A Consideration of Adverse Temperatures 331 



blossoms with water is practiced, also, with the same purpose 

 in view. . . ." 



Heating the air. 



"The most practical, efficient, and economical method 

 yet devised for protection of large areas is the direct addi- 

 tion of heat by means of numerous small fires properly dis- 

 tributed over the area to be protected." 



The last method, "heating the air," is the only one that 

 calls for further amplification in this connection, since it is 

 the one used in recent years, largely, to the exclusion of the 

 others. The details of practice are essentially the same for 

 all orchards, whether peach, apple, citrus, or some other kind, 

 though the critical temperatures for the various fruits in 

 different stages of development obviously vary somewhat. 



Three kinds of fuel have been used in orchard heating, 

 wood, coal, and oil. Many different grades of oil have been 

 utilized, but usually a rather heavy petroleum product of 

 which several different brands are available have given the 

 best results. An oil having a paraffin base is preferable to 

 one with an asphaltum base, as the residue which remains 

 from burning the latter is objectionable. While various 

 grades of oil, varying in density from about 20° to 30° or even 

 32° Baume, have been used successfully, the lighter oils that 

 have a density of about 29° or 30° are perhaps preferable, 

 though some of the "smudge oils" or "orchard heating oils," 

 as they are variously termed, as heavy as 19° Baume, have 

 given good results. If too heavy, however, they do not burn 

 well ; and if too light, they burn too fast for the best results. 



A half-dozen or more different types of "smudge pots" or 

 heaters are on the market. The maker of each type natu- 

 rally claims for his own points of superiority not possessed by 



