58 AGRICULTURAL CHEMISTRY 



tion is obtained. The particles of the material are sepa- 

 rated in the process of solution, and every part of the so- 

 lution, even though dilute, contains some of the dissolved 

 substance. When a substance is dissolved, ions are pro- 

 duced. They are small masses of the material that have 

 undergone changes due to the action of the solvent. The 

 ions possess definite electrical properties. When a sub- 

 stance goes into solution, the process is both physical and 

 chemical. In some cases a change of temperature occurs, 

 as when ammonium nitrate solution is made. 



16, Water of Crystallization. Many substances con- 

 tain, in chemical combination, water necessary for the 

 formation of crystals. This is what is meant by water 

 of crystallization. Without this water, crystals could 

 not be formed. The amount of water required bears a 

 definite relation to the composition of the crystals. When 

 copper sulfate crystallizes, 7 molecules of water of crys- 

 tallization are added to the substance. In purchasing 

 some substances, as sulfate of soda, a large amount of 

 water is obtained, as this compound contains 10 molecules 

 of water of crystallization. When the substance is heated 

 in an oven, to a sufficiently high temperature, usually 

 above 100 C., the water of crystallization is expelled and 

 the anhydrous substance is obtained. Water of crystal- 

 lization is entirely different from hydroscopic moisture or 

 moisture which is absorbed from the air. Some chem- 

 ical compounds, when exposed to the air, give up their 

 water of crystallization. Such substances are called 

 efflorescent. Other compounds, as KOH and CaCl 2 , ab- 



