THE BKOWN-DUVEL MOISTURE TESTER 35 
where the specified voltage and amperage is always at the maximum 
point. As the heat energy developed is proportionate to the voltage 
supplied, a lag or drop in the voltage for a few minutes will be 
readily noticed when this type of heater is used, inasmuch as there 
is no provision for retaining any heat for an emergency period, as 
would be the case if the inside of the heaters were well insulated with 
asbestos or fire clay. 
Another heater of this general style, but of slightly different de- 
sign, is used to some extent. This is identical in all respects with 
the one just described, with the exception that both the top and 
bottom of the box are absent and the coils are suspended between 
mica supports within the walls of the box. Necessarily less of the 
possible heat generated is transmitted to the compartments of the 
tester by this type of heater than with the one described before. 
These heaters are being gradually eliminated from service, and for 
moisture-testing purposes should be eliminated entirely. 
The second type of heater in general use consists of a reinforced fire- 
clay block 4!/2 by 4^2 by 1 inch deep with recessed portions on the 
upper side for installing the heating coils. These heaters are wired 
for 110 or 220-volt circuits, but the resistance coils are of such a size 
that they take only 3.2 amperes of current, and therefore are possible 
of developing only 350 watts of energy. Because of their fire-clay 
structure, much more of the heat energy is transmitted to the com- 
partments of the tester from this heater than from the other type. 
The heater swings on an improvised hinge attached to the inside of 
the back of the compartment and is raised and lowered by means of 
a cam attached to a rod. 
ELECTRICAL ENERGY FOR STANDARD HEATER 
From a theoretical standpoint, enough heat will be supplied from 
a heater properly constructed and delivering 300 watts of energy 
to operate a moisture tester properly, providing none of the heat is 
lost during the interval of the test. But, as a practical matter, the 
electric heaters commonly used to-day in moisture testers must be 
wired to deliver approximately twice this amount of heat energy, or 
600 watt.s, on account of the excessive heat leakage which they 
permit. 
WIRING FOR ELECTRICALLY-HEATED MOISTURE MACHINES 
Observations have shown that although these heaters are wired to 
take either a 110 or 220-volt circuit, it is not always that the specified 
voltage is delivered in every installation to the switch board of the 
moisture tester. Observations have shown that the voltage supplied 
is usually below 110 or 220, apparently for two reasons. 
In the first place, the necessary voltage is not delivered to the 
moisture-testing laboratory by the electric service companies. This 
is notably true at certain large terminal or export elevators which are 
located from 1 to 10 miles from the generating plant. Moreover, 
many isolated plants furnish their own electrical energy, and the 
required 110 volts are not always available. As a general rule, large 
city service is rather regular, although there are notable exceptions. 
