576 
DE. ANDREWS ON THE CONTINUITY OE THE 
88°Fahr., the surface of demarcation between the liquid and gas became fainter, lost its 
curvature, and at last disappeared. The space was then occupied by a homogeneous 
fluid, which exhibited, when the pressure was suddenly diminished or the temperature 
slightly lowered, a peculiar appearance of moving or flickering striae throughout its 
entire mass. At temperatures above 88° no apparent liquefaction of carbonic acid, or 
separation into two distinct forms of matter, could be effected, even when a pressure of 
300 or 400 atmospheres was applied. Nitrous oxide gave analogous results”*. 
The apparatus employed in this investigation is represented in Plate LXIII. It is 
shown in the simple form in which one gas only is exposed to pressure in figures 1 & 2. 
In figure 3 a section of the apparatus is given, and in figure 4 another section, with the 
arrangement for exposing the compressed gas to low degrees of cold in vacuo . In figures 
5 and 6 a compound form of the same apparatus is represented, by means of which two 
gases may be simultaneously exposed to the same pressure. The gas to be compressed 
is introduced into a tube (fa) having a capillary bore from a to 5, a diameter of about 
2-5 millimetres from b to <?, and of 1-25 millimetre from c to f. The gas carefully dried 
is passed for several hours through the tube open at both ends, as represented below. 
cfl. C 
. 
b 
CL 
e d. 
m, rb 
7> 
a 
e r7. 
7, 
- 
— ' 
The presence of a column of water of two metres in height was necessary to maintain a 
moderate stream of gas through the fine capillary tube. In the case of carbonic acid, 
the gas, after passing through the apparatus, was made to bubble by means of a con- 
necting-tube through mercury, and a portion was collected from time to time, in order 
to ascertain its purity. The current was continued till the residual air, after the action 
of caustic potash, was reduced to a constant minimum. In repeated trials I found that 
in the complicated arrangements I had to adopt, the residual air could not be reduced 
to less than from -g^g- to two the entire volume of the carbonic acid. Even after con- 
tinuing the current for twenty-four hours this residue appeared ; and in discussing some 
of the results obtained by exposing the gas to high pressures, the presence of this small 
quantity of air must be carefully taken into account. The capillary end at a was then 
sealed, and the other end was also closed, and afterwards introduced under a surface of 
pure mercury contained in a glass capsule. The lower end, while under the surface of 
the mercury, was opened, and heat applied so as to expel a little of the gas. On cooling 
contraction occurred, and a short column of mercury entered. The capsule and lower 
end of the tube were then placed under the receiver of an air-pump, and a partial 
* Miller’s ‘ Chemical Physics/ 3rd edition, p. 328. 
