38 
BULLETIN 1373, U. S. DEPARTMENT OE AGRICULTURE 
The equipment (fig. 30) consisted mainly of a cast-iron exhaust 
fan with, a 9-inch inlet, driven by an electric motor and operated at 
about 2,700 revolutions per minute. A grain trap, with a cross- 
sectional area ten times the area of the 9-inch duct, was installed in 
the pipe line to the fan inlet. , To measure the velocities at which 
the various grains were lifted, a hood, 12 inches in diameter, was 
placed at the end of a 9-inch pipe leading to the grain trap. The 
grain was placed upon a tightly drawn No. 14 mesh copper screen 
9 inches from the open bottom of the hood. A thin celluloid guide, 
6 inches in diameter and* 2 inches high, was fastened to the screen 
to keep the grain on the screen where the air velocity was fairly 
uniform and where the velocity readings were to be taken by a 
pitot tube. The guide was divided into four sections to keep the 
grain evenly distributed over the screen. The pitot tube readings 
were taken in the center of these four sections, about 2J^ inches 
above the screen. 
Exhaust Fan 
Speed -270 rp.m ~^-^ /g .- 
Fig. 30.— Equipment used for air-velocity experiments 
Preliminary experiments showed that the air velocity was prac- 
tically uniform at all points inside the guide. The total and static 
pressure readings of the pitot tube were taken with a differential 
manometer, graduated for readings in thousandths of an inch. Oil 
containing a red dye and having a specific gravity of 0.83 was used 
instead of water in order to make the manometer more sensitive 
and more easily read. 
One hundred kernels of grain (corn, wheat, or oats) were placed 
inside the celluloid guide. In the first run the air velocity was 
regulated by a butterfly valve and slide door near the inlet of the 
fan, so that all the grain in the guide was just lifted from the screen. 
Pitot tube readings were taken to determine the velocity.* In the 
next run the grain was replaced in the guide as before and the air 
