KILN DRYING HANDBOOK. 61 
perature will undoubtedly be higher there than in the upper and 
lower passages. 
PLACING OF SAMPLES. 
The placing of samples is of prime importance, and a large num- 
ber. 10 or 12, should be used for each run until the behavior of the 
kiln is well determined. Samples should be so placed in the piles of 
lumber that they will receive exactly the same drying treatment 
as Vae lumber itself. They should be located on both entering-air 
and leaving-air sides of the piles, high, low, and halfway up, so that 
the relative drying effects can be determined. In case of erratic 
circulation or trouble from uneven drying, samples can also be placed 
in the middle of the piles; on these there will be no intermediate 
weighings possible. In progressive kilns, or any type operating at 
high temperatures, the obtaining of intermediate weights on any of 
the samples is often a difficult matter. When the kiln has been 
loaded steaming can start immediately. A full supply of high- 
pressure steam should be available, so that the steaming temperature 
may be reached quickly and full saturation of the air assured. 
Care must be used to prevent possible injury to the instruments as 
the kiln is heated ; the steaming temperature will probably be higher 
than that for which the regulators are set, and if these are of the 
liquid-filled type the excessive pressure developed may strain the 
bulbs or diaphragms or cause the valve to stick on its seat. 
After the drying conditions have been established a study should 
be made of the circulation. This study can well be supplemented 
by the use of a number of wet and dry bulb hygrometers scattered 
throughout the kiln, preferably near the various samples. The read- 
ings of these will give a good idea of the relative drying conditions 
at these points. The readings should be tabulated and the relative 
humidity determined. The variations in the relative humidity are 
a good indicator of the variations to be expected in the drying rate 
throughout the kiln. In progressive kilns the matter is more diffi- 
cult, and more reliance must be placed upon circulation tests and 
upon the moisture content of the samples in the dry stock. If wet 
and dry bulb hygrometers are used in progressive kilns to determine 
uniformity of drying, they should all be placed on a single truck at 
a time, since variations from end to end are to be expected. 
The samples should be weighed frequently enough so that there 
will be at least 5 determinations for the kiln run; in the case of 
runs extending over more than 10 days, the samples should be 
weighed every day. The moisture per cent should be calculated 
immediately, and a chart should be maintained, showing graphically 
the loss of moisture day by day. On this same chart may be plotted 
the daily temperatures and humidities. This can then be compared 
with the drying schedule and differences noted and corrected. If 
preferred, the temperature and humidity of the schedule may be 
plotted on the same sheet, thus giving a useful comparison between 
the schedule and the actual run. (See Fig. 12.) 
KILN RECORDS. 
In addition to this chart, it is desirable to keep a permanent 
record of the details of each run. Forms for this purpose are 
provided by some of the kiln companies and can well be used wher- 
