THE INCUBATOR AND ACCESSORIES. 247 



mercury as it issues from the capillary will therefore cut 

 down the supply of gas. The instrument is thus rendered 

 more sensitive. 



By turning part B the inflow of gas can be regulated. 

 The instrument, therefore, permits regulation of the max- 

 imum inflow and minimum outflow of gas. Owing to the 

 large connecting tubes (a! and a") it is possible to have a 

 large supply of gas, and hence, the apparatus can be used 

 for regulating high, as well as relatively low tempera- 

 tures. 



The ordinary regulator, provided with a narrow cylin- 

 der or bulb filled with mercury, is not as delicate and as 

 responsive as might be desired. This is due to the fact 

 that the volume of mercury in the bulb is relatively small 

 and hence the rise and fall of the liquid in the capillary, 

 or upper tube is not marked, when only a slight variation in 

 the temperature occurs. Consequently, it is not possible to 

 maintain a very constant temperature with a plain mercury 

 regulator. A variation of one or two degrees, or even 

 more, must be expected. Moreover, the mercury in the 

 side-arm, since it is exposed to the air, will tend to counter- 

 act the action of the remaining mercury. This will especially 

 be the case, when there is a marked fluctuation in the tem- 

 perature of the room. 



The most delicate regulator is that which contains a 

 large volume of alcohol. An increase of a fraction of a 

 degree in the temperature will, in that case, cause a linear 

 expansion of the mercury in the capillary tube which will 

 be sufficient to shut off the gas supply. This fact is utilized 

 in the construction of the lower, or bulb portion (E) of the 

 author's regulator. As shown in Fig. 37, the capillary tube 

 is prolonged so as to almost touch the bottom of the glass 

 cylinder. The lower portion of the tube is provided with 

 a small bulb which serves to prevent air from entering the 

 cylinder when at any time the regulator is disconnected. 



