GASEOUS AND LIQUID STATES UNDER VARIOUS CONDITIONS. 
47 
cause an abundant deposition of liquid, and the observations were made immediately 
after the application of the pressure. The slight deviations from that law under other 
conditions of the experiment he attributed to the hygroscopic affinity of the sides of 
the containing vessel, which condense a portion of the vapour and lower its tension 
below that due to saturation. As the result of all his observations, Regnault con¬ 
cludes that the law of Dalton may be considered to be theoretically true in the case 
of mixtures of gases and vapours, and that it would probably be in all cases verified 
rigorously by experiment if the mixed gas and vapour could be enclosed in a vessel 
whose sides were formed of the volatile liquid itself.* 
The only experiments, so far as I know, on the effects of pressure upon mixtures of 
the ordinary gases are a few recorded by Regnault on mixtures of atmospheric air 
and carbonic acid, and of hydrogen and sulphurous acid. The observations were made 
within limits of pressure extending from two-tliirds of an atmosphere to two atmo¬ 
spheres, and the results indicated that within these limits the compressibility is inter¬ 
mediate between that which each gas, if isolated, would exhibit for the same variations 
of pressure, t 
The result of these experimental investigations is to confirm, with one exception, 
the law of Dalton for all cases of mixtures of gases or of vapours, or of gases and 
vapours which have no chemical action upon one another. The exception referred to 
is that of a mixture of vapours derived from liquids capable of dissolving one another, 
and in presence of the compound liquid. To such a case the law of Dalton, as 
originally enunciated, is clearly inapplicable, since chemical affinities come into play 
which disturb the result. The diminution of volume and disengagement of heat which 
occur when water and alcohol in the liquid state are mixed prove, as Gay Lussao 
long ago pointed out, that there is a well-marked affinity between those liquids, 
resulting in the formation of a chemical compound, and that it is the tension of the 
vapour of this compound which is actually observed. 
It would, however, be a hasty inference to conclude that the law of Dalton has 
been fully established by experiment, the more so as in none of the investigations to 
which I have referred was the pressure carried beyond two atmospheres. As the 
apparatus described in my former communications was well adapted to this inquiry,| I 
* ‘ Memoires cle l’Academie des Sciences,’ vol. 26, 1862, pp. 680-696. 
t Ibid., p. 258. 
X The following foot-note occurs in the earlier draft:— 
“ I wish here to supply an omission in my former paper, and to explain, for the information of 
future experimenters, the mode of packing*the screws and of connecting the glass tubes with the metallic 
flanges. In fig. 3 of the plate accompanying this paper a section of the steel screw is shown, from 
which it will be seen that the screw enters a female screw in the flange (fig. 7) for about half an inch, 
and afterwards a leather packing of more than one inch in length. This packing is formed of a number 
of circular disks of leather punched through in the centre and saturated in vacuo with melted lard 
After each disk is introduced it is pressed firmly into its place in the flange by hammering lightly with 
a wooden mallet upon an iron bolt, which fitted loosely the cylindrical cavity. The flange, w r hen 
