EXAMINATION OF BITUMINOUS ROAD MATEBIALS. 9 



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: 



Specific viscos-_ seconds for passage of given volume at a° C. 

 ity at a° 0. seconds for passage of same volume of water at 25° (J. 



USE OF VISCOSITY DETERMINATION. 



For all thin fluid bituminous 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. 5-6.) 

 2 1-quart tin cups, seamless. 



2 chemical thermometers reading from — 10° C. to 110° C. 



1 iron tripod. 



1 Bunsen burner and rubber tubing. 



1 burette clamp and support. 



1 large metal kitchen spoon. 



1 steel spatula or kitchen knife. 



1 brass plate 5 by 8 centimeters. 



1 stop watch. 



METHOD. 



The float apparatus consists of two parts, an aluminum float or 

 saucer (fig. 5-a) and a conical brass collar (fig. 5-6). 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 lias 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 in 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 

 itly heated. The collar and plate are then placed in one of 

 the in) cups containing ice water maintained at 5° C, and left in 

 Hu\c, r - Bull. 314—15 2 



