228 TOBACCO LEAF. 



whether the air is too humid, hang a psychrometer 

 (Fig. 57) between the plants in a central part of the 

 barn. The wet bulb in this instrument should show a 

 depression below the dry bulb of not less than one and 

 one-half or more than two degrees. If the wet bulb 

 shows a greater depression, it indicates that the air is so 

 nearly saturated with moisture tha,t it can no longer 

 take up the water given off by the leaves. This is the 

 condition that induces pole burn. Now apply artificial 

 heat to dry the air, opening the upper ventilators to 

 carry off the heated moist air, and the danger will be 

 averted. Keep up the heat until the psychrometer gets 

 back to the desired standard wet bulb not less than 

 one or more than two degrees below dry bulb. 



From these Wisconsin experiments, the conclusion 

 seems warrantable, that with a temperature within the 

 curing house of not exceeding 75 F., a degree of atmos- 

 pheric humidity represented by a wet bulb depression of 

 one and one-half degrees, when the psychrometer is be- 

 tween the plants, and is not exposed to unusual air cur- 

 rents, does not endanger the tobacco to pole burn, and 

 that an occasional variation to one degree is safe, at 

 least if not prolonged. But a wet bulb depression of 

 less than one degree is dangerous, and if prolonged, is 

 almost sure to result in pole burn. It will be wise to 

 make one and one-half degrees of depression for the wet 

 bulb the minimum, rather than one degree, not because 

 one degree is dangerous, but because it provides too lit- 

 tle margin between the safety and danger limits. The 

 atmosphere throughout the curing house cannot be 

 changed immediately by starting the fires, and if these 

 are started as soon as the wet bulb depression becomes 

 less than one and one-half degrees, if the weather is 

 becoming rapidly damper, it might sometimes be 

 difficult to prevent the atmosphere within from be- 

 coming so damp as to register less than one degree 



