424 
DR. ANDREWS ON THE GASEOUS STATE OF MATTER. 
The pressure in atmospheres, as indicated by the air-manometer, on the gas in the car- 
bonic acid tube was given by the equation 
P = 
V 0 (l - 2 
760 ’ 
( 5 ) 
in which V 0 is the volume of the air at 0° and 760 millimetres, "Vj the observed volume at 
the temperature t, and q the difference of level (corrected when necessary for difference 
of capillary depression) of the surface of the mercury in the manometer and carbonic 
acid tubes, the negative sign applying to the case in which the mercury stands higher in 
the carbonic acid tube than in the manometer. 
The value of s, which is the ratio of the volume of the carbonic acid at the pressure^) 
(as indicated by the air-manometer) and temperature if to its volume at the same tempe- 
rature t ' under one atmosphere, is given by the equation 
'v 0 (i+o 
( 6 ) 
If we represent by Q the volume to which one volume of carbonic acid measured at 0° 
and 760 millimetres is reduced at the pressure^ and temperature t', we shall have 
It was manifestly impossible, at the great pressures employed, to surround the mano- 
meter and carbonic acid tubes with outer tubes of glass subjected internally to the same 
pressure, so as to equalize the pressure on both sides of the glass. Nor would any 
useful purpose have been attained if such an arrangement had been possible, as the 
thickness of the glass walls of the capillary tubes was never less than eight times the 
diameter of the bore, and any change in the capacity would be too small to affect sen- 
sibly the results. From a long series of experiments undertaken for the purpose of 
making a new determination of the compressibility of mercury, but not yet completed, 
I will give only the following result, as being sufficient for our present purpose : — A 
column of mercury 445 millimetres in length was exposed in a tube with a fine capillary 
bore to a pressure ranging from 5 to 110 atmospheres, at the temperature of 17°*60, the 
temperature scarcely varying 0°-01 during the experiments. The apparent change of 
volume for one atmosphere was found to be 
0-0000070. 
In a repetition of the same experiment at 18 0- 55, the result was 
0-0000072. 
From a series of experiments between 3*3 and 9 - 5 atmospheres’of pressure, Kegnault 
has calculated the absolute compressibility of mercury by. the aid of a set of equations 
which were furnished to him by M. Lame, and found it to be 
0-0000035. 
