THE INCUBATOR AND ACCESSORIES. 249 



pands and forces up the mercury, which tends to close up /. The 

 adjusting- screw should be again turned outward, if need be, to pre- 

 vent this from happening-. When the temperature in the incubator 

 has reached the desired point, for example, 37, the adjusting- screw 

 should be turned in till the mercury just closes the opening-/, of the 

 delivery tube. The minimum opening- now supplies the gas to the 

 burner. This minimum supply should now be reduced, as much as 

 possible, by turning- C. without causing- the flame to shoot down inside 

 of the burner. As soon as the temperature drops, the mercury con- 

 tracts, and thus allows g-as to escape from/. In a few minutes the 

 increase of heat causes the mercury to again shut off the main supply 

 of gas. 



Inasmuch as alcohol boils at 78, the alcohol regulator should 

 not be used to maintain a temperature above 70. For temperatures 

 above this point the bulb should be filled entirely with mercury, or 

 the alcohol may be replaced by air or by anilin, which boils at 185. 

 The ordinary adjusting screw cannot be used when a high tempera- 

 ture is to be maintained. For such purposes the regulator should be 

 provided with a glass stop-cock, which connects with a small cup 

 filled with mercury (Fig. 37 D'). When the gas-supply is turned off, 

 as in the case of a water-bath or oven, this stop-cock should be 

 opened. 



The adjustment of the ordinary mercury regulator is similar 

 to that just mentioned. Frequently, the thread of mercury is broken 

 and air is thus introduced into the capillary tube. This can be re- 

 moved by inserting a thin platinum wire, or a drawn out capillary 

 glass-tube, and gently turning it about. Care should always be taken 

 to remove the air that may be present in the arm D. 



Obviously, a continual fluctuation in the temperature 

 of the incubator will exist. A good alcohol regulator, 

 however, should not allow a variation of more than one or 

 two-tenths of a degree. The greater the volume of water 

 in an incubator the more constant will be the temperature. 

 The latter, in that case, will be likewise more independent 

 of any variation in the pressure of the gas. Frequently, 

 the pressure of the gas is so variable that it is not possible 

 to maintain a perfectly constant temperature in an incubator, 

 even when this is provided with the best form of regulator. 

 This difficulty can be obviated by employing a gas-pressure 

 regulator. 



