the hole requires the greatest amount of work. After this
has been done it is a simple matter to cut the V-shaped grooves. The
reamer should be applied at the center, that is, the grooves should be
cut on the axis or full diameter of the hole. The gauge of the reamer
should be at least 11/2 diameters. Great care should be taken that the
reamer does not twist, as the break may be thereby deflected; and the
reaming must be done also to the full depth of the hole.

The hole is now ready for charging. The powder should be a low
explosive, like black or Judson powder or other explosives which act
slowly. No definite rule can be laid down as to the amount of powder
to be used, but it should be as small as possible. Very little powder
is required in most rocks. Hard and fine grained stone requires less
powder than soft stone. Mr. Knox tells of a case which came under his
observation, where a block of granite "more than 400 tons weight,
split clear in two with 13 oz. of FF powder." He compares this with a
block of sandstone of less than 100 tons weight "barely started with
21/2 lb. of the same grade of powder, and requiring a second shot to
remove it."

It is obvious that enough powder must be inserted in the hole to
produce a force sufficient to move the entire mass of rock on its bed.
In some kinds of stone, notably sandstone, the material is so soft
that it will break when acted upon by the force necessary to shear the
block. In cases of this kind a number of holes should be drilled and
fired simultaneously by the electric battery. In such work it is usual
to put in the holes only 4 or 5 ft. apart. The powder must, of course,
be provided with a fuse or preferably a fulminating cap. It is well to
insert the cap at or near the bottom of the cartridge, as shown in
Figs. 8 and 9.

After the charge the usual thing to do is to insert tamping. In the
improved form of hole the tamping should not he put directly upon the
powder, but an air space should be left, as shown at B, Fig. 8. The
best way to tamp, leaving an air space, is first to insert a wad,
which may be of oakum, hay, grass, paper or other similar material.
The tamping should be placed from 6 to 12 in. below the mouth of the
hole. In some kinds of stone a less distance will suffice, and as much
air space as practicable should intervene between the explosive and
the tamping. If several holes are used on a line they should be
connected in series and blasted by electricit