i8 
Journal of Agricultural Research 
Vol. XXV, No. I 
through a cylindrical connection to the culture chamber. In this passage 
its temperature was raised by electric heaters which were controlled by 
a thermostat placed within the latter chamber. By this treatment the 
relative humidity of the air was reduced toward the desired value. 
HUMIDIFIERS 
The humidifiers were constructed from heavy galvanized iron sheeting 
after the plan of one described by Shamel (34). At the higher tempera¬ 
ture 50 per cent greater length and capacity were provided than at the 
lower one. Each consisted of an upper tray 37.5 cm. wide and 5.6 cm. 
deep, resting upon a chamber 30 cm. in both width and depth. The tray 
consisted of troughlike sections 5 cm. in width and depth, so soldered 
together as to provide slits through which could be passed strips of 
toweling 30 cm. wide and 45 cm. long. The latter which were of coarse, 
open-meshed linen, were secured near one end to the bottom of the 
humidifying chamber by means of iron rods passed through loops in the 
toweling. The other end was drawn firmly through the slit above and 
fastened with brass clips. In this way one end of the toweling was 
bathed by water as it flowed through the tray and the other end was 
immersed in the overflow as it returned over the bottom of the chamber 
below. Baffle plates were arranged to direct the water and air currents 
completely in contact with the toweling. The water was heated by 
luminous radiator units of either 250 or 500 watts capacity. These 
were placed in copper cylinders which were sealed concentrically within 
iron ones, the water flowing between the two. A mercury thermo¬ 
regulator which controlled these heaters was immersed in the water 
current near the entrance to the tray. Passing to the chamber below 
by a drainage tube, the water escaped to the drain through a siphon, 
thus preventing interference with its removal by the air current. The 
latter was provided by a No. 00 Buffalo forge blower operated continu¬ 
ously by a small electric motor. Air entered the humidifier at one end 
through a circular orifice 9 cm.*in diameter and escaped to a heating 
cylinder through a similar orifice near the other end of the chamber. 
Here it was further heated by eight small cylindrical units of a capacity 
of 28 watts each, operated by a bimetallic thermostat suspended on the 
wall of the culture chamber. In all cases the thermostats were operated 
on 110 volts alternating current through pony relay instruments protected 
by ample resistance. 
Heat insulation of the humidifier was provided by a blanket formed by 
supporting thin asbestos sheeting in cheesecloth. With 12 towels in the 
installation for lower temperature, air which was passed through the hu¬ 
midifier from the surrounding greenhouse at a probable rate of air replace¬ 
ment in the culture chamber of at least once in 5 minutes acquired a 
relative humidity of practically 100 per cent at 12 0 C. In the other in¬ 
stallation, equipped with 18 towels, the relative humidity was adjusted 
to about 90 per cent at 18 0 C. The temperature of the lake water em¬ 
ployed was about 6° in midwinter. 
It was necessary to supplement the heaters of the humidifier at the 
higher temperature. This was done by coiling upon the water feed-pipe 
a section of resistance wire which gave approximately 500 watts con¬ 
tinuous service outside the insulation. Through the further action of 
the heaters in the conduits connecting humidifiers with culture chambers, 
the conditioned air was delivered into the latter at about 17 0 C. and 70 
per cent relative humidity in one case, and 22 0 and 78 per cent relative 
humidity in the other. Thus there was approximated an atmospheric 
