loss to keep wool stored longer than a year, while corn and oil seed may be stored for several years without detriment to their properties and high quality. Products generally subject to sever fluctuation at short intervals, for instance oil seed, hops, teasel and the like, may be stored to good advantage during years in which the selling price is far below the price of production. It is least permissible to postpone the sale of articles whose preservation involves daily expense, such as fatted cattle, or which are perishable, such as fruit, potatoes, etc. In various localities a certain product fetches its lowest average price in certain seasons, its highest in others. Thus, in some parts the average price of corn is lower around St. Martin's Day than between Christmas and Easter. Furthermore some products sell well in certain localities only at certain times, as is the case with wool in the wool markets of those localities where the wool trade at other times is dull, etc." (Kirchhof, p. 302.)In the study of the second half of the time of circulation, during which the money is reconverted into the elements of productive capital, it is not only this transformation, taken by itself, that should be given consideration, not only the time within which the money returns, according to the distance of the market in which the product is sold. What must also be considered, and primarily so, is the amount of that part of the advanced capital which is always to be available in the form of money, in the condition of money-capital.
Apart from all speculation, the volume of the purchases of those commodities which must always be available as a productive supply depends on the times of the renewal of this supply, hence on circumstances which in their turn are dependent on market conditions and which therefore are different for different raw materials. In these cases money must be advanced from time to time in rather large quantities and in lump sums. It returns more or less rapidly, but always in instalments, according to the turnover of capital. One portion of it, namely the part reconverted into wages, is just as continually expended again at short intervals. But another portion, namely that which is to be reconverted into raw material, etc., must be accumulated for rather long periods, as a reserve fund for either buying or paying. Therefore it exists in the form of money-capital, although the volume in which it exists as such, changes.
We shall see in the next chapter that other circumstances arising either from the process of production or that of circulation make it necessary for a certain portion of the advanced capital to be available in the form of money. In general it must be noted that the economists are very prone to forget not only that a part of the capital required in a business passes successively through the three stages of money-capital, productive capital, and commodity-capital, but also that different portions of it continuously and simultaneously possess these forms, although the relative magnitudes of these portions vary all the time. It is especially the part always available as money-capital that is forgotten by the economists, although precisely this circumstance is highly essential for an understanding of bourgeois economy and consequently makes its importance felt as such also in practice.