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48 BULLETIN 1136, U. S. DEPARTMENT OF AGRICULTURE 
the starting point of the schedule, and the humidity should be as 
near 100 per cent (the saturation point) as possible. 
In general, the schedules are apphcable to the further drying of 
stock of any degree of seasoning. Once the preliminary steaming, 
if any, has been given, the drying may be started at the temperature 
and the humidity corresponding to the moisture content of the stock 
as it entered the kiln. The whole of the schedule selected will, as a 
rule, be used only when drying green stock. 'To illustrate: Suppose 
a charge of stock at 25 per cent moisture content is to be dried under 
Schedue 1. The drying conditions proper to start with then are 
those opposite the 25 per cent on the schedule, namely, a temperature 
of 155° I. and a humidity of 60 per cent. As soon as the stock has 
dried 5 per cent, the kiln temperature is to be raised to 160° F. and 
the humidity is to be dropped to 50 per cent, and so on until the 
stock is dry. 
Stock that has been air dried usually has a more moderate mois- 
ture gradient than stock that has reached the same average moisture 
content in kiln drying and for this reason, if the stock is in good 
condition, a schedule somewhat more severe than the one specified 
can be used for it. ‘To do this successfully, however, requires both 
skill and care. , | 
Each schedule is based on dry-bulb temperatures and relative hu- 
midities. The wet-bulb temperatures are the nearest whole numbers, 
taken from Table 1, that correspond to the kiln temperatures and 
humidities desired. , 
The names of woods appearing in the following tables are the 
standard common names given in the Check List of the Forest Trees 
of the United States, Miscellaneous Circular 92 of the United States 
Department of Agriculture. 
GENERAL HARDWOOD SCHEDULES 
The hardwood schedules in Table 2 are intended for use on lum- 
ber of all thicknesses up to about six quarter inches.. Thicker 
stock can be dried by using a schedule one number higher (milder) 
for each additional inch in thickness. 'The schedules have been made 
up for the drying of only one species and one thickness at a time, 
and for heartwood. In drying hardwood it is unnecessary, as a rule, 
to segregate the stock by grade or by character of sawing (quartered 
or plain), and in most cases no attention need be paid to sapwood, 
except to be sure that none is present in the kiln samples. Sapwood 
is much easier to dry than heartwood in practically all hardwoods 
and will dry much faster with a given schedule. In some species, 
such as red gum, it is sometimes possible to segregate the sap boards 
and to dry them separately. When this can be done a relatively 
large saving in time can be effected, especially with green stock 
(p. 60). 
