Evening star., 1938-09-22
OF STARS,
MEN AND ATOMS
Notebook of Science Proaress
in Field, Laboratory
and Study.
By THOMAS r. HENRY.

A man apparently weighs more on
hot than on cold day.
Evidence to support this has just been
presented to the American Chemical So
ciety by DR.. Francis w. Power of the
staff Of Fordham University
The little balance used by a micro
analyst, DR.. Power pointed out, will de-
tect a weight as small as a fifty
thousandth of postage stamp. So deli
cate an instrument naturally will be very
sensitive to temperature changes, and
some years ago German chemist point
ed out that if one arm of this balance
were increased in length. due to unequal
heating, by an amount equal to a hun
dredth of the wave length of ultra
violet light, the microbalance would be
able to detect this as an apparent in
crease in weight.
DR.. Power set out to check up on this,
but 1t involved detecting an increase in
length Of from only one to two ten
millionths of an inch. One of the meas
urements required was that of the area
Of the balance beam. The Fordham
chemist resorted to an old trick Its area
was taken from a life-sized photograph
from which little paper balance beam
was cut out with sharp scissors. BY COM
pairing the weight of this paper beam
with the weight on known area of the
Photographic paper, the weight of the
beam could be calculated by proportion.
L have made the necessary measure
ments OF the apparatus actually used and
have performed the corresponding calcu-
lations," says DR.. Power 1t turns out
that If the temperature inside the bal
ance case is increased by one centigrade
degree, the tubes used in the carbon
hydrogen analysis will exhibit apparent
gains in weight, which are easily de-
tectable on the sensitive balance used
and which in the case of the carbon tube
amounts to significant error.
The obvious remedy would be to in
stall a sensitive temperature control sys-
TEN In the weighing room, but in most
cases this would be a very expensive
proposition. The other and much sim
pier remedy is to weigh the tubes against
weights having nearly the same density
as beam could be calculated by propor-
ton. This is an old trick often resorted
to by mathematicians and engineers
when they have to calculate the area
under some irregular mathematical
curve. The upshot of the calculation was
that the German chemist was very nearly
right; the minimum detectable weight
corresponded to about one-fiftieth of a
wave length of violet light instead of a
hundredth as he had figured, but as the
difference amounted to only about ten
milllonth of an inch he wasn't very far
off. The balance is still long way from
being a hay-scales!"
Says DR.. Power: when you weigh
yourself on regular platform scales with
brass weights on the arm of the scales,
both you and the weights are buoyed up
by the air: but since the body occupies
eight or nine times as much space as do
the weights this lifting effect is COR
reSpondingly greater on the body than
1t is on the weights. Archimedes is said
to have jumped out of his bathtub crying
Eureka when he discovered that body
immersed in a fluid is buoyed up by an
amount equal to the weight of the fluid
which it displaces The buoyance effect
OF given volume of lighter warm air
will be less than that exerted by the
same volume of heavier cold air.
III We visualize this effect as a slight
upward push or the body and a much
smaller upward push on the brass weights
we can see that diminished buoyancy
on both. due to higher temperature and
decreased air density will result in q
considerably weakened upward push OF
the body as compared to the correspond
ing push due to cold air. The weights,
however, occupy so little space that the
upward push of the air will be about the
same no matter what the air temperature
is. The tubes themselves thus causing
the buoyancy effect to be the same on
both and a differential effect of zero.
The current practice is to use small glass
bottles filled with BIB shot to counter
poise the tubes. and on account of the
preponderance of lead in these counter
poises the differential effect of air buoy
ancy is exaggerated as compared to what
it would be if the counterpoises were
made entirely of glass. which is the prac-
tice recommended in this paper.
Experiments were conducted on this
diferential buoyancy effect by perform
ing the weighings in room at normal
temperature and then repeating the pro-
cess several hours later after the room
had been uniformly heated up about 80
degrees F. by electric heaters. Oddly
enough. the observed effect was not very
uniform on repeated experiments but was
usually two or three times as great as
that calculated. These experiments are
being continued to see if any reason can
be assigned for this Unexpectedly large
effect. This is what is known as learn
ing more and more about less and less"