FROST 141 



Experiment 54. Dew Point. 



Apparatus: Small, brightly polished, nickel-plated, cy- 

 lindrical brass dish 1" X 3" (a shaving-stick box is excellent, 

 for this purpose), rubber stopper with three holes, to fit, ther- 

 mometer, all glass, right-angle glass tube, syringe bulb, 

 rubber tubing, ring stand. 



Materials: Ether. 



a. Fill brass tube one third full of ether, push the ther- 

 mometer into one hole, the right-angle tube into a second hole, 

 of the stopper, and insert it in the top of the brass tube. At- 

 tach the syringe bulb, by means of rubber tubing, to the right- 

 angle tube. Support the brass tube by its stopper. 



b. By means of the bulb cause air to pass through the 

 ether, taking care not to breathe on the tube. The tempera- 

 ture falls rapidly, and soon moisture will begin to collect on the 

 outside of the brass tube. Stop forcing air in, and read the 

 thermometer. Wait until the moisture disappears, and read 

 the thermometer again. The average of the two readings is 

 the dew point. 



c. Repeat this experiment early some morning. 

 Knowing the dew point and the temperature, the relative 



humidity may be discovered by means of tables. See ref- 

 erences. 



103. FROST 



Frost is formed in much the same way as dew, although in 

 this case the formation takes place below the freezing point 

 of water, which is 32 Fahrenheit. The invisible water vapor 

 passes directly from the gaseous state to the solid state, with- 

 out any intermediate stage. If the wind is blowing on a cold 

 night, there will be very little frost, and perhaps none at all, 

 because as fast as the air is cooled more air comes in; thus the 



