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 peroxide and protoxide 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?