60 



INCUBATORS 



Entering the smaller tube A (fig. 46), the gas passes by way of its lower 

 obliquely cut end through B to the burner. The outer tube is divided 

 towards its lower part by means of a funnel-shaped glass partition E into an 

 upper and lower part. The lower part R is filled below with mercury, and 

 above with ether vapour. When the surrounding temperature rises the 

 pressure of ether vapour increases, and the mercury rises in the funnel and 

 gradually more or less occludes the lower opening of A, thus cutting off the 

 supply of gas to the burner. A pilot opening is provided, so that the gas 

 shall not be completely extinguished. The apparatus is regulated by raising 

 or lowering the tube A. The regulator is sensitive but fragile. 



FIG. 46. -Ether regulator. 



FIG. 47. Air regulator. 



D. Air regulators. Of these, Bohr's may be taken as an example (fig. 47). 

 In principle they are similar to the ether regulators, air replacing the ether 

 in the latter. 



The regulator is fitted to the incubator with the tap R open, and the 

 reservoir A full of air. When the temperature of the incubator has reached 

 the temperature required, the tap R is closed. If now the temperature of 

 the incubator be raised the air expands, presses on the mercury contained 

 in the U -tube B and forces it upwards thus partially or completely occluding 

 the oblique opening C of the gas supply tube, and so cutting off more or less 

 completely the gas passing to the burner through D. The gas delivery tube 

 is provided with a safety opening as usual. The regulator is sensitive, 

 but being affected by alterations in the atmospheric pressure requires a 

 certain amount of supervision. 



E. Roux's metal regulator. This regulator is composed entirely of metal 

 (fig. 48). It consists of a strip of zinc and a strip of steel soldered together, 

 and then bent in the form of an U. The metal with the greater co-efficient 

 of expansion, zinc, being on the outside, it follows that any increase of tem- 

 perature will cause the open ends of the U to approach each other ; and 

 conversely if the temperature of the metals be lowered the gap between the 

 limbs is widened. 



