46 CHEMISTRY FOR AGRICULTURAL STUDENTS 



Aqueous Vapour, Water, and Ice. 



35. What is meant by "deliquescence," and to what is it due? Name 



two substances that commonly exhibit this phenomenon. 



36. What are the " three states of matter," and what is meant by " change 



of state"? 



37. What do you understand by " temperature"? Name the instrument 



used for measuring temperature, and describe its construction and 

 action. Why can water not be employed instead of mercury or 

 alcohol in its construction? (See Study VIII.) 



38. What is meant by the " boiUng point " and "freezing point " ? Why, 



in the determination of the former, must the atmospheric pressure 

 be taken into account ? 



39. Into what number of degrees are the Fahrenheit and centigrade scales 



of temperature divided, and what is taken as the zero for each 



scale ? What fraction of a degree centigrade is a degree Fahrenheit ? 



Calculate 15° C. into degrees Fahrenheit, and 20° F. into degrees 



centigrade. 

 *40. Determine the boiling point of the liquid. 

 *4i. Is the zero point of the centigrade thermometer correct ? 



Water as a Solvent. 



42. What is meant by the terms solubility and insolubility? Illustrate 



your answer by examples of solids, liquids, and gases. When is a 

 solution said to be saturated ? 



43. What is the usual effect of rise in temperature upon the solubility of 



(i) a solid, (2) a gas? Trace the relation between this and the 

 effect of temperature upon change of state of solids and gases. 



44. Explain distillation with reference to change of state. How may dis- 



tillation be employed to produce pure water from water containing 

 solid and gaseous impurities ? 



45. Why does evaporation of water take place at temperatures below the 



boiling point? Will evaporation from the soil take place more 

 rapidly in dry weather or damp, warm weather or cold ? 



46. If the air be saturated with water vapour, what takes place if the 



temperature falls? What is meant by the "dew point"? Why 

 does the wet bulb thermometer read lower than the dry except 

 when the air is saturated with water vapour ? 



47. Give an account of the distillation of water that takes place in nature ; 



trace the history of water from the point at which it is evaporated 

 from land or sea, through its existence as rain, spring, river, and 

 sea water, with especial reference to the gaseous and solid sub- 

 stances it dissolves. 



