10 



BULLETIN 314, U. S, DEPARTMENT OF AGRICULTURE. 



this bath for at least 15 minutes. Meanwhile the other cup is filled 

 about three-fourths full of water and placed on the tripod, and the 

 water is heated to any desired temperature at which the test is to 

 be made. This temperature should be accurately maintained, and 

 should at no time throughout the entire test be allowed to vary 

 more than one-half a degree centigrade from, the temperature selected . 

 After the material to be tested has been kept in the ice water for at 

 least 15 minutes, the collar with its contents is removed from the 

 plate and screwed into the aluminum float, which is then immediately 

 floated in the warmed bath. As the plug of bituminous material 



Fig. 5.— New York testing laboratory float apparatus. 



becomes warm and fluid, it is gradually forced upward and out of the 

 collar, until water gains entrance to the saucer and causes it to sink. 

 The time in seconds between placing the apparatus on the water 

 and when the water breaks through the bitumen is determined by 

 means of a stop watch and is taken as a measure of the consistency 

 of the material under examination. 



USE OF THE FLOAT TEST. 



This test is always made on viscous and semisolid refined tars, 

 and often on the viscous and semisolid petroleum and asphalt prod- 

 ucts, although, when the penetration test can be employed on the 

 two latter classes of material, the float test is not always considered 

 necessary. For the more fluid products the test is made at 32° C. 

 and for the semisolid materials, at 50° C. When the material under 

 examination is quite hard, the test may be run at 100° C. 



