THE CHEMICAL NEWS,
VOLUME XLII.
EDITED BY WILLIAM CROOKES, F.R.S., &.
No. 1075.—JULY 2, 1880.

ON THE LOWERING OF THE FREEZING-POINT
 OF WATER BY PRESSURE.*
By JAMES DEWAR, M.A, F.R.S,
Jacksonian Professor of Natural Experimental Philosophy in the
University of Cambridge.

THE Cailletet pump may be conveniently employed to
observe the thermal effe@s of compression on solid and
Quid substances. Before engaging in an investigation on
this subject, it was necessary to test the apparatus, and
especially the manometer. For this purpose it seemed, on
theorectical grounds, that observations on the lowering of
the freezing-point of water by pressure would be a severe
test of the accuracy of the pressure gauge, and the constancy
 of the records of thermo-junéions under pressure.
I am not aware of any quantitative experiments on this
subje¢t having been made under high pressures. Sir
William Thomson carried the proof of the accuracy of
Professor James Thomson's great theoretical discovery to
a pressure of 17 atmospheres.t The experiments of
Mousson (Pogg. Annalen, 1858) were not of a quantitative
tharadter, being merely intended to show that ice at a
temperature of —18° C. might still be liquefied by the
application of an enormous pressure. The following experiments
 appear to show that a convenient manometer
for very high pressures, based on the observations of the
Ireezing-point, may be easily constru&ed.
In all the following experiments the galvanometer,
moving to the negative side, showed a cooling effe& of the
junction inside the bottle. One division on the arbitrary
scale represented 1%, of a degree C. Two thermo-junctions
were used, made of iron-copper wires, which were in.
sulated by a covering of marine glue, the jun@ions them.
selves being covered with a thin layer of gutta-percha distolved
 in benzol.
One junction was placed in the bottle, to show the effe@
of pressure under different circumstances, the other being
kept outside at the constant temperature of melting ice.
Series 1.
One jundion, which was fixed in a brass flange with
marine glue, frozen in a test-tube containing boiled water,
was placed in the iron bottle and surrounded with water
at 0° C,, the bottle itself being packed round with ice.
The pressure was increased by 2g atmospheres at a
* A Paper read before the Royal Society June 17, 1880:
+ “The Effe@ of Pressure in Somers the Freezing.Point of
Water experimentally demonstrated.” Phil, Mag., 1850,

time. The galvanometer showed a deflection immediately
the pressure was applied, rapidly coming to rest at the
new position, and it remained perfectly steady as long as
the pressure was maintained.
The following is one of many series of experiments,
which agreed very nearly. Pressures were recorded by a
metallic manometer which had been checked on several
occasions. The records of the first 25 atmospheres pressure
 are not reliable.
Galvanometer zero} 1.
25 atmospheres= ~. 26 position on scale
50 ES = AT :
75 aiid
(5) =- 82
125 = —100
150 = —120
75 =—142
200 ”» =-163
225 ” - ~185
250 w ~~ =-203
275 » =—223
300 - = 243

Increase.
17
I9
20
18
20
22
21
, 22
: 18
n } ‘20
o 20

This represents a mean defle@tion of 19'7 on the scale,
being 0°18 of a degree C. for 25 atmosperes, or a lowering
of the freezing-point by. 21° C. for the total range of
pressure. The mean reduction for one atmosphere pressure
 is 0°0072°%
These experiments were afterwards repeated, with a
stronger pump, to 700 atmospheres. Exaély the same
mean defleGtion was observed, and the galvanometer moved
with the same regularity.
Series 11. ’
The jun&ion in the flange was placed in a piece of quill
tubing, open at top and bottom, in order to insulate it from
the sides of the iron bottle, and surrounded with water at
0° C. instead of ice, the iron bottle being afterwards packed,
as before, in ice, and the other jun&ion being outside in ice
and water.
This showed a very slight decrease of temperature on
applying pressure, the whole deflection for 200 atmospheres
being only about 4 divisions, or o'z of a degree C. This
agrees with Joule's experiments on the compression of
water, :
Series 111.
A mixture of finely powdered ice and water was placed
round the junction inside the bottle, which was as usual.