May 12, 1923 
Rhizopus Responsible for Sweet Potato Decay 
443 
means of a funnel into a pan located in the door of the chamber. A 
mercury thermoregulator, which is connected to the heating coils and a 
250-ohm relay on a nearby switchboard, is suspended by a rubber band 
on the back wall. The air within the chamber is kept in motion by means 
of an 8-inch fan run by a motor located just outside the chamber. The 
thermoregulator is similar to that designed by Clark (/), but differs 
from it in that there are three arms of mercury instead of one and that 
one of the electric connections is made directly to one of these arms instead 
of through a special tube. 
The storage house was constructed according to Government plans 
(7). It is provided with two stoves, one at each end, to furnish heat 
during the curing period, and with steam radiators, one flanking each 
corner, for the control of the temperature during the winter. 
CONTROI. OF ATMOSPHERIC ENVIRONMENT IN THE INFECTION 
CHAMBERS 
TEMPERATURE 
The thermoregulator used in the chambers controls the temperature 
within one-half of one degree. The fineness of the control will depend 
upon the size of the mercury column in the capillary tubing, the amount 
of mercury used, and its surface area. 
The amount of current that passes through the heaters materially 
affects the control of temperature. Two amperes with a voltage of no 
is all that a 250-ohm relay will handle; in fact, sticking of the relay may 
be expected at times with this amount. If more current is desired a 
larger relay should be employed. An ampere and a half is the most that 
is used in any of the chambers. 
To further reduce the danger of sticking, a condenser of iX micro¬ 
farad capacity is employed in connection with each relay. With 
this type of equipment 20 chambers have been run for 9 months 
without a single case of sticking. 
The capacity of the heaters should be limited to the amount of heat 
required to heat the chamber to within a few degrees above the desired 
temperature, otherwise there is a tendency for the temperature to 
fluctuate or lag. 
The amount of current that flows through the thermoregulator should 
be reduced to a minimum consistent with efficient operation, otherwise 
the mercury and contact points become insulated and prevent efficient 
operation. 
Direct current is preferable, particularly where mercury thermoregu¬ 
lators are employed. Current with a low number of cycles should not 
be used when avoidable, since the vibration set up by such a current 
does not contribute to effective control. 
The contact points on the relays should be kept tight, in position, and 
clean; otherwise they become insulated by the finely divided metal 
thrown off, especially where a considerable amount of current is used, 
and thereby reduce the current below that actually required to main¬ 
tain the desired temperature. 
A uniform temperature throughout each chamber was obtained by 
the use of an 8-inch fan running at about 700 revolutions per minute. 
The temperature of the air surrounding a chamber was below that of 
the chamber, and the desired temperature obtained by heating. The 
lower temperatures were obtained by placing the chambers in cold stor¬ 
age rooms where the temperature had been reduced by refrigeration. 
