KILN DRYING HANDBOOK 5 
bearings improve its sensitivity, which with ordinary metal bearings 
is 0.05 gram and with agate is about 0.02 gram. An agate-bearing 
triple-beam balance of good quality (pl. 1, B) is reasonably satisfac- 
tory also for small pieces, such as moisture distribution sections. 
(See below.) Balances can be obtained from most dry-kiln manu- 
facturers and from dealers in scientific instruments. 
Several forms of calculating scales, developed particularly for 
moisture-determination work, have merit; some types permit direct 
reading of the moisture content, without calculation. 
The large scale required for kiln samples is described on page 88, 
and pages, 94 and 95 present a list of necessary equipment, 
DRYING OVENS 
Several kinds of ovens for the drying out of moisture sections are 
on the market. Most of them are electrically heated and practically 
all of these in addition are provided with thermostatic control, which 
keeps the temperature accurately at the desired point. (Pl. 2, A.) 
Steam-heated ovens, which are convenient and are free from trouble, 
will be found excellent where a suitable supply of steam is continu- 
ously available. Ovens of this kind are commonly homemade. ‘The 
walls and the doors can be of galvanized iron, built hollow with a 
1%-inch space filled with mineral wool, and the heating element can 
be conveniently made of 1-inch or 114-inch pipe; both the insulation 
and the heating surface must be adequate for the heating capacity of 
'the steam supply. Ventilators should be fitted to the top, and pro- 
vision should be made under the steam pipes for the entrance of fresh 
air. ‘The temperature is usually regulated by means of a reducing 
valve on the steam line and dampers on the ventilators. For each 
cubic foot of volume above the heating coils in the oven there should 
be at least 1% square feet of heating surface and 6 square inches of 
ventilator area. Shelves should be provided for the moisture sections. 
Various kinds of hot plates are available in place of ovens to dry 
out moisture sections. It is customary to use very thin sections with 
these hot plates and to leave them on only a short time—15 to 45 
minutes. Such a hot plate is cheaper than a regular oven, and in 
the hands of a skillful operator can be made to yield good results, 
but it can not be recommended except as a makeshift. 
DISTRIBUTION OF MOISTURE IN STOCK DURING DRYING 
It is very helpful, except in the simplest kinds of drying, to know 
how the moisture is distributed through the cross section of the 
board or other piece of stock, and to secure this information moisture 
distributions are made. In so doing a moisture section is obtained 
in the usual manner, but instead of being weighed as a whole, it is 
cut or spht so as to separate the core from the outer portion, called 
the shell, and distinct moisture determinations are made on each 
part. The shell will usually be in two or four pieces, which can be 
weighed most conveniently as a single unit. For thick stock it may 
be desirable to divide the sections into three units, a shell, an inter- 
mediate part, and a core. The further procedure is then precisely 
the same as before, the pieces of the intermediate part being weighed 
