16 BULLETIN" 87, U. S. DEPARTMENT OF AGRICULTURE. 
torn of the flunie. In consequence the water is forced over the sides, 
and usually throws the material out of the flunie, especially if the 
curve is on an abrupt descent, or else the constantly increasing 
weight of the jam breaks the legs of the trestle, if there be one at this 
point, or perhaps causes the whole framework to collapse. It is then 
often a matter of considerable loss of time and expense before the 
flume is repaired and again ready for operation. The degree of 
curvature should be kept as low as practicable, and should rarely 
be permitted to exceed 20°. 
The length of material to be transported is an important factor in 
deciding the degree of curve that can be used, since very long material 
can not be successfully transported in a flume having a very abrupt 
curve. The curve would have to be sufficiently open to allow the 
chord of curve to be represented by the length of the longest material 
desired to be handled, with a small allowance for clearance. No 
curves should be used in construction that will cause the material 
to "bind." The longer the material the less abrupt curvature is 
permissible, and vice versa. The bracing of a flume on the outside 
of the curve necessarily should be more rigid and stronger than on 
the inside, since the greater pressure "thrust" or "throw" of the 
water and material being shipped is toward the outside of the curve. 
Very abrupt curves require increased bracing and the placing of the 
arms and brackets at shorter intervals, in order to hold the flume 
in its proper position. 
Shorter "boxes" and closer spacing of "bents, " "arms, " and "braces " 
on curves. — Where the topographic conditions in a locality are such 
that it becomes absolutely necessary to have abrupt curves in a 
flume, it is advisable to reduce the length of the boxes and correspond- 
ingly shorten the distance that the "bents," "arms," and "braces" 
are placed apart, for the twofold purpose of evening up or reducing 
the sharpness of the angles in the joining of the boxes on the curve, 
and also to give more stability and strength to the flume at the points 
where there will be the greatest strain upon it. It will be apparent 
that long boxes in a flume at a point where there was an abrupt 
degree of curvature would necessitate sharper changes in direction 
than would shorter boxes, thus producing something in the nature 
of square corners. These corners, particularly if there were a rapid 
descent in the flume line at such curve, would have an effect some- 
thing in the nature of a dam or stoppage in the flume, and as a result 
cause the water to slop over or run out over the sides. In addition, 
all material coming down the flume, as a result of the quick change 
in the direction of its course, would "strike" sharply against the 
outside "corner, " and the continual pounding of the material against 
the side of the flume would be very likely to jar and eventually 
loosen up the joints at this point, throw the flume out of alignment, 
