34 BULLETIN 1375, U. S. DEPARTMENT OF AGRICULTURE 
ELECTRICAL TERMS 
Attention is called to some facts that should be generally known 
about electricity before an electrically heated moisture tester is in- 
stalled. To illustrate some of the factors involved, consider elec- 
tricity as water. The size of the stream of water flowing through 
a pipe woidd be indicated in " amperes " for electricity. The pres- 
sure of the water, or the speed with which it flows, is measured in 
" volts " for electricity. The quantity of water passing through, or 
the gallons of water flowing, is measured in " watts " for electricity. 
The term " kilowatts " merely means 1,000 watts by the regular 
metric system. The term " kilowatt hour," means a kilowatt quan- 
tity of electric current used for an hour's time to light or blow 
breezes or fry an eg:g or sweep the floor or run a moisture machine, 
or to do anything else. 
The large quantity of current consumed by relatively small elec- 
trical heating units is generally not appreciated by the ordinary 
layman not versed in electricity. Take for example, one 6-eompart- 
ment moisture testing machine heated by electricity. Each compart- 
ment requires 5.4 amperes of current at 110 volts pressure or 594 
watts, making 3,564 watts for the whole machine. This amount of 
energy is sufficient to light 125 ordinary 25-watt electric lamps. It 
would generate mechanical power at the rate of almost 5 horse- 
power. 
TYPES OF HEATERS NOW IN USE 
The electric heaters in use in 1925 are of two general types. One 
of these general types consists of a sheet-metal box 5 by 5 inches 
square, iy 2 inches deep, the upper side of which is open except for 
a heavy wire netting which allows the developed heat to rise into 
the compartment of the tester. The heating elements or resistance 
coils of this type of heater stretch between two porcelain barriers 
within the box. The heaters are fastened to the outer edge of the 
tester compartment with hinges and are held in place under the com- 
partment by a spring metal clip at the rear. On the floor of the 
heater is a thin sheet of asbestos which prevents the resistance coils 
from touching the metal boxes and which functions at the same time 
as a means of keeping some heat from being lost to the outside. As 
a rule, these heaters are wired to take a voltage or pressure of 110 
or 220 volts and the resistance wire within the heater is made of 
such diameter and length as to take a current of 4.6 amperes for 
the 110- volt current or 2.3 amperes for the 220- volt circuit. Ex- 
pressed differently, they are so wired that they will develop 500 
watte of heat energy per heater. It will be shown later, however, 
that 500 watts will not develop sufficient heat to give a standard heat- 
ing time of 20 minutes. 
Experiments have demonstrated that because of the excessive heat 
leakage from this type of heater, caused by lack of insulating mate- 
rial at the base and sides of the neater, not more than 25 per cent of 
the possible heat energy developed by the heater is transmitted to 
the compartment of the tester when this heater is in operation. 
Furthermore, since this type of heater has very little heat-retaining 
capacity, it has to be used on a constant and uniform electric circuit 
