DEW 139 



total amount which the air does hold is called absolute hu- 

 midity. The absolute humidity divided by the saturated 

 humidity is called relative humidity. It is the latter which 

 concerns us. The higher the temperature, the more water can 

 exist as vapor; therefore warming a house seems to dry it, 

 although the same amount of water may be present as when 

 it was cold. The relative humidity should be between 70 

 per cent and 75 per cent. A further consideration of hu- 

 midity will be studied in Section 190, Dangers of Vitiated Air, 

 in connection with ventilation. 



References : 



1. 1103:122. Atmospheric Humidity. 



2. 1304:244-245. Humidity. 



3. 1803 : 100. Humidity of the Atmosphere. 

 a. 1102:144-146. Humidity. 



6. 1302:281-282. Humidity. 



c. 1303:60-61. Humidity. 



d. 1305:66-68. Humidity. 



e. 1308 : 93. Humidity and its Condensation. 

 /. 1309:239. Humidity. 



g. 1310:364-366. Humidity. 

 h. 1311:226-227. Humidity. 

 i. 1312 : 379-380. Absolute and Relative Humidity. 



EXPERIMENT FOR THE TEACHER 

 Moisture in the Air 



Expose a thin layer of sulphuric acid (concentrated) in a 

 large open glass dish. Weigh before and after exposure of 

 twenty-four hours. 



102. DEW 



There is an old saying that dew falls, but this is not the 

 truth, since the dew is formed at the place where it appears. 



