Oct. 27, 1923 
Automatic Control of Low Temperature 
185 
and discharging it into the two other rooms, the quantity of cold air 
required to maintain the desired temperature being regulated by dampers 
in the discharge pipe from the fan. The dampers are manipulated by 
means of solenoids connected by bell cranks to the dampers, the sole¬ 
noids being energized by electric currents controlled by thermostats 
located in these rooms. 
In the culture room it has been found practicable to maintain a tem¬ 
perature for long periods with a variation in the liquid of not more than 
±o.i° C. from the desired temperature. The variation in the room, 
however, is somewhat greater, but not more than i° C. 
In the instrument room the temperature variation is slightly greater 
than in the culture room, owing to the opening of doors and to the presence 
of the person reading the instruments. A slight variation in temperature 
Fig. i.—A rrangement and construction of compartments used with low-temperature-control system in 
plant physiology. 
in this room, however, is of little importance, for the reason that the 
specimens are immersed in a solution and the short time in which they 
are kept in the instrument room has but little effect on the temperature 
of the liquid. 
The original refrigerating plant consisted of two complete %-ton 
ammonia refrigerating outfits, one being held in reserve in case of a 
breakdown of the other. Direct expansion of the ammonia in the coils 
located in the coil room was employed. These machines were used 
because they were already on hand, but although great precautions were 
taken to prevent leaks, ammonia would escape from time to time and 
destroy or injure the plants and interfere with the work; subsequently 
a hermetically sealed sulphur dioxid outfit was installed and calcium 
chlorid brine was employed as the cooling medium, thus eliminating the 
danger of escaping ammonia. The temperature of the brine in an insu- 
