1880.] 



On the Critical Point. 



195 



readings of its volume, were taken by means of a telescope placed 

 about one foot from the tube. The readings to tenths of divisions are 

 computed by eye, and are only approximately correct. 



The tube containing liquid was heated in a copper block, in which 

 a slit was cut open at the upper surface of the block, to permit 

 observations being taken. The block was covered with a plate of 

 glass and heated. It was found possible to keep the temperature 

 constant to within ^th of a degree for several hours by this 

 arrangement. 



Benzene was selected for the first set of experiments. While tem- 

 perature was kept constant, volume was altered, and the corresponding 

 pressure noted. The volumes are given in divisions of the tube, for 

 the bore was almost perfectly uniform, and the unavoidable error in 

 reading more than compensated any correction which might have 

 been made. 



The numbers refer to the curves on the accompanying woodcuts ; 

 the curves are isothermal. The pressure corresponding to each change 

 of volume forms the ordinate of the curve, and the volume itself the 

 abscissa. 



