448 
DE. ANDBEWS ON THE GASEOUS STATE OE MATTEE. 
tain, that I have not ventured to use them. According to Regnault, the indications of 
the air-manometer are too high at 20 atmospheres ; according to Cailletet, they are 
- 8 - 0 - too high at 60 atmospheres, and only two i n error at 200 atmospheres. The appli- 
cation of these corrections would nearly remove in many cases the slight differences in 
the values of ^ and of s (1— p ) ; but I have thought it better to give only the direct 
results of experiment till the true corrections to be applied are accurately known. 
Another disturbing cause must be noticed, of little importance under the conditions 
of the foregoing experiments, but one which would seriously derange the results if the 
experiments had been carried down to pressures of 2 or 3 atmospheres. In all the 
tables I have given it has been assumed that, under a pressure of one atmosphere, 
one volume of the carbonic acid gas corresponds to one atmosphere of pressure. This 
assumption is not strictly legitimate, as it was shown long ago by Von Wkede that the 
density of carbonic acid compared with air is slightly less at one fourth of an atmo- 
sphere than at one atmosphere. In the absence again of complete data I have not 
attempted to correct for this disturbing cause, particularly as its influence would be very 
small at the pressures recorded in this paper. I hope to be able to supply hereafter 
both deficiencies ; but in the mean time it is certain that none of the general laws I have 
given will be disturbed by the application of the corrections referred to. 
I will now make a few observations on the properties of the gaseous state of matter. 
1. In the ideal, or, as it is commonly called, the perfect gaseous state, matter would 
obey implicitly the external forces which act upon it, the volume being always inversely 
as the forces externally applied. In this state it would neither offer resistance to change 
of volume *, nor, from the action of internal attractive forces, would it undergo a greater 
diminution of volume than that due to the external pressure. The characteristic pro- 
perty of this state is 
a=a , , 
where a is the coefficient of expansion at constant pressure, and a,' the coefficient of 
elastic force at constant volume. It has not been ascertained with certainty whether 
this condition of matter actually exists in nature, although, in gases which are at tem- 
peratures greatly above their critical points and at ordinary pressures, the deviation 
from it can only be discovered by the most exact experiments. Whether at higher 
temperatures or lower pressures the ideal condition is absolutely realized, or only inde- 
finitely approached, is a question which will perhaps scarcely admit of a direct experi- 
mental solution. 
2. In the gaseous state, as we observe it, there are two distinct causes of internal dis- 
turbance whose results are directly opposed, and, according to the nature of the gas and 
the conditions of pressure and temperature, sometimes the one and sometimes the other 
predominates. One of these disturbances is due to the action of internal forces tending 
* By resistance to change of volume is to he understood a resistance from internal causes whereby the gas 
undergoes a less diminution of volume under increased pressure than would occur in the case of an ideal guo 
obeying Boyle’s law. 
