EXAMINATION OF BITUMINOUS RCAD MATERIALS. 9 
end 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: 
Specific viscos-_ seconds for passage of given volume at a° ©. 
ity at a°C. seconds for passage of same volume of water at 25° ©. 
USE OF VISCOSITY DETERMINATION. 
For all thin fiuid bitumimous road materials the specific viscosity 
is determined at 25° C. with 50 or 100 cubic centimeters. Viscous 
fluid products are run at 40° C. or 50° C. with 50 cubic centimeters 
and very viscous products at 100° C. or over with 50 cubic centimeters. 
This test is not always made on the materials above mentioned, but 
is a useful one when they are required to have a given degree of 
fluidity at a given temperature. 
FLOAT TEST. 
EQUIPMENT, 
1 aluminum float or saucer. (Fig. 5-a.) 
2 conical brass collars. (Fig. 5-b.) 
2 1-quart tin cups, seamless. 
2 chemical thermometers reading from — 10° G. to 110° C. 
1 iron tripod. 
1 Bunsen burner and rubber tubing. 
i burette clamp and support. 
1 jarge metal kitchen spoon. 
1 steel spatula or kitchen knife. 
1 brass plate 5 by 8 centimeters. 
1 stop watch. . 
METHOD. 
The float pee consists of ino parts, an alumimum float or 
saucer (fig. 5-a@) and a conical brass collar (fig. 5-b). The two parts 
are made separately, so that one float may be used with a number of 
brass collars. 
In making the test the brass collar is. placed with the small end 
down on the brass plate, which has been previously amalgamated 
with mercury by first rubbing it with a dilute solution of mercuric 
chloride or nitrate and then with mercury. A small quantity of 
the material to be tested is heated im the metal spoon until quite 
fluid, with care that it suffers no appreciable loss by volatilization 
and that it is kept free from air bubbles. It is then poured into the 
collar in a thin stream until slightly more than level with the top. 
The surplus may be removed, after the material has cooled to room 
temperature, by means of a spatula or steel knife which has been 
slightly heated. The collar and plate are then placed in one of 
the tin cups containing ice water maintained at 5° C., and left in 
8916°—Bull. 314—15——2 
