100 
BULLETIN 1036, U. S. DEPARTMENT OF AGRICULTURE. 
water. The usual precautions of igniting the pan before use, and avoiding the enclos- 
ure of air or water in the sample, should be observed. 
Note. — The method for liquid fractions is usually applicable to the fractions 235° 
to 315° C. and the method for solid and semisolid fractions to the fraction 315° to 
355° C. 
FLOAT TEST. 
The float test is used for the detection and limitation of the amount 
of tar in creosote or creosote-tar solutions. It has been adopted by 
the American Wood Preservers' Association, the American Railway 
Engineering Association, and the American Society for Testing 
Materials. The apparatus consists of an asphalt viscosimeter made 
of a float or saucer of aluminum and two conical brass collars. In 
making the test a brass collar is filled with the residue left after dis- 
tillation of the oil up to 355° C. It is then immersed in ice water for 
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Fig. 48.— Apparatus used in float test. 
a time sufficient to chill it thoroughly, after which it is fitted into the 
saucer and floated on water that is heated to the temperature of the 
test. The time in seconds, taken from the time the saucer is placed 
in the warm water to the time when it breaks through the plug of 
tar is ameasure of the viscosity of the residue at the selected tempera- 
ture and hence a measure of the amount of pitch or tar contained in 
the sample under test. This test can not be relied upon absolutely 
because of the variability in the amount of residue above 355° C. 
The chances are, however, that some other test, such as the free- 
carbon test, or the coke-residue test, or the test of the specific gravity 
of the fractions, would eliminate such oils, although in many cases 
45 per cent or more of tar may be accepted under a specification per- 
mitting only 35 per cent. 
The method of conducting the float test recommended by the three 
societies is as follows : 
Float or saucer. — The float or saucer shall be made of aluminum, and shall be of the 
form and dimensions shown in figure 48. 
