What is the first of these? The second? Third? Fourth? Do all mineral manures possess all of these qualities?] The second class of manures named in the general division of the subject, in the early part of this chapter, comprises those of a mineral character, or _inorganic_ manures. These manures have four kinds of action when applied to the soil. 1st. They furnish food for the inorganic part of plants. 2d. They prepare matters already in the soil, for assimilation by roots. 3d. They improve the mechanical condition of the soil. 4th. They absorb ammonia. Some of the mineral manures produce in the soil only one of these effects, and others are efficient in two or all of them. The principles to be considered in the use of mineral manures are essentially given in the first two sections of this book. It may be well, however, to repeat them briefly in this connection, and to give the _reasons_ why any of these manures are needed, from which we may learn what rules are to be observed in their application. [Relate what you know of the properties of vegetable ashes? How does this relate to the fertility of the soil? According to what two rules may we apply mineral manures? What course would you pursue to raise potatoes on a soil containing a very little phosphoric acid and no potash?] 1st. Those which are used as food by plants. It will be recollected that the _ash_ left after burning plants, and which formed a part of their structures, has a certain chemical composition; that is, it consists of alkalies, acids, and neutrals. It was also stated that the ashes of plants of the same kind are always of about the same composition, while the ashes of different kinds of plants may vary materially. Different parts of the same plant too, as we learned, are supplied with different kinds of ash. For instance, _clover_, on being burned, leaves an ash containing _lime_, as one of its principal ingredients, while the ash of _potatoes_ contains more of _potash_ than of any thing else. In the second section (on soils), we learned that some soils contain every thing necessary to make the ashes of all plants, and in sufficient quantity to supply what is required, while other soils are either entirely deficient in one or more ingredients, or contain so little of them that they are unfertile for certain plants. [Would you manure it in the same way for wheat? Why?]