Evening star. [volume] (Washington, D.C.) 1854-1972, 1910-01-09

to the automatic cigar lighter and the hot
water bottle.
1T the bottom of which is packed some cotton
soaked in alcohol, ether, other inf1anmable
and easily evaporated hquld, at the top OF
which is small framework holding thin
vertical wire. When the top OF the tube IS
opened. in a short time the wire becomes red
hot and the alcohol vapor ignites therefrom.
The first explanation that would be thought
Of IS that the friction of the rapidly moving
vapor would make the wire become warm; but
on second thought this is seen to be too great
effect for such small amount OF energy
The real reason lies in the wire itself. In all
lighters now on the market the action IS praC-
tically the same. The wire Is either what IS
known as platinum sponge or some other metal
sponge that has the power of absorbing gases
rapidly Whenever anything absorbs gases,
that thing has made the gases occupy less
volume and whenever gases occupy less vol
ume they said to be compressed, and when
ever gases are compressed they invariably be-
come hotter, the amount of heat depending on
the amount of compression.
A great many things have the power of alb
soTbIng gases, charcoal being notable exam
pie Although charcoal absorbs good many
times its own volume of gases, it does not be-
come appreciablv hotter. 1t takes the metal
sponge for that for this absorbs hundreds OF
times its volume of gases and does 1t IN a
short time thus not allowing for the radiation
of the generated heat. So the little wire IS
generally heated to redness, ignites the wick
fed by the alcohol, and the thing is ready for
business.
To give some idea as to the intensity of heat
necessary for this, it will be stated that to red
heat a wire requires several hundred degrees.
When d gas is heated one degree centigrade it
expands almost exactly one Northumberland
seventy third of its volume at zero centigrade.
Conversely. when gas Is compressed one two
hundred and-seventy- third of its volume at
centigrade, it is heated one degree
Now suppose that gas IS compressed to one
fCS him Al
at zero centigrade it will be heated to two hun
dred and seventy-three degrees, an intensity
sufficient for our purpose. Thus the sponge has
to absorb only. saw one two three-hun-
dretfth of its volume of the supplied gas.
As to how it does this just what inherent
property enables it to DO it, is not well known.
The Hot and Cold Bottle
THE next thing mentioned is the hot and cold
water bottle the makers of the several varIe-
ties of which claim that it will keep any liquid hot
for three days and anything cold for two days,
vice versa. In this we have the whole theory
of the dissipation of heat: for cold means SIM
ply the absence of heat There are three ways
IN which heat may be carried from one body to
another, rather impaired by body to
another: by conduction by convection, and by
radiation. If all the precautions possible be
taken to prevent the action of these three
operations, little transmission of heat can take
place: so the hot liquid does not lose its heat
and the cold liquid does not receive heat from
the heated air bodies outside
The principle made Of is that of the De
War hask-all the bottles on the market to-day
being simply variations of this piece of scien-
tific apparatus The bottle is made to discount
far possible the three operations men,
toned. 1t consists of two layers of some pol
lshed metal with space between them that
has been exhausted of air as much as possible.
The two LAYERS are connected by lust as few
links as possible.
Taking up the three methods of transmission
IN succession, shall see how admirably each
one has been rendered inactive. BY conduction
of heat is meant the transmission of heat by
solid or something acting a solid in which
the medium itself does not move as to relative
situation of its parts. For instance in heating
Il poker in !; fire, one end is thrust in and be-
comes redhot, and in little while heat is con-
Quoted along the iron until the opposite end
becomes hot The same applies to teaspoon
IN cup of hot coffee This is why the bottle
referred to has as few connecting links between
layers as possible. as to make the contluction
of heat minimum. considering of course the
proper strength OF the bottle whole.
The next method is that of convection. By
this is meant the method of transmitting heat
by moving PARTICLES of liquid or a gas. Take
for instance the heating of water. The kettle
Is put over Il fire, and the bottom laver of water
is heated at once by the fire by conduction.
But heated liquid expands, and therefore be-
comes lighter than the cool liquid above; so it
has to rise. IL IS then displaced BY the cooler