JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. Ill, FEBRUARY 4, 1913 No. 3 



PHYSICS. — Suggestions for frost protection. Kakl F. Keller- 

 man, Bureau of Plant Industry. 



The high thermal capacity of water has made possible the 

 development of more or less elaborate enclosed systems for warm- 

 ing air spaces, such as living rooms, but very little attention has 

 been paid to the utilization of water in efforts to protect orchards 

 from frost. It would seem, however, that the rapid and efficient 

 distribution of heat occasionally necessary in orchards, where 

 modern systems of frost prevention are employed, could be con- 

 trolled more satisfactorily and with less expense thru a develop- 

 ment of water-heating systems. 



The rapid evaporation when fine sprays of water are driven 

 into the open air in summer weather has a cooling effect, due to 

 the absorption from the air of a quantity of heat equal to the 

 latent heat of vaporization of the water evaporated, which is so 

 far in excess of the quantity of heat delivered to the system by 

 the water introduced, that a short experiment under these con- 

 ditions is misleading. The rapid decrease, with decreasing tem- 

 perature, of the tension of aqueous vapor would make easily 

 possible the artificial saturation of air at or below 0°. As soon 

 as this artificial dew-point has been established the high calorific 

 value of water vapor, or finely divided particles of water, would 

 become operative. 



Three methods of thus utilizing water appear possible: (1) the 

 atomizing, or spraying by the use of power sprays, of fine mists 



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