Intelligence and Miscellaneous Articles. 



531 



heat sufficiently to have its volume, considerably altered by any 

 difference between, the atmospheric pressure and that within the 

 bulb. Thus it is important to know at the end of an experi- 

 ment to what extent, if any, the volume of the bulb may have 

 changed, as any such change must be taken into account in 

 calculating the temperature. 



The usual method of volumetry by weighing with water is long 

 and arduous, involving as it does the takiug apart of the apparatus. 

 Below is given a simple and sufficiently accurate method of 

 calculating the volume at any time without disconnecting the bulb. 

 In addition to the usual apparatus it is only necessary that the 

 manometer tube in which the air is confined be graduated for 9 or 

 10 centim. from the top, so that the volume of air in the tube 

 may be computed. 



In the figure, B is the bulb, PP 

 a capillary connecting tube, T the 

 graduated manometer tube, the gra- 

 duated portion of which is about 

 1 centim. in diameter, connected in 

 the customary manner by flexible 

 rubber tubing with a reservoir. 

 The scale in question is shown at 

 T and is graduated in 0*1 centim. 

 beginning with the fiducial mark. 



Assuming the whole apparatus to 

 be at constant temperature during 

 the operation, the required volume 

 V is easily found as 



P,-P« 



when v 2 and v l are volume excesses measured by means of the 

 scale on T, corresponding to pressures P 2 and P x respectively. 



It will be observed that "V is not the volume of the bulb alone. 

 Still, since the bulb is the only variable factor, the above formula 

 indicates what change it may undergo. 



The following is an example of a number of observations 

 leading to the volume of a glass bulb used ; in each case the 

 first reading is combined with the third, the second with the 

 fourth, in finding the values of P 2 i\, — ~P 1 v l and P — P v . 



Beduced atmospheric pressure = 74- 7b' centim. 



P(cm.) 



v(e.c.) 



V(c.c) 



75-17 



0-16 



239-0 



74-63 



1-80 



241-1 



73-79 



4-47 





73-27 



o-iu 





