HYDROGEN. 
posed, the iron attracts its oxygen, and hy- 
drogen gas issues from the extremity of the ' 
tube. 
This process is a troublesome one, and 
by the agency of an acid, water is decom- 
posed as rapidly by iron or zinc, at a natu- 
ral temperature. Zinc affords the hydro- 
gen in the greatest purity. One part of it, 
in small pieces, is put into a retort, or a 
bottle with a bent tube adapted to it ; 
two parts of sulphuric acid, previously 
diluted with five times its weight of 
water, are poured upon it, an effervescence 
is immediately excited, hydrogen gas es- 
capes, and is to be collected in jars filled 
with water, and placed on the shelf of the 
pneumatic trough. Its disengagement con- 
tinues until the zinc is dissolved. Iron may 
be employed in place of zinc, but contain- 
ing generally a little carbon, which is dis- 
solved by the hydrogen, it affords a gas less 
pure. Muriatic acid serves the same pur- 
pose as sulphuric acid, but must be diluted 
with only twice or three times its weight of 
water. 
In the experiment, the hydrogen gas is 
derived entirely from the decomposition of 
the water, the oxygen of which is attracted 
by the metal. That the acid suffers no de- 
composition, is proved by the liquor at the 
end of the experiment, being capable of sa- 
turating as much of an alkali as the quantity 
of acid employed would have done in a 
pure state. The agency of the acid was 
formerly explained, on the absurd doctrine 
of disposing affinity,— that it had no attrac- 
tion to the pure metal, but to the oxide of 
the metal; that to satisfy this affinity, it 
caused the oxidation of the metal at the ex- 
pence of the water, and then combined 
with the oxide thus formed. In conformity 
to Berthollet’s speculations, it may be re- 
ferred to the affinities of the acid to iron, 
and to oxygen, conspiring with the affinity 
of iron to oxygen : these, co operating, pro- 
duce a ternary combination, while the hy- 
drogen gas is disengaged. 
Hydrogen gas is permanently elastic. 
When collected over water, it is observed 
to have a peculiar smell, slightly fetid, 
which is not so perceptible when it is col- 
lected over quicksilver, and which is lost 
when the gas is exposed to substances which 
powerfully attract humidity. It is not the 
only substance in which water appears re- 
quisite to develope odour. 
This is the lightest of the gases, and in- 
deed the lightest substance whose gravity 
can be ascertained by weighing. Its spe- 
cific gravity varies considerably, according 
to its state with regard to humidity. When 
it has been transmitted through water, or 
has remained for some time exposed to it, 
it, is about ten times lighter than atmosphe- 
ric air; when it has been received over 
quicksilver, and exposed to any substance 
which attracts water strongly, as quicklime, 
it is nearly 13 times lighter, or atmosphe- 
ric air being 1,000, hydrogen is 84. It* 
specific gravity in this state, water being 
1,000, is stated by Lavoisier at 0.0946. 
100 cubic inches weigh 2.613 grains. It is 
from this levity, that it was applied with 
success to the construction of balloons ; a 
varnished silk or linen bag, filled with it, 
having a specific gravity so much less than 
atmospheric air, as not only to rise in th« 
atmosphere, but also to elevate an addi- 
tional weight. 
The chemical property by which hydro- 
gen gas is most eminently distinguished, is 
its great inflammability. When an ignited 
body is approached to it, in contact with 
the atmosphere, it is immediately kindled, 
and continues to burn while the air is ad- 
mitted ; if previously mixed with atmosphe- 
ric air, and a burning body approached to 
the mixture, or an electric spark sent 
through it, it instantly inflames with deto- 
nation ; and when it has been mixed with 
oxygen gas, the detonation is more violent. 
When burning at the extremity of a capil- 
lary tube, on bringing a wide tube over the 
flame, a singular phenomenon, accidentally 
observed by Dr. Higgins, is produced, that , 
of sounds of various tones, which vary in 
acuteness and strength, according to the 
width, the length of the tube, and the kind 
of substance of which it is formed, owing, ap- 
parently, as Picket and De la Rive have 
explained it, to the vibrations excited in 
the matter of the tube by the rapid expan- 
sion and condensation of the watery vapour 
near and around the flame, and which, re- 
gulated and equalized by regular reflections 
from the sides of the tube, constitute a mu- 
sical sound. (Nicholson’s Journal, 8vo. 
vol. i. p. 129 ; ibid, vol. iv. p. 23). 
Though hydrogen gas be inflammable, it 
is incapable of supporting the combustion 
of other inflammables. If a burning' body 
be quickly immersed in it, it is immediately 
extinguished. 
This gas is incapable of supporting ani- 
mal life by respiration ; an animal immersed 
in it is soon killed. At the same time, it 
