46 CHEMISTRY OF FARM PRACTICE 



rivers, even in temperate zones, would freeze from bottom 

 to top into masses of ice which no summer sun would have 

 power to melt. Under these conditions the circulation of 

 water would be prevented and our latitudes would be well- 

 nigh uninhabitable. 



When water under atmospheric pressure is heated to 

 a temperature of 100 Centigrade, or 212 Fahrenheit, 

 it assumes the gaseous form, and is known as steam. 



41. Solvent Action of Water. Water is the most widely 

 distributed, and also the most important of solvents. It 

 not only dissolves plant food, but also serves as a medium 

 for its transportation from the soil to the plants. All of 

 the plant food that is derived from the soil is taken up 

 from solution; hence the solubility of the materials deter- 

 mines their availability as plant food. 



Water charged with carbonic acid gas is the most im- 

 portant natural solvent. In the decay of organic matter 

 in the soil a great deal of carbonic acid and some nitric 

 acid are liberated. This is one reason why it is desirable 

 to incorporate a large amount of organic matter in soil. 

 The nitric acid formed during the process of nitrification 

 is a stronger solvent than carbon dioxide; but the quantity 

 formed is comparatively small; hence the influence of 

 the carbon dioxide as a solvent in the soil is believed to 

 be greater than that of nitric acid. The nitric acid imme- 

 diately reacts with the basic elements in the soils, such as 

 calcium, sodium, potassium, magnesium, and ammonium, 

 producing metallic nitrates, all of which are soluble. In 

 this way, the plant may be furnished not only with nitrogen, 

 but with potassium or calcium as well. Phosphoric acid 

 and monocalcium phosphate are both soluble in pure 

 water. Dicalcium phosphate, when present in soil, is 

 insoluble in water, but it may be dissolved by treating 

 it with neutral ammonium citrate of a specific gravity of 

 1.09. Tricalcium phosphate is insoluble in water; but it 

 is soluble to some extent in the soil moisture when the 



