A practical mechanic communicates to the Scientific American the
following: In hardening and tempering a cold chisel care should be taken
to have a gradual shading of temper. If there is a distinct boundary
line of temper color between the hard cutting edge and softer shank
portion, it will be very apt to break at or near that line. The cutting
edge portion of the chisel should be supported by a backing of steel
gradually diminishing in hardness; and so with all metal cutting tools
that are subjected to heavy strain. Not every workman becomes uniformly
successful in this direction, for, in addition to dexterity, it requires
a nice perception of degree of heat and of color in order to obtain the
best result.

* * * * *

MR. A. A. KNUDSON, of Brooklyn, N. Y., has lately perfected and patented
a system of protecting oil tanks from lightning, which is approved by
several prominent electricians. The invention includes a device for
distributing a spray of water over the top of the tank for condensing
the rising vapor and cooling the tank; a system of lightning conductors
connected with a gutter surrounding the tank, and a hollow earth
terminal connected with the gutter by a pipe, and designed to moisten
the earth, and at the same time prevent the earth around the terminal
from becoming saturated with oil.

* * * * *

A correspondant of the _Christian Union_, writing from Constantinople,
says that Abd ul-Hamid, the Sultan of Turkey, reads the Scientific
American, the engravings in which seem to specially interest him. The
writer adds that whatever in literature the Sultan may chance to hear of
which he thinks may interest him, he has translated into Turkish.

* * * * *

AMATEUR MECHANICS.

A SIMPLE SINGLE-ACTING STEAM ENGINE.

The great bugbear staring the amateur mechanic in the face when he
contemplates making a small steam engine is the matter of boring the
cylinder. To bore an iron cylinder on a foot lathe is difficult even
when the lathe is provided with automatic feed gear, and it is almost
impossible with the ordinary light lathe possessed by most amateurs. To
bore a brass cylinder is easier, but even this is difficult, and the
cylinder, when done, is unsatisfactory on account of the difficulty of
adapting a durable piston to it.

The engravings show a simple steam engine, which requires no difficult