Evening public ledger. [volume] (Philadelphia [Pa.]) 1914-1942, 1920-09-02
THE LIGHT THAT LIES
That 10, u Lies About the Candle
power That Makes II and Uses
Things Called British Thermal
Units Instead -
NOBODY has made any violent ob}ection

standard for gas instead Of the old candle
| power standard. The propositions In bofl
places have gone through Without murmu
the to tSs spils change .ys apparently
body is satisfied. But. before the What
Do You Know editor thinks Of II, Il 4
as well to spring three questions here. The!
are:
!. First r What is candepower and how
Second. What is a British thermal unit
and how do you recognize 1t when yor
Third. What is the reason a mantle give
brighter light with poorer gas, than bart
flame burner with good gas2
Probably not one man In q hundred oi
all who have SO readily assented to tn,
changed systems can answer any one oi
these questions. Yet, without a knowledge
OF all three. how can we decide whether We
favor the new standard or notI ~
Under the old lease the contract between
the y. g.. !. and the city called for gas that
would give twenty two cendlepower
flame In the open burner with gas flowing
at hve cubic feet per hour. Under the new
gas lower In illuminating power, but suf1-
GENTLY high in British thermal units to
give the twenty-five power with a mantle.
LNRsT, Aen, as to what candlepower Is.
" The standard candle used by illuminating
engineers the world over is supposed to be
made of pure spermaceti, to weigh one
sixth of pound and to burn at such rate
that 12O grains of the sperm oil shan be
consumed each hour. These are all arbi-
trary measures, OF course: but they have
been agreed upon by scientists and the light
given by such d candle Is the standard
candlepower Of today.
But we no longer use the old sperm oil
candle. In measuring electric lights, spe-
cial electric lights accurately compared with
lie ~ onSlla la A. aAI tv
delphia the brightness of the gas is meas
ured by comparison with a ten -candlepower
lamp burning vaporized pentane, a product
Of petroleum. ~
TT is a simple enough problem to de-
L termine the candlepower Of any doubtful
light. Everybody knows that II you put
n spot of grease In the center of a piece of
paper and hold it up between you and
light the grease spot looks brighter than the
rest Of the paper; 1t seems to permit the
light to shine through il. II, on the other
hand. you and the paper are on the same
side Of the light the grease spot looks darker
than the paper.
So we take our standard light and put it
up. set the paper with the grease spot any
known distance from it and. on the other
side Of the paper, set up the light to be
tested. We watch the grease spot and move
the lights until grease spot and paper look
Just the same. This proves that the amount
Of light falling on one side is exactly equal
to the amount falling Oh the other.
Now. in scientific jargon, the intensites
OF these lights vary with the square of
their distances from the object. In other
words. II the doubtful light in the expert
ment is twice as far away from the paper
as the standard light. its brilliance is two
times two, or four times the brlliance Of
the standard light. So. II it is three times
as far away when the grease spot disap-
pears. its brilliance Is three times three, or
nine times that of the standard. ...
uERE in Philadelphia the Bureau of Gas
i Il has two stations for making constant
tests OF the gas supplied to tie city. Under
the direction OF Or. y. Wiley Thomas, cL:es
OF the bureau. STAG Of experts :.ake -egv-
la. readings o. this Instrument. wS:ca is
Enowr as SIase. psotoEere: Il psysica!
laboratories.
The substitution of British ther.na! units,
however. calls into play another instrument
known as calorimeter with the accent
on the ''rim.' BY the wny). Now British
thermal unit--kDOwn among engineers as a.
B. I. us not nearly so formidable as
its name sounds. 1t Is simply the amount
of heat required to raise one pound of water
on" degree Fahrenheit. So, II we have an
instrument that will tell us the weight of
water. the rise in it's temperature and the
amount of gas burned to make that rise, it
Is an easy matter to calculate the number
of gas.
These measurements are made by the in
strument used in the testing stations here,
one station being situated at Seventeenth
street and Passyunk avenue and the other
at Richmond and Ann streets. These lOca-
tions were chosen because each is just about
a mile from the gas works which supplies
it and therefore gets the average city gas.
60 WE come to the mantle and the aues-
. tion of what makes it burn so brightly.
Oddly enough. the first thing that Is done
with a mantle attachment is to take all Of
the Illuminating power out of the gas In
order to make 1t illuminate more brightly.
This sounds like paradox, but it Is really
merely changing the form of the energy that
is in the gas aud then rechanging it.
Every mantle is mounted on little
tube contrivance that Is a miniature Bun
sen burner. This tube has air holes in 1t
and it's object is to mix air with the gas
so as to get the most perfect combustion and
thus obtain the maximum amount of heat.
1t works on much the same principle as the
carburetor on fivver, which is simply
an apparatus for obtaining the correctly
mixture of air and gasoline
vapor.
The mixture in the Bunsen burner burns
with a blue, or almost invisible. flame much
like the painters torch. and many a man
has burned q hole In the legs of his over
dl1s WIN DcChuSt lie tOulu not see tnP
flame.
So the Bunsen burner gives US an in
tensely hot flame To start ,with--a flame,
that is, which contains the maximum mum
Der of b. 7. US.
CCIENTISTS have discovered that there
~ are certain substances which. when
heated to incandeseence, will emit brill
liant white light, and some Of these sub
stances will do this at comparatively
low temperature. The gas mantle utilizes
two of these substances.
The blue flame from the Bunsen tube
raises the meshes of the mantle to this
white incandescence, and they give off this
brilliant illumination, and 1t does not mat.
ter what the gas is made Of so long as the
required amount of heat Is obtained. In
this way the purpose Of the gas is only to
heat and not to light. The substances In
the mantle do the lighting.
In the making Of these mantles the great
est ingenuity has been shown, and they are
a triumph of the imagination and cleverness
of scientists.
First, the mantle is woven of plain cotton