Omaha daily bee., 1895-12-14
MAKING CARBON boil,
This is What Happens when the Arc
Light is Burning.

The electric arc light, with it's intense
steady brilliancy, says the Literary Digest, Is
now so familiar an object that few stop tC
think how wonderful a thing 1t really is.
Here is light enough to illumine many square
yards nearly as well as daylight does. pro-
ceeding from the points of two little carbon
rods as large as ones finger. What is the
state of the carbon in that small spot? Prof.
S. p. Thompson, in a recent Cantor lecture
before the Society of Arts in London, tells us
that it has actually melted there, something
that was until recently thought impossible.
Moreover, he says that when the light Kisses
the liquid carbon is really boiling. The facts
that lead him to these conclusions are quoted
below from the report of his lecture that APP
pears In Industries and Iron:
Captain Abney had found the white surface
Of the luminous crater TO be Away OF an
equal degree Of whiteness, which obviously
means that it is always Of an equal degree of
temperature. The only thing that could ac-
count for there being a fixed temperature for
the crater surface was the fact that carbon
is at the surface in a state of Qualification;
that the carbon is evGporat!ng off from the
positive carbon into the arc or flame. At that
surface you necessarily must have the tenn
p~eTature at which carbon evaporates, just as
you cannot have the surface OF ice under or
binary conditions either hotter or colder than
the temperature which is taken as zero of
the Centigrade scale. My present view of the
physical state OF the arc crater Is that the
solid carbon below is covered with a layer or
film of liquid carbon, just boiling or evaporat-
ing off.
when Kissing takes place. a new state of
things is set up. If you watch a short, hiss
ing arc, you will see a column of light con-
centratlng itself on a narrow spot, and the
spot keeps moving about, and is very I'M
Stable in position as well as in the amount Of
light 1t gives out. The contracted spot from
which light seems to start pits deeper into
the carbon. Mrs. Ayrton made the observa-
tlon that the crater surface, after the arc has
been kissing, is found to be literally honey
combed. When the arc is Kissing you can
see little bits erupted out. and the Kissing
seems to be comparable to the Kissing which
takes place in water just when 1t is beginning
to Doll. III you have some water being heated
in such a way that there is not more than a
quantity OF heat given off from the
you have the water evaporating
quietly, but you cannot get more than a GER
tain quantity of heat given off per square inch
NJ top surface OF the water in that quiet way.
III you force more than a certain quantity of
neat to pass off per top square inch of the ]
water, you find the water begins to break |
up internally, and you have bubbles formed
below the surface; the surface breaks up, the
are thrown out, and you have a noisy
phenomenon. / think you will find there is
exactly the same kind Of difference between
he silent arc and the Kissing arc, as between
luiet evaporation and noisy boiling. There
s a sort of decrepitation, as the solid par
icles were being torn asunder to make way
or something coming out, when the arc is