BULLETIN 532, U. S. DEPARTMENT OF AGRICULTURE. 
MEASURING APPARATUS. 
JEJL 
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Referring to figure 1, it will be noted that to measure the change 
in length of the specimen, crossbars of steel one-half inch square were 
cast in the concrete. They were placed 50 inches apart, center to 
center, and this was considered the 
(■ — .« j gauge length of the measurements. 
On each end of these bars a plug of 
steel with a rounded conical point 
was fastened, and micrometer meas- 
urements were taken between these 
points on each side of the specimen. 
Two readings were taken, so that 
unequal movements of the two sides 
of the specimen could be cared for 
by averaging the readings, thus ob- 
taining expansion or contraction 
along the center line. 
For obtaining the readings a spe- 
cial form of instrument (fig. 1) was 
designed and constructed in the labo- 
ratory. It consisted of a micrometer 
head reading to 0.0001 inch mounted 
at the end of a steel yoke. This 
yoke contained two steel rods five- 
sixteenths of an inch in diameter 
bolted to two end crosspieces, one 
holding the micrometer and the 
other a flat-ended steel pin. In tak- 
ing measurements the flat-ended pin 
was held in contact with the lower 
conical point of the specimen, and 
the micrometer was screwed down 
to contact with the upper conical 
point. During the initial readings 
electrical contact was used in order 
to read the micrometer to the nearest 
0.0001 inch. This, however, was dis- 
carded when it was found that read- 
ings of sufficient accuracy could be 
attained without it. In order that 
;,>:. change in the measuring instrument, due to wear or accident, 
might be detected, readings were taken repeatedly on a steel gauge 
bfix hung from the specimen. Before any reading was made the in- 
strument was hung alongside the specimen for a sufficient time to 
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