Aug. a 1870 | 
carbonic oxide, and nitric oxide were 
sures than had previously been attained in glass tubes, and while 
under these pressures they were exposed to the cold of 
carbonic acid and ether bath, None of these gases exhibited 
any appearance of liquefaction, although reduced to less than 
son Of their ordinary yolume by the eombined action of cold and 
pressure Subsequently, in the third edition of Miller’s 
‘Chemical Physics,’’ published in 1863, a short account, 
municated by Dr, Andrews, appeared of some further results he 
had obtained, under certain fixed conditions pressure and 
temperature, with carbonic acid, These results constitute the 
foundation of the researches which form the general subject of 
submitted to greater pres- 
com- 
of 
the present article, and the following extract from the original 
communication of Dr, Andrews to Dr, Miller may here be 
quoted ;—‘*On partially liquefying carbonic acid by pressure 
alone, and gradually raising at the same time the temperature to 
88° Fahr,, the surface of demarcation between the liquid and the 
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 strice throughout its entire mass, At temperatures 
NATURE 
the | 
279 
sure of 400 atmospheres or more. A section, exhibiting all the 
details, is given in Fig. 1, Before commencing an experiment the 
body of the apparatus was filled with water ; the upper end-piece, 
carrying the glass tube, in which was the gas to be operated on, 
was firmly secured in its place, and the pressure was obtained by 
screwing the steel screw into the water chamber. In Fig, 2 the 
same apparatus is shown with the modifications required when 
the gas or liquid is exposed to very low temperatures under high 
pressure, The end of the capillary tube dips into a bach of ether 
and solid carbonic acid, under a bell j jar, from which the air may 
be exhausted. 
In order to estimate the pressure exerted in these experiments, 
a duplex or compound form of the apparatus was employed, as 
shown in Fig. 3: The two sides of the apparatus freely commu: 
nicate throug ad, so that on turning either of the steel screws 
the pressure is immediately transmitted through the entire appa- 
ratus, In the second tube a known volume of air is confined, 
and the pressure is approximately estimated by its contraction, 
Figure 4 exhibits the complete apparatus with the arrange- 
ments for maintaining the capillary tubes and the body of the 
apparatus itself at fixed te mperatures. A rectangular brass case, 
closed before and behind with plate glass, surrounds each capil- 
above 88°, 
into two distinct forms of matter could be effected, 
pressure of 300 or 400 atmospheres was applied. 
gave analogous results.” 
no apparent liquefaction of carbonic acid or separation 
even when a 
Nitrous oxide 
For his recent researches Dr. Andrews again selected carbonic 
acid as the substance for investigation. He devised for his ex- 
periments an apparatus, novel in construction, and well suited to 
exhibit the properties acquired by fluids under very varied condi- 
tions of pressure and temperature, The carbonic acid was con- 
tained in a glass tube, capillary in the upper and larger part of 
its length, and for the remainder, of the widest bore in which a 
column of mercury would remain without displacement when the 
tube was placed in a yertical position. A movable column or 
bar of mereury confined the gas to be operated on, This glass 
tube was secured by careful packing in a massive end-piece of 
brass, which carried a flange, by means of which a water-tight 
junction could be made with a corresponding flange, attached to 
a cold-drawn copper tube of great streagth. To the other end 
of the copper tube a similar end-piece was firmly bolted. The 
latter carried a fine steel screw, 7 inches long, which was packed 
With such care that the packing was capable of resisting a pres- 
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lary tube, and allows it to be maintained at any required tempe- 
rature by the flow of a stream of water, In the figure, the 
arrangement for obtaining a current of heated water in the case of 
the carbonic-acid tube is shown. The body of the apparatus 
itself, as is shown in the figure, is enclosed in an external vessel 
of copper, which is filled with water at the temperature of the 
apartment. ‘This latter arrangement is essential when accurate 
observations are made, 
The temperature of the water surrounding the air-tube was 
made to coincide, as closely as possible, with that of the apart- 
ment, while the temperatyre of the water surrounding the car- 
bonic-acid tube varied in different experiments from 13° C, ta 
48° C, In the experiments as they were performed, the mercury 
did not come into view in the eapillary part of the air-tube till the 
pressure amounted to about forty atmospheres. The volumes 
of the air and of the carbonic acid were carefully read by a cathe- 
tometer, and the results could be relied on with certainty to less 
than 1-20 of a millimetre or 1-500 of aninch, We must refer 
| the reader to the original memoir for an account of the details of 
the experiments, and of the numerous precautions adopted to 
secure accuracy. The object of the present article is to place as 
