QUANTITY AND TRANSMISSION OF HEAT 141 



* * 



of cold water. Heat the upper part of the tube with a 

 Bunsen burner as shown in Figure 121. The water at 



the upper part of the tube 

 may be boiled for some time 

 without melting the ice. 



Experiment 45. Place the bulb 

 of an air thermometer a fraction 

 of an inch below the surface of the 

 water in a funnel arranged as in 

 Figure 122. Now pour some ether 



FIG. 121. -Water is a poor con- on the water and Se1 j Jt on fire ' 

 ductor of heat, as is shown by the Hardly any change in tempera- 

 ex P 3riment. ture win be indicated by the air 



thermometer. The conductivity of water is about 'y*W that of 

 silver. 



Gases are even poorer conductors than liquids. Dry 

 air has almost no conductivity. The warmth of fur 

 and woolen garments is due to 

 the fact that they have so many 

 minute spaces containing non-con- 

 ducting air. There are many uses 

 of non-conducting air. It is on 

 account of this that snow is such 

 an efficient protection to wheat and 

 other vegetation. Ice houses have 

 double walls with the space between 

 filled with sawdust. Many houses 

 now have double windows. Loosely 

 woven cloth is warmer than the ( ^ 



same weight of closely woven ma- 



terial. Loose and fibrous materials are always poor con- 

 ductors on account of the air entrapped between their 

 fibers. 



