TEMPERATURE REGULATORS 



61 



FIG. 48. Roux's metal regulator. 



The left limb of the U is fixed while the right limb R is free, and therefore 



any change of shape resulting from a rise or fall of temperature in the incu- 

 bator is integrated on the free limb R, and transmitted by means of a rigid 



horizontal bar T to a piston placed 



outside the incubator which controls 



the supply of gas. 



The tube C being connected to a 



gas tap, the gas must pass under E to 



reach the chamber to which the tube 



D leading to the burner is connected. 

 As the temperature in the incubator 



rises, the free limb R is drawn towards 



the other limb taking the rigid bar T 



with it ; the piston, controlled by a 



spring, closes (this is shown in 'the 



figure), only leaving a small safety hole 



or by-pass V by which the gas can 



pass to the burners, and accordingly 



the temperature is lowered. When 



the temperature is too low, the changes 



described are reversed ; the bar is pressed upon by the right limb of the U, 



and this in turn forces the piston E out so that more gas passes to the burners 



and the flames are larger. After a few oscillations, the temperature in 



the incubator will become constant. 



By altering the length of the rigid bar T by means of a screw, the 



temperature can be raised or lowered as required ; or as in the pattern 



shown in the figure, which gives more delicate control, the length of the 



rigid bar is fixed while the length of the piston can be altered by means of 



screws. 



In some cases the zinc and iron bars are straight, and the apparatus assumes 



the form of a metal tube. This modification is useful when the regulator 



has to be immersed in water, as for instance 

 in a water bath or a water- jacketed in- 

 cubator. 



Roux's regulator can be utilized for con- 

 trolling the temperature of gas stoves used 

 for heating incubating rooms and stoves in 

 laboratories. 



SECTION II. INCUBATORS HEATED BY 

 COAL GAS. 



A. Hearson's incubators (fig. 49). [These 

 are most satisfactory incubators, and are 

 almost if not quite the only ones used in this 

 country. There are two forms, a " hot in- 

 cubator " for temperatures of about 37 C. 

 and a " cool incubator " for 20 C. or there- 

 abouts. Incubators on the same principle 

 FIG. 49. Hearson's" warm ''incubator can however be obtained to work at any 



arranged to work with gas. , 



temperature above 16 C. 



[1. The "warm" incubator. This, when once set, will work perfectly for 

 months together without adjustment of any part and without any attention 

 beyond the occasional addition of a little water to replace the small amount 



