6 BULLETIN NO. 161 



of the ground in the orchard area. When heat starts through 

 a gas, part of the heat is absorbed and part of it goes through 

 unobstructed. The gases that are the best heat absorbers and 

 therefore the ones that would prevent the escape of the heat of 

 the ground best are water vapor, carbon dioxide, ammonia, 

 gaseous hydrocarbons, dust, and smoke. These would be the 

 best mantles, (c-d). 



CARBON DIOXIDE AS A SMUDGE WITHOUT THE 

 ADDITION OF HEAT 



During the spring of 1910, under the direction of Prof. W. 

 H- Homer, Jr., who was then Horticulturist at the Utah Experi- 

 ment Station, ninety-six pounds of carbon dioxide were liberated 

 in one acre of an orchard during a period of two and one-half 

 hours in the night by drawing a tank of the gas, with the valve 

 opened, back and forth through the area mentioned. This gas 

 not only failed to keep the treated area warmer than the adjoin- 

 ing section, but actually cooled it slightly. This may be due to 

 the fact that the gas as it leaves the tank expands rapidly be- 

 cause of the fall in pressure and therefore cools to a temperature 

 of about 32 F. Difficulty was experienced in liberating the gas 

 because the valve kept freezing up. (This subject will be con- 

 .sidered further, at a later point in the bulletin.) 



SPRAYING OF WATER 



Inasmuch as water is a good heat absorber, it was thought 

 that to spray water into the air above the trees might be ef- 

 fective in preventing injury by frost- In the spring and fall of 

 1912, we so treated an acre of apricots in the orchard of W. H. 

 Homer, Jr., at Pleasant Grove, Utah, at his suggestion. It indi- 

 cated probable success from the fact that the source of water sup- 

 ply had a temperature of 55 F. and, having at hand a large 

 amount of it, it was expected that considerable heat would be 

 given out to the orchard when this water cooled to 32o F., the heat 

 capacity of the water being so large, and that again on arriving 

 at 32o much heat would be again evolved as the water froze. 

 When the sun fell on the orchard in the morning, we had hopes 

 that the air would not warm up so fast as the air in the adjoining 

 orchard, and that because of the slow rate of thaw the damage 

 would probably be less. This water was piped to the top of each 

 of the trees and was forced out under 50 pounds pressure in a 



(c). Preston Theory of Heat, p. 556. 



(d). Weather Bureau Bulletin C, D, and G, p. 125. 



