OF DENSITY IN SATURATED VAPOURS. 
85 
Sulphurous acid (Faraday) 
Cyanogen (Faraday) 
Ammonia (Faraday) 
Arseniuretted hydrogen (Faraday) . . . 
Sulphuretted hydrogen (Faraday) . , . 
Muriatic acid (Faraday) 
Carbonic acid (Faraday) 
Nitrous oxide (Faraday), No. 2, p. 168 
Olefiant gas (Faraday), No. 1, p. 160 . . 
p=t 
A//-14-6671® 
11-194 J ■ 
P= 
\//-13-846'l® 
I 11-542 J‘ 
P = 
^ f a /#- 13 - 317 ]® 
I 11-050 J ' 
p — t 
Vt 
12-929 Y.^. 
10-264 / 
p — t 
^^^- 12-957 
9-878 
p = t- 
v'j;- 12-060 
9-413 
P=t 
p-=t- 
f 'C^-11-997 
[ 8-857 
I V'7— 8-936] 
1 11-604 J 
}• 
p = t 
f 10-352 
1 10-152 
While projecting different sets of observations of the same vapour, the attention is 
forcibly drawn to the tendency which the line shows to alter its inclination on the 
most trifling change of circumstances. This inclination depends on the value of the 
denominator h. It will be remarked that this constant is nearly the same for the 
vapours of ether and of water, also for a considerable number of the liquified gases. 
In fact the difference is not greater than might be caused by a slight want of purity. 
Even the specific nature of the vessel in which the observations are made seems mate- 
rially to affect the results. Dr. Faraday employed tubes of from one-fifth to one- 
seventh inch bore. I believe it will be found that the density is considerably less in 
these tubes than in larger vessels ; I have had proof of this in the case of ether heated 
in such tubes to 280°. The capillary attraction of the sides even at high pressures 
seems to affect the whole surface of the liquid, and to check the formation of vapour. 
We must not forget also, that Dr. Faraday’s temperatures are confessedly not so 
low as a correct thermometer would have indicated. The liquid he employed to 
measure the temperature was alcohol, and the degrees were graduated with the same 
capacity as between 32° and 212°. Now from the experiments that have been made 
on the expansion of alcohol by M. Gay-Lussac, and more recently by M. Munckb, 
it appears that the mean contraction between 32° and 212° is 6-2 thousandths of the 
volume at 173°, its boiling-point, and that this amount diminishes very sensibly with 
the temperature ; and if it continued to do so at the same rate from 32° to —100°, we 
should have Dr. Faraday’s —100° equal to less than —200° by the air-thermometer. 
It is clear that until the value of these degrees are known with reference to the 
air-thermorneter, the importance of Dr. Faraday’s observations cannot be fully 
estimated. 
