- EXAMINATION OF BITUMINOUS ROAD MATERIALS, 21 
DISTILLATION TEST. 
EQUIPMENT. 
1 250 cubic centimeter Engler distillation flask. 
1 chemical thermometer reading from 0° ©. to 400° C. 
1 short condenser, with rubber tubing. 
6 25 cubic centimeter glass cylinders, graduated to 0.2 cubic centimeter. 
liron ring support (ring 7.5 cm. in diameter). 
1 iron tripod. 
’ 1 burette clamp. 
1 tin shield. 
1 pinchcock. 
2 Bunsen burners, with rubber tubing, 
1 quart tin cup, seamless. : 
1 pint tin cup, seamless. 
1 rough balance, capacity 1 kilogram, sensitive to 0.1 gram. 
1 analytical balance, capacity 100 grams, sensitive to 0.1 milligrams. 
METHOD. 
The Engler flasks for this test should meet the following require- 
ments: 
IDMAUTAGSAET? OE LON ove Eg eae cst a ln de og pe ee a ce a 8.0 ¢c. m. 
emmerGhimOiMe Cheseae par hes ob ree ie As Wa So ee See a dk 15. 0 c. m. 
Daammeveioieme@ ket: qa cine ye Ne 7 Cone 
J (SEVBATIN, Cue. ULL DULG GORE ENG a UI a ea a en cee ee aia eg 15.0 ¢. m. 
Wicmacterowrwbutawires i “oe ee ee oe Dia ere Wed. 0.9 c.m. 
OCLC KOTREUOUM LUC meses eh eS EN A Se 75° 
A 3 per cent variation from the above requirements is allowed. 
Thermometers should be thoroughly annealed and filled with 
carbon dioxide or nitrogen under pressure. The mercury column 
should rise from 15° to 95° in not more than five seconds, when 
plunged into boiling water. 
The thermometers are calibrated by setting up the entire apparatus 
(fig. 12) as though a distillation of tar were to be made. One hun- 
dred cubic centimeters of material of known boiling point is placed 
in the flask, which is then heated until the contents distil over at a 
uniform rate and the thermometer indicates a constant temperature, 
which is noted. By using three different materials of widely vary-- 
ing boiling point, three calibrations on the thermometer scale are 
obtained from which other intermediate points may be plotted. 
The correct fractionating points for the calibrated thermometer are 
then ascertained. | 
For calibrating thermometers in the laboratories of the Office of 
Public Roads and Rural Engineering the fractionating points are ob- 
tained from the distillation of distilled water (boiling point 100° C.), 
chemically pure naphthalene (boiling point 218.2° C.), and chemi- 
cally pure benzophenone (boiling point 305° C.). The boiling point, 
of course, varies with the barometric pressure, but if the thermome- 
ters are calibrated at a time when the barometer indicates about the 
