April, '10] COTTON: LOW TEMPERATURE APPARATUS 145 



The thermo-regulators, which are the vital part of the plant, were 

 made by a local firm. The mechanical principle involved constitutes 

 the most important forward step in temperature control that has been 

 made in the past century. They are simple, extremely sensitive, 

 reliable and almost indestructible if properh^ handled. The re^lator 

 is in the form of a very thin, steam brass bellows about 5 inches in 

 diameter and 314 inches high and is partly filled with an easily vola- 

 tilized liquid after which it is hermetically sealed. 



A rise in the temperature of the air in the chamber causes a por- 

 tion of the liquid to volatilize, exerting an expansive pressure on the 

 bellows, which is so housed tli^t it can expand in one direction only. 

 To the free end of the bellows is fastened a pin which extends through 

 the wall of the chamber, and engages the lower end of a rocker arm 

 to the upper end of which is attached the stem of the balanced valve. 



The balanced valve remains closed so long as the air in the chamber 

 is at or below the temperature for which the bellows is adjusted. 

 "When the temperature rises above this point the bellows expands, 

 exerting a thrust against the lower end of the rocker arm, opening 

 the valve and allowing the cold brine to flow through the coils until 

 the temperature again falls to the predetermined point. Adjustment 

 is secured by means of a 5-pound sliding weight carried on a rod 12 

 inches long, projecting at right angles to the rocker arm (Fig. 27). 



In actual practice the valve is probably never opened wide. The 

 rising temperature begins to act on the liquid in the bellows before 

 the temperature for which the latter has been adjusted is reached. 

 This opens the valve the merest trifle, allowing a very thin stream 

 of the colder brine to pass through and mix with the body of brine 

 already in the coils, reducing its temperature and closing the valve 

 before enough brine has passed through to entirely replace that 

 present when the valve began to open. A pressure of 10 to 15 pounds 

 on the brine system admits of a more sensitive control than a higher 

 one because with the higher pressure the whole body of brine in the 

 •coils is pretty sure to be replaced by brine several degrees colder 

 before sufficient cold radiates from the coils to close the valve, con- 

 sequently the temperature of the air in the chamber will be carried 

 several degrees below the desired point before the balance is again 

 ■established between the brine and the air. 



Mr. Conradi: I would like to ask the cost of this low temperature 

 apparatus, as described. 



Mr. Cotton : About fifteen hundred dollars. 

 3 



