SPECIFIC GRAVITY OF NITROGEN, ETC. 
341 
force of that to which they are attached; and that alternate 
spaces of stronger and weaker attraction would succeed each 
other from the centre outward; it was noticed that Dr. Thom- 
son, by careful and repeated experiments, has ascertained the 
specific gravities of the following gases to be these: — viz. 
nitrogen f J, oxygen y, hydrogen T y T) ana< chlorine 2%, and by 
examining the experiments of the best chemists it will be 
found that no numbers can be fixed on nearer the truth than 
these. Nitrogen is the most permanently gaseous, and seems 
to be the most elementary in its character; the experiments 
of chemists nearly agree as to its specific gravity as follows: — 
.9691 Biot and Arago. 
.973 Thomson. 
.976 Berzelius and Dulong. 
.9705 Thenard. 
The mean of the first three exceeds f J- by only of an 
unit, and the mean of all four falls short of it by the same 
very minute quantity. Two volumes nitrogen and one 
oxygen make two of protoxide of nitrogen, the specific gravity 
of which Berzelius found to be 1.5273; from this and the 
above we have for the specific gravity of oxygen, — 
1.1164 Biot and Arago. 
1.1086 Thomson. 
1.1026 Berzelius and Dulong. 
1.1136 Thenard. 
The first and last are a little more than and the two others a 
little less: the direct experiments of Dr. Thomson give 1.1117; 
these considerations afford sufficient evidence that y is either 
exactly the true specific gravity of oxygen, or that it scarcely 
differs from it at all. The same appears from other consider- 
ations. All gases have a degree of cohesion, and were it not 
for the pressure, would be held, between their attractions and 
the pressure of ethereal matter, in a state of equilibrium. 
Nitrogen forms the basis of the atmosphere, probably, because 
of its large sphere of repulsion; its proportionate quantity to 
vol. iv. — no. iv, 44 
