SAMPLING AND TESTING HIGHWAY MATERIALS. 
45 
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equal distances from the bottom and serve for measuring the charge of material, 
which is 240 c. c. The thermometer e is used to ascertain the temperature of the ma- 
terial to be tested. The vessel a is surrounded by a brass jacket,/, which holds the 
material used as a heating bath, either water or cottonseed oil, according to the tem- 
perature at which the test is to be made. A tripod, g, serves as a support for the 
apparatus and also carries a ring burner h, by means of which the bath is directly 
heated. The measuring cylinder of 100 c. c. capacity, which is sufficiently accurate 
for work with road materials, is placed directly under the outflow tube. 
As all viscosity determinations should be compared with that of water at 25° C, 
the apparatus should be previously calibrated as follows: The cup and outlet tube 
should first be scrupulously cleaned. A piece of soft tissue paper is convenient for 
cleaning the latter. The stopper is then inserted in the tube and the cup filled with 
water at 25° C. to the top of 
the projections. The meas- 
uring cylinder should be 
placed directly under the 
outflow tube so that the 
material, upon flowing out, 
will not touch the sides, and 
the stopper may then be re- 
moved. The time required 
both for 50 and 100 c. c. to 
run out should be ascer- 
tained by means of a stop 
watch, and the results so ob- 
tained should be checked a 
number of times. The time 
required for 50 c. c. of water 
should be about 11 seconds 
and for 100 c. c. about 22.8 
seconds. 
Bituminous road mate- 
rials are tested in the same 
manner as water, and the 
temperature at which the 
test is made is controlled 
by the bath. The material 
should be brought to the desired temperature and maintained there for at least three 
minutes before making the test. The results are expressed as specific viscosity 
compared with water at 25° C, as follows: 
_ . _ . . _ _ seconds for passa ge of given volume at A°C. 
Specific viscosity at A <-= se conds for passage of same volume of water at 25° C. 
28. DETERMINATION OF PERCENTAGE OF RESIDUE OF DESIRED 
PENETRATION. 
Fifty grams of the oil are placed in a 3-ounce deep, seamless tin box; the box is 
placed in a sand bath and heated over a Bunsen burner. A thermometer is suspended 
in the oil, the bulb not touching the bottom of the box. The temperature of the oil 
is kept at from 249° C. (480° F.) to 260° 0. (500° F.), and the oil is stirred from time 
to time with the thermometer to prevent overheating in any part. Depending upon 
the nature of the oil, as usually indicated by its flash, consistency at 25° C. (77° F.) 
and specific gravity, the operator can with experience tell about what percentage it 
will be necessary to evaporate before cooling and taking a penetration of the residue. 
Ss*. 
Fig. 23.— Engler viscosimeter. 
