TRAVELERS’ HOTEL

THOMAS RICKSON, Proprietor

Licensed Premises

WESTVIEW, B.C.

e same lens. No expert evidence is neces-
ry as the results are self evident. A plaster
1st made in this manner with the pieces
ssembled properly will prove of great value
) the Court in arriving at a conclusion, and
‘ill be of material aid in corroborating any
ther evidence available.

As previously mentioned, the instances
there a perfect “fit” can be made are
slatively few, but this should not discour-
ve the investigating officer from saving all
he pieces of glass found at the scene of an
ccident, as the chemist can furnish a great
eal of valuable information, even if the
‘eces do not fit together physically.

Glass fragments are compared with each
ther in a number of different ways by the
hemist. Hardness is one of the factors
ometimes resorted to. This may be accom-
lished by attempting to scratch materials
f varying degree of hardness, until one is
ound that can be scratched by the piece of
lass under test. The other sample is then
ested in similar manner, and the results
ompared. Specific Gravity is an important
actor. This is the relative weight of the
lass to the weight of an identical volume
f water. It can be accomplished by the
well known displacement test in a specifi
yravity bottle. However the chemist use
much more refined technique. There i
Iso the Refractive Index of the glass which
sas to be taken into consideration. This is
he ability of the glass to bend a ray of light.
ft may be roughly determined by placing
he glass fragments in a bottle with a liquid
sf a known refractive index close to that
of glass generally. The glass pieces can still
ne seen in the bottle. Then a second liquid
with a different refractive index is carefully
added, little by little until the glass seems

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to disappear. This will indicate that both
the glass and the liquid have the same re-
fractive index. By computing the relative
amounts of the two liquids used in making
the test, the refractive index of the glass is
obtained. In actual practice, however far
more accurate methods are employed by the
chemist as he determines the Refractive In-
dex of the sample under test to four decimal
places. Fluorescence is also sometimes
taken into consideration. The glass is sub-
jected to ultra violet light. Different com-
ponents in the glass vary the intensity and
colour of the fluorescence. If two samples
do not show the same degree and colour of
fluorescence, then.they can be readily elim-
inated. Last, but certainly not least, is the
Spectrographic Analysis of glass. The
chemical composition of the glass is defin-
itely ascertained by this method, even to
traces of impurities which might be present
in the original ingredients. The percentages
of the different components can also be

“measured. To put it simply, the spectro-

graph vaporizes a tiny fragment of glass
in an electric arc. The light emitted from
the glass vapours is then broken up into a
a spectrum and photographed. By compar-
ing known standards with the photographic
negative both a quantitative and qualitative
analysis is made at the same time. These
tests are applied to both samples and the
results compared. By these means the
Analyst can definitely tell whether or not
two samples of glass are identical in all re-
spects.

To illustrate the diversity of components
and impurities found in specimens of glass,
Mr. G. C. B. Cave, Chief Analyst and
Director of the Department of Mines Lab-
oratory at Victoria, B. C., supplied the
following list which he says is by no means
all inclusive :—

Pacific Coast Truck
Loggers Limited

x

P.O. BOX 523 PHONE 7791

*

POWELL RIVER, B. C.

Proprietor: V. RITCHIE P.O. Box 882
WILDWOOD MOTORS
Phone 4391

Dealers for
DODGE and DE SOTO CARS
DODGE and INTERNATIONAL TRUCKS

Powell River, B. C.

Major constituents—

Lime Soda

Potash Silica

Lead Barium

Boron Beryllium

Zinc Thalium
Minors and impurities—

Iron Aluminum

Arsenic Managanese

Strontium Magnesia

Chromium Molybdenum

Copper

As there is so little generally known
about the subject of glass fractures, perhaps

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R= RADIAL

STRIATION DENOTES SOURCE OF FORCE
CRADIAL)

C= CONCENTRIC FRACTURES |
do.

9
SHATTERING DIRECTLY BELOW \MPACT POINT.

37 20

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