249. What is the reason that the air is so cold on great heights? What is the relation of heat to the forms of substances? What is said of the melting of ice? What of the vaporization of water? State the general conclusion in regard to latent and sensible heat.
250. State in full what is said of latent heat in reference to clouds. Explain the operation of freezing mixtures.
251. State the examples of the production of cold by evaporation.
252. State and explain the experiment represented in Fig. 221.
253. Give the facts stated in regard to the degree of heat which man can endure. Give the reasons why the heat did not produce a greater effect in these cases.
254. What effect does heat produce upon the bulk of substances? What is said of water as an exception? Describe the process of freezing as illustrated by the diagram.
256. What would be the process if the exception did not exist? State what would be the results.
257. What would be the consequence if the freezing point were above 32°? What if it were below? What is said of the force of expansion in ice? What are some of the benefits which come from this expansion?
CHAPTER XIV.