3i8 Journal of Agricultural Research voi. v. no.s 



bottle filled with pieces of pumice as large as will pass through the narrow 

 neck. In this reservoir the water is mixed so that any change in the tem- 

 perature of that entering the bottle, due, for instance, to fluctuations in 

 the voltage of the current in the preheater, will be dissipated through 

 the mass to such extent that there will be no rapid fluctuations in the 

 temperature of the water leaving the bottle. From this reservoir the 

 water enters the final heater which completes the heating necessary to 

 bring the water to the desired temperature. This device functions 

 automatically and varies the amount of heating it does to accord with 

 the fluctuations in temperature of the water coming from the mixing 

 bottle. From the final heater the water flows into a smaller mixing 

 bottle, from which it passes to the heat absorber. 



WATER COOLER 



To cool it, the water from the pressure tank is passed through a coil 

 of pipe submerged in cold water, in a tank nearly i meter in length by 30 

 cm. in width and depth and containing 80 to 90 liters of water. The 

 coil consists of nearly 6 meters of iron pipe, of 15 mm. bore, in six parallel 

 rows running from end to end near the bottom of the tank. The water 

 in the tank is chilled by cold brine flowing through a second coil, immersed 

 in the water above the former coil. A small ethyl-chlorid refrigerating 

 machine keeps the temperature of the circulating brine quite uniform. 

 In this manner the temperature of the water leaving the cooling coil is 

 readily kept below that at which it may be needed at any time during an 

 experiment, and fairly uniform, but it can not be regulated by cooling 

 alone as closely as needed for use in the heat absorber. 



WATER HEATER ADJUSTED BY HAND 



The preheater consists of several coils of electric-resistance wire of 

 different sizes wound upon a thin- walled brass tube about 16 mm. in 

 diameter, from which they are insulated \\dth mica. Outside of this is a 

 similar tube about 26 mm. in diameter, and the annular space between 

 the two and surrounding the resistance coils is filled with sand, so that 

 the heat generated by the electric current in the resistance wire is trans- 

 mitted rapidly to both tubes. This heater is mounted inside a brass 

 tube 37 mm. in diameter, in such manner that the chilled water, entering 

 the large brass tube, flows in one direction along the outside of the heater 

 and returns along the inside, absorbing all the heat generated in it. By 

 means of plug switches on the base supporting the heater various combi- 

 nations of the coils may be put into service, as desired, to vary the 

 heating. By the use of this device the temperature of water flowing at a 

 rate of about i liter a minute may be increased nearly 10 degrees, if 

 desired, in increments of about 0.25 of a degree. 



