The inorganic matters in the soil can enter the plant only when dissolved in water. _Potash_, _soda_, _lime_, and _magnesia_, are soluble in their pure forms. Magnesia is injurious when present in too large quantities. _Sulphuric_ acid is often necessary as a manure, and is usually most available in the form of sulphate of lime or plaster. It is also valuable in its pure form to prevent the escape of ammonia from composts. _Phosphoric_ acid is highly important, from its frequent deficiency in worn-out soils. It is available only under certain conditions which will be described in the section on manures. _Silica_ is the base of common sand, and must be united to an alkali before it can be used by the plant, because it is insoluble except when so united. _Chlorine_ is a constituent of common salt (chloride of sodium), and from this source may be obtained in sufficient quantities for manurial purposes. [What is the difference between _per_oxide and _prot_oxide of iron? How must the food of plants be supplied? What takes place after it enters the plant? What name is given to the compounds thus formed? How are proximates divided? Which class constitutes the largest part of the plant? Of what are animals composed, and how do they obtain the materials from which to form their growth?] _Oxide of iron_ is iron rust. There are two oxides of iron, the _peroxide_ (red) and the _protoxide_ (black). The former is a fertilizer, and the latter poisons plants. _Oxide of manganese_ is often absent from the ashes of our cultivated plants. The food of plants, both organic and inorganic, must be supplied in certain proportions, and at the time when it is required. In the plant, this food undergoes such chemical changes as are necessary to growth. The compounds formed by these chemical combinations are called _proximates_. Proximates are of two classes, those not containing nitrogen, and those which do contain it. The first class constitute nearly the whole plant. The second class, although small in quantity, are of the greatest importance to the farmer, as from them all animal muscle is made. Animals, like plants, are composed of both organic and inorganic matter, and their bodies are obtained directly or indirectly from plants. [What parts of the animal belong to the first class of proximates? What to the second? What is necessary to the perfect development of animals? Why are seeds valuable for working animals? What other important use, in animal economy, have proximates of the first class? Under what circumstances is animal fat decomposed?] The first class of proximates in animals comprise the fat, and like tissues. The second class form the muscle, hair, gelatine of the bones, etc. In order that they may be perfectly developed, animals must eat both classes of proximates, and in the proportions required by their natures. They require the phosphate of lime and other inorganic food which exist in plants.