line, anti at the bottom a bent tnlie is added. The brass flanged tube 

 E of the pressure cylinder had been previously cemented at 0, and 

 after a few drops of mercury luwc been brought into the large 

 reservoir, the tube is evacuated and tilled in a horizontal position. 

 When the tube has been tilled with pure hydrogen, it is put erect, 

 and the drops of mercury shut off the gas from the outer air. Then 

 the whole thing is placed in a waterbath of 15°. 5, while the differ- 

 ence in height of the mercury in the tubes ƒ and g is read. As 

 the volume up to the scalar divison, and the division itself too, has 

 been gauged, we now know the volume of a definite quantity of 

 hydrogen at about 1 atm. and the desired temperature. In order to 

 determine the pressure accurately, the pressure of the outer air 

 must of course also be determined, for which purpose the siphon 

 barometer is again used (p. 205). 



We can further dispense with the side tube, for it only served 

 to pi-otect the mercury at the bottom of the tubes against the water. 

 It is knocked off at g, and after the still remaining tube has been 

 entirely filled with mercury, the whole arrangement is put in the 

 pressure cylinder filled with mercury. The pressure cylinder is 

 closed, and connected with the hydrostatic press, which connection 

 is also in communication with the pressure balance. By means of a 

 rubber stopper a glass cylinder provided with a side tube at the 

 bottom and at the top is put round the projecting part, so that 

 water of 15°. 5 from a thermostat keeps the gas at the desired 

 temperature. The current was closed on the iron pressure cylinder; 

 then it passed through the mercury, and when the required height 

 had been reached it passed further through the platinum wire. By 

 means of the pressure balance the pressure at which the platinum 

 wire is reached, hence the pressure at which the gas volume is 

 diminished to the upper part, could be very accurately determined, 



§ 5. Corrections. 



Some corrections should be applied to the experimental results 

 obtained in the above described way. First of all in the g-auging 

 the volume is obtained in gr. of mercury of a definite temperature. 

 To reduce these values to the accurate volume in cm', two reduct- 

 ions must be applied. A reduction should take place to cm\ by 

 dividing the value in gr. of mercuiy by the specific gravity of 

 mercury at the temperatures of the gauging. The specific gravity of 

 mercury according to the Tables of Landolt and Börnstein was 

 used for this reduction. Further the compressibility of the glass of 



