Frost and the Prevention of Damage by It. 19 



Fuel oil of from 25 to 28 gravity is the most satisfactory for use 

 in cither the lard-pail or improved type of heater. This oil leaves 

 very little residue and burns practically as long as heavier oils. 



Types of Oil Heaters. Up to the present time few deciduous 

 fruit crops have been valuable enough to warrant the use of any but 

 the simplest and cheapest types of heaters for protection against 

 frost. Since good results can be obtained with these heaters (the 

 lard-pail type) when a sufficient number to the acre is used, the only 

 incentive to change to a more complicated type of heater is the 

 abatement of the smoke and soot. The indications are that the 

 smudge does not injure deciduous blossoms or fruit to any measur- 

 able degree and its elimination is desirable only on account of the 

 resulting dirt. 



The small open lard-pail heaters are not well suited for the pro- 

 tection of citrus fruits because (1) at the time protection is necessary 

 the fruit is almost ready to be picked and even a small deposit of 

 soot is likely to impair its marketing qualities, and (2) protection is 

 necessary in midwinter, when the temperature is likely to remain 

 below the danger point continuously for 10 or 12 hours and heaters 

 of large capacity and long burning time are required. 



A 5-quart lard-pail heater will burn about 2J hours, but as the 

 oil gets low the amount of heat given off is greatly decreased. The 

 2-gallon lard-pail heater will burn about 4 hours, but little heat is 

 given off after 3^ hours. 



The length of time the larger heaters will burn depends altogether 

 on the amount the drafts are open. To combat the long cold periods, 

 that sometimes visit the citrus districts, without refilling during the 

 night, heaters of a capacity of about 7 gallons should be used. These 

 will burn from 8 to 10 hours at near their full rate. 



More than a score of more complicated heaters have been developed 

 with the idea of improving combustion and reducing the amount of 

 smoke. These run all the Avay from the 3 or 4-gallon capacity short- 

 stack heater (fig. 6) to the high-stack heater of from 7 to 20 gallons 

 capacity (fig. 7). The stacks on the smaller heaters are from 4 to 

 10 inches high, while on the larger heaters they are from 3 to 5 feet 

 high. With one or two exceptions the "down draft" principle is 

 used in all the improved types. Air is admitted through the top of 

 the oil reservoir, causing the oil to burn there and raise the tempera- 

 ture sufficiently to change some of the oil to gas. The gas then passes 

 upward and is burned as it rises through the stack. A supply of air 

 to support combustion is admitted through holes cut in the base of 

 the stack. 



In order to burn clean and supply the desired amount of heat 

 the gas must be given some time to burn before its temperature is 

 ir,0830 20 Bull. 1096 I 



