Ol'KltA Y

• to

nth
the
cm-
» or

ict
ffi-
ild

sat

he

Effect of Quartering.—The reason for dividing into quartern
after each mixing and for selecting opposite quarters will bo
understood from the following: Close examination of the pilo
of unmixed material will reveal the fact that, even after the* most
thorough and careful mixing, it is not entirely homogeneous
Around the circumference of the base the particles are coarser
and they may be gathered toward one side. Around the apex of
the conical pile there is a
collection of coarser parti-
cles. If we simply dig in
at random for the portion
to be removed the lack of
homogeneity will alter the
character of this portion.

Figure 3 shows how the
opposite quarters, no mat-
ter in what direction the
cuts be made, will obtain
the average of a non-
homogeneous pile, while a
cut into halves will do so
only in case* the out is made
in the direction aft. In
these diagrams the condi-
tions are purposely exag-
gerated.

The Riffle.......-Various

r . • i A- !''««*• '*' 'H"1 rifflr,

forms of senn-automatic

sampling devices arc4 in use, designed to carry out the mixing
and dividing process without laborious hand work. Tho riflli*
is one of these. AH shown in Fig. 4 this consists of a hopper,
at the bottom of which are placed several narrow o.hutos, HO
arranged as to transfer alternating adjacent portions of fh<»
crushed material to opposite Hides and into separate* pans (not
shown in the illustration). This will have approximately flu*
same effect as would cutting the pile of material into vorfi<"»l,
narrow .sections, alternate portions being united so that f ho pilo
is finally halved. Tho riffle may bo made of any convenient si/o,
to handle large* or small samples.