dS CHEMISTR Y FOR A GRICUL TURAL S TU DENTS 



(>T^. Point out how the great heat capacity of water renders (i) the climate 

 of Great Britain temperate, (2) a wet soil cold, and (3) a damp 

 room chilly. 



64. Point out the relation of heat to change of state, both from a liquid to 



a solid and a gas, and from a solid and a gas to a liquid. Explain 

 the difference of temperature exhibited by a wet and dry bulb 

 thermometer. Why does a mixture of salt and snow act as a freez- 

 ing mixture ? 



65. Point out how the high latent heat of vaporisation possessed by water 



helps to render (i) the climate of Great Britain temperate, (2) a wet 

 soil cold, and (3) a damp room chilly. Explain why the high latent 

 heat of liquefaction of ice gives rise to a raw, cold feeling during a 

 thaw. 



66. What is meant by the terms *' athermanous" and " diathermanous " ? 



How does the athermancy of water vapour affect the climate of 

 Great Britain ? 



67. Describe the effect of heating and cooling water upon its volume. 



Point out how these changes in volume can be utilised in the heat- 

 ing of buildings. It is stated that the water in a deep pond whose 

 surface is frozen rarely sinks below 4° C. Explain this. Account 

 for the useful effect of a hard frost upon the soil. 



68. Compare the use of alcohol and mercury in the construction of ther- 



mometers, taking into account their difference in specific heat, 

 boiling point, freezing point, co-efficient of expansion, and thermal 

 conductivity. 



Composition of Water. 



69. Describe fully the experiments which showed that water was a com- 



pound of hydrogen. State what change took place in (i) the iron 

 filings, (2) the steam. 



70. Describe the experiment which established the composition of water 



by synthesis, and state how the liquid produced was identified as 

 water. 



71. Before a jet of hydrogen is ignited, what precaution must be taken 



to ensure its purity ? Why should hydrogen and air constitute an 

 explosive mixture ? 



72. What do you mean by a "permanent" gas? 



']Tf. Two methods have now been employed to decompose chemical 

 compounds. What are they ? Illustrate your answer by examples. 

 *74. Identify the two gase<? (hydrogen, and either oxygen, nitrogen, or 

 carbonic acid gas). 



