APPARATUS, MATERIAL, AND REAGENTS. 635 



connected with the entrance and exit gas tubing respectively. The 

 pressure of the incoming gas raises the bell (B) ; and with it the valve 

 (d) is raised towards the opening at c c. The weight (h\ which is 

 replaced on #, by its downward pressure counteracts this upward 

 pressure of the gas and opens the valve (c c). Thus the flame is 

 best regulated in the morning, when the pressure is at a minimum ; 

 then supposing an increase of pressure occurs, the weight of h is 

 overbalanced, B is raised, and with it d, and the gas supply pro- 

 portionately diminished by the gradual closing of the valved opening. 



Reichert's Thermo-regulator. This regulator (Fig. 270) 

 consists of three parts a hollow "["-piece, a stem and a bulb. 

 The T -piece fits like a stopper in the upper widened 

 portion of the stem. One arm of the T is open 

 and connected with the gas supply; the vertical 

 portion terminates in a small orifice, and is also 

 provided with a minute lateral opening. The stem is 

 provided with a lateral arm, and this arm, the stem, 

 and the bulb contain mercury. The regulator is 

 fixed in the roof of the incubator, so that the bulb 

 projects either into the interior of the incubator or 

 into the water-chamber. When the incubator reaches 

 the required temperature, the mercury is forced up 

 by means of the screw in the lateral arm, until it FIG. 270. 

 closes the orifice at the extremity of the vertical R TMO' S 

 portion of the T- The gas which passes through REGULATOR. 

 the lateral orifice is sufficient to maintain the 

 apparatus at the required temperature. If the temperature of the 

 incubator falls, the mercury contracts, and gas passing through the 

 terminal orifice of the T increases the flame of the burner, and 

 the temperature is restored. 



Page's Thermo-regulator resembles the above, but instead 

 of the T~ -piece there are two pieces of glass-tubing. The outer 

 tubing envelops the upper part of the stem of the regulator, and 

 admits of being raised or lowered. The upper end of this tubing 

 is closed by a cork, which is perforated to admit the narrow glass- 

 tubing, which represents the vertical arm of the J, passing within 

 the stem of the regulator. This has a terminal and a lateral 

 opening, and is the means of entrance for the gas. This regulator 

 is adjusted by noting when the thermometer indicates the desired 

 temperature, and then pushing down the outer tube until the 

 terminal opening of the inner tube, which is carried down with 

 it, is obstructed by the mercury. 



