84 



Reuben T. Patton : 



The ratios are only calculated for the period of active drying. 

 In the last table it will he seen that the values of the ratios approach 

 the value of the root of the time. In the 40° experiment the ratio is 

 actually t. From all the tables it will be seen that the ratio of the 

 first day's loss to any subsequent loss always lies between " t" and 

 " yi." It never goes outside these limits. With high humidities 

 the curve of loss always approaches a straight line. The nearer, 

 however, that the curve of loss approaches a straight line the slower 



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AVERJCE CRCEN 

 WEIGHT a3-4< ma. 











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Time in days. 



FIG. 9 



Two Types of Drying Curvks, Thk Upper High Temperature and Low Humidity, 

 The Lower Low Temperature and High Humidity. 



the drying, as is well shown in Fig. 9. In this last figure are shown 

 two curves of loss, one for drying at 50°C. and 15 per cent, humidity, 

 the other at 20 °C. and 80 per cent, humidity. In both cases the 

 vapor pressure was 14 mm. Each curve is the average of three 

 results. The slower the drying the nearer the curve approaches the 

 time axis. The general formula for this period of drying is ^=a<& 

 where & varies from unity to '5. As 6 increases in value from -5 to 

 1, the value of " a " decreases. The smaller the value of " & " within 

 the limits stated the faster the rate of drying. Rapid drying, how- 

 ever, although advantageous from the point of view of saving of time 

 increases the amount of shrinkage. This is not surprising, for it is 

 quite conceivable that the higher temperatures make the wood some- 

 what plastic. Increase of shrinkage is very undesirable from a com- 

 mercial point of view. What has recently been termed collapse in 

 timber is in many cases undoubtedly due to high temperatures in the 

 kiln. In Table VIII. are given the amounts of shrinkage for a series 

 of oak blocks, averaging 2 06 cms. in thickness. Three blocks were 



