I do not say that these are the only ingredients of any value in a ton of manure. Nearly all the other ingredients are indispensable to the growth of plants, and if we should use manures containing nothing but nitrogen, phosphoric acid, and potash, the time would come when the crops would fail, from lack of a sufficient quantity of, perhaps, magnesia, or lime, sulphuric acid, or soluble silica, or iron. But it is not necessary to make provision for such a contingency. It would be a very exceptional case. Farmers who depend mainly on barn-yard manure, or on plowing under green crops for keeping up the fertility of the land, may safely calculate that the value of the manure is in proportion to the amount of nitrogen, phosphoric acid, and potash, it contains. We draw out a ton of fresh manure and spread it on the land, therefore, in order to furnish the growing crops with 12¾ lbs. of nitrogen, 6½ lbs. of phosphoric acid, and 13½ lbs. of potash. Less than 33 lbs. in all! We cannot dispense with farm-yard manure. We can seldom buy nitrogen, phosphoric acid, and potash, as cheaply as we can get them in home-made manures. But we should clearly understand the fact that we draw out 2,000 lbs. of matter in order to get 33 lbs. of these fertilizing ingredients. We should _try to make richer manure_. A ton of manure containing 60 lbs. of nitrogen, phosphoric acid, and potash, costs no more to draw out and spread, than a ton containing only 30 lbs., and it would be worth nearly or quite double the money. How to make richer manure we will not discuss at this time. It is a question of food. But it is worth while to enquire if we can not take such manure as we have, and reduce its weight and bulk without losing any of its nitrogen, phosphoric acid, and potash. CHAPTER XIV. FERMENTING MANURE. Dr. Vœlcker placed 2,838 lbs. of fresh mixed manure in a heap Nov. 3, 1854, and the next spring, April 30, it weighed 2,026 lbs., a shrinkage in weight of 28.6 per cent. In other words 100 tons of such manure would be reduced to less than 71½ tons. The heap was weighed again, August 23d, and contained 1,994 lbs. It was again weighed Nov. 15, and contained 1,974 lbs. The following table shows the composition of the heap when first put up, and also at the three subsequent periods: Table Showing Composition of the Whole Heap; Fresh Farm-Yard Manure (No. I.) Exposed--Expressed in Lbs.