RESULTS 



Equilibrium Moisture Content 



The sorption EMC tests were always started from a moisture content either higher 

 or lower than any EMC expected. The desorption tests started from a high moisture con- 

 tent that ranged from 28.2 to 31.7 percent and averaged 29.6 percent. The adsorption 

 tests started from a low moisture content between 2.6 and 3.4 percent that averaged 3.0 

 percent. The relative humidities used for conditioning and the EMC's that resulted 

 are given in table 1. The differences between adsorption and desorption EMC's are less 

 than 2.0 percent at humidities under 70 percent. Above 70 percent relative humidity, 

 the difference became greater than 2.0 percent, approaching 3.5 percent at 90 percent 

 relative humidity. 



Table 1 . --Adsorption and desorption equilibrium moisture contents of ponderosa pine 

 needles with starting moisture contents of 2. percent for adsorption and 29. 6 per- 

 cent for desorption 









: Average : 



Average 



Hysteresis 





Dryl : 





: adsorption : 



desorption : 



of 



Salt : 



Relative^ 



: moisture : 



moisture : 



moisture 



solution : 



bulb : 



humidity 



: content : 



content : 



content 





°F 





- - - - - Percent 







LiCl 



75 



13 



4.3 ±0.2 



5.9 ±0.2 



1.6 



MgCl2 



75 



33 



7.5 ±0.4 



9.0 ±0.0 



1.5 



Mg(N03)2 



75 



53 



10.2 ±0.2 



11.9 ±0.1 



1.8 



NaCl 



75 



71 



13.2 ±0.0 



15.3 ±0.2 



2.1 



KNO3 



75 



91 



19.2 ±0.1 



22.6 ±0.0 



3.4 



^ Dry bulb temperature was maintained at 75°F ±5° (24° C ±2°). 



^ Relative humidity is the measured value and differs in some cases from values 

 for chemically pure salts. 



Moisture Response Time 



Desorption and adsorption moisture response tests at 80° F (27° C) air temperature 

 were run on individual needles and litter beds of the three bulk densities (fig. 3). The 

 response time of materials to water vapor gradients is also called moisture timelag 

 (Nelson 1969; Mutch and Gastineau 1970; Fosberg and Deeming 1971), and the moisture 

 time constant (Van Wagner 1969) . In each case, the expression is used to describe the 

 exponential sorption process of the following equation (from Nelson 1969): 



m - m 



^ E = Kexp(-t/r) (1) 



o e (Con.) 



5 



