VAKIOUS KINDS OF MANURE. 121 



formed. Phosphate of lime exists abundantly in animal tissues ; and 

 hence it must be furnished by plants. The use of bone-dust as a 

 manure, depends in a great measure on the phosphate of lime which 

 it contains. Besides phosphate of lime, bones contain about 3 per 

 cent, of phosphate of magnesia, carbonate of lime, and salts of soda. 

 The gelatine of bones also seems to act beneficially, by forming car- 

 bonic acid and ammonia. Bones are best applied mixed with sulphuric 

 acid, so as to give rise to the formation of soluble phosphates by de- 

 composition. They are broken into pieces, and mixed with half their 

 weight of boiling water, and then with half their weight of sulphuric 

 acid. The mixture is applied to the soil, either in a dry state by 

 the drill, with saw-dust and charcoal added, or in a liquid state diluted 

 with 100 to 200 waters. Phosphates and other inorganic matters, 

 sometimes exist potentially in the soil, but in a dormant state, re- 

 quiring the addition of something to render them soluble. Allowing 

 the ground to lie fallow, and stirring and pulverizing it, are methods 

 by which air and moisture are admitted, and time is allowed for the 

 decomposition of the materials, which are thus rendered available for 

 plants. Sulphur exists in considerable quantity in some plants, as 

 Cruciferse, and it forms an element in albumen ; hence the use of 

 sulphuric acid and of sulphates as manures. Sulphate of lime or 

 gypsum, is well fitted as a manure for clover. It acts in supplying 

 sulphur and lime, and in absorbing ammonia. Charcoal in a solid 

 state, has been applied with advantage as a manure. It acts partly 

 by taking up ammonia in large quantities, and partly in combining 

 slowly with oxygen, so as to form carbonic acid. The effects of car- 

 bonic acid on vegetation are said to be remarkably conspicuous in 

 some volcanic countries, in which this gas is evolved from the bottom 

 of lakes. When it accumulates in large qxiantities, however, it destroys 

 plants as well as animals. 



247. manuring with Oreen Crops is sometimes practised. The 

 mode adopted is to sow certain green crops, the roots of which extend 

 deeply into the soil; and when the plants have advanced considerably 

 in growth, to plough them in, and sow a crop of some kind of grain. 

 In this way the nutritive matter from the deeper part of the soil is 

 brought within reach of the roots of the grain crop. Manuring with 

 sea-weeds is also resorted to in cases where they are accessible. They 

 supply abundance of carbonate, phosphate, and sulphate of lime, besides 

 chloride of sodium. There are considerable differences in their chemical 

 composition; thus, while in Laminaria saccharina, alkaline carbonates, 

 potash, and iodine, predominate ; in Fucus vesiculosus and serratus, 

 sulphates and soda are in excess, and iodine is less abundant. In the 

 cultivation of the Coco-nut Palm, Mr. M'Nab finds that sea-weeds act 

 very beneficially. 



248. Liquid manures have of late years been much employed, and 



