CueMical News,
Nov, 22, 1878.

The Faraday Lecture. 245,
" that pressure appeared to be a more efficacious method
of condensation than cooling, inasmuch as a double pressure
 reduces the volume of the gas to one-half, whereas a
depression of temperature of 1° F. reduces the volume by
only z1;, the lowering of temperature, moreover, soon
attaining an impassable limit, It must, however, be
sspecially observed that, even in his first experiments,
Faraday made use of differences of temperature, if not to
iquefy the gases, at all events to distil and isolate the
liquids. Thus it was in the case of chlorine, for example,
and in that of ammonia, which he liquefied by heating
immoniacal silver chloride in a bent tube sealed at both
:nds, the liquid ammonia then distilling over and colle&ing
nn the empty branch of the tube, which was cooled to a
‘OW temperatures
Similar phenomena will be exhibited in the experiment
which I am about to show you, consisting in the liguefac-‘fon
 of cyanogen gas by heating cyanide of mercury in a
small glass tube terminated by a long capillary tube bent
n the form of the letter U. The figure of this curved
portion will be projected on a screen by the eledric light,
and in a few seconds you will see the liquid cyanogen
ollect in the bend.
Before leaving this part of my subje@, I would recall to
your attention two of Faraday’s discoveries resulting
rom the application of the principles just explained.
daving compressed coal-gas to twenty-five atmospheres,
Faraday, in 1825, discovered two important bodies, namely,
sutylene, a compound of great importance in a theoretical
point of view—and benzene—so named by Mitscherlich
several years afterwards—which in our own time has
secome the object of numerous and important applications,
and the pivot of an entire department of chemistry.
Another instance is aftorded by sulphurous acid gas
80), which was liquefied by Bussy in 1824, at the
ordinary atmospheric pressure by the effet of a cold of
2° to 15° below zero.
Whether we condense gases by pressure or reduce them
:0 the liquid state by diminution of temperature, the result
 of either method is to bring their particles closer
ogether. It would seem then, in accordance with Davy’s
view, that pressure ought to be more efficacious, as a
neans of condensation, than cooling. Nevertheless it is
10t so. The mere approximation of the particles of cerain
 gases does not suffice to effe& their liquefaction, and,
‘aoreover, the distances between the particles cannot be
liminished indefinitely by pressure alone. M. Natterer,
>f Vienna, has compressed oxygen, hydrogen, and nitrogen
“0 3000 atmospheres without effe@ing their liquefaction.
These gases, hitherto called permanent, cannot be
iquefied by pressure alone, and their liquefaction, which
has quite recently been effe@ed, is the joint effe@® of
strong pressure and a great degree of cold. This is the
important point, and I request your permission to offer
in this place a few explanations which will serve to place
it in its true light.
The impossibility of liquefying certain gases by pressure
 alone is in accordance with the ideas which are
current at the present day respecting the nature of aériform
luids, and likewise with a discovery made in England
within the last few years, on the continuity of the gaseous
and liquid states. I will explain myself briefly on these
‘wo points.
Daniel Bernouilli first enunciated the idea that gases
are formed of material particles, free in space, and animated
oy very rapid re@ilinear movements, and that the tension
of elastic fluids results from the shock of their particles
against the sides of the containing vessels. Such is the
origin of the kinetic theory of gases, which has been
revived since 1824 Ly Herapath, Joule, and Kronig, and
developed chiefly by Clausius and Clerk-Maxwell,
The law of Boyle and of Mariotte follows as a natural
:onsequence of this idea. Suppose a gas occupying a
certain volume, and composed of a definite number of
naterial particles—or molecules so-called—to be contained
a a closed vescel, such as the cylinder of an air-pump :

THE CHEMICAL NEWS,
VoL. XXXVIII. No, gor.

ON THE CONSTITUTION OF MATTER IN THE
GASEOUS STATE.*

LADIES AND GENTLEMEN,—1 esteem it a great honour to
address you within these walls, about which there still
aovers the ever fresh memory of him whose name we celebrate
 to-day, while we deplore his loss. Tam fully sensible
both of the great value of this honour and of the danger
:hat attends it, and I have need to shelter myself under the
authority of the great name of Farapav. I have, therefore,
 chosen a subject connected with his earliest
discoveries. The constitution of matter is a question of
the highest importance with regard both to physics and
to chemistry.
The word gas was introduced into science by Van
Helmont, who, at the beginning of the, seventeenth century,
 first pointed out, with some degree of precision, the
differences existing between certain aériform fluids. He
it was who first spoke of Gas silvestre, formed by the combustion
 of charcoal, and given off during the fermentation
of beer. To him, also, we owe the distindtion—which
kept its ground for two centurics—between gases and
vapours. He regarded gases as aériform fluids, incapable
of reduction to the liquid state by cooling, whereas vapours
require the aid of heat to maintain them in the gaseous
state, An important difference of constitution seemed,
therefore, to exist between these two kinds of aériform
fuid. This difference, however, 1s not fundamental, and
the distinction between gases and vapours has disappeared,
 in a theoretical point of view, being, in fad,
reduced to a simple question of temperature and pressure.
On March 13, 1823, Faraday, then a young man engaged
as chemical assistant at the Royal Institution, read before
the Royal Society a note entitled ““ On Fluid Chlorine.”
He had succeeded in condensing this gas to a liquid by a
process which has become classical. This process consists
 in heating in a closed vessel placed in a water-bath
crystals of chlorine hydrate. This compound, very rich
in chlcrine, is resolved at a gentle heat into chlorine and
liquid water, the quantity of which is not sufficient to
dissolve the whole of the chlorine. The latter is therefore
disengaged in great part in the state of gas, which accumulates
 in the small space remaining to it, and is liquefied
sy the pressure which it exerts upon itself.
On the same day Sir Humphry Davy read a note ¢ On
the Liquefa&ion of Hydrochloric Acid Gas,” which he
effected by decomposing sal-ammoniac with sulphuric
acid in a closed vessel. These researches were completed
by Faraday, who, on April 10 of the same.year, described
the liquefa&ion of a large number of gases, dire&ing his
efforts, by Davy’s advice, chiefly to those which are dense,
or very soluble in water, such as sulphurous acid, ammonia,
 sulphuretted hydrogen, carbonic acid. and orotoxide
 of nitrogen.
To enumerate the ‘special processes adopted in each
particular case would occupy too much time. We shall
therefore merely observe that the chief, if not the only,
means of condensation adopted in these experiments was
compression, that is to say, the reduétion of the gas to a
small volume, and that this compression-was exerted by
the gas upon itself, as it accumulated in the very strong
sealed glass tubes in which it was disengaged. Sir
Humphry Davv. in the note above cited. had remarked
* The Faraday Lecture, delivered before the Fellows of the Chemical
 Society, in the Theatre of the Royal Institution, on "Tuesday,
November 12, 1878, by Ad. Wurtz, Membre de Plastitut; Deven
Irdinaire de la Faculté de Médecine de Paris.