was used in the making
of guns until superseded by the various steel alloys of our day."

"In what proportions are copper and tin united to make bronze?"

"The proportions vary greatly. Ancient Celtic bronze had 12 parts tin
and 88 of copper; Egyptian, 22 tin, 78 copper; Chinese, 20 tin, 80
copper; Roman, 15 tin, 85 copper; and in many specimens lead and zinc
were also used. Tin has a capacity to harden almost any metal."

"What is the best metal to harden steel?"

"Manganese, of which you will remember we have some samples; it is the
most serviceable, as we have neither nickel nor chromium."

"What amount of that metal should we use to get the best results?"

"About 14 per cent. of manganese has been found the best for such
purposes as would be required in gun barrels. There is a curious thing
which has been discovered in uniting manganese with steel. It becomes
fairly tough if 1 per cent. is used with the steel; if the quantity
added is between 1-1/4 and 3-1/2 the strength and ductility decrease;
but above that, up to 5 per cent., the steel becomes brittle; above
6-1/2 per cent. it again returns to ductility and toughness and its
maximum strength is found at 14 per cent."

During the evenings all took a hand at cutting out the stocks for the
guns, and the plans upon which they were constructed will be fully
explained and illustrated in the order of the work done.

Meanwhile it must not be supposed that work on the new boat had ceased.
Harry's plan, when fully worked out, provided for one twenty feet long
and six and a half feet wide amidships.

The drawing (Fig. 2) shows the construction of the hull. As they had no
means for doing any fancy bending of the boards, the bottom was made
flat, and the sides sloping. The bottom and the sides were made in the
following manner: Two stringers (A, A) were first constructed, which
were made up of thin pieces nailed together, so they could be bent in
the proper shape for the bottom boards, which were laid crosswise and
nailed to these stringers.

[Illustration: _Fig 2. TOP VIEW OF BOAT_]

[Illustration: _Fig 3. SIDE VIEW_]

For the upper edges of the sides, called the gunwale (B, B), similar
stringers were provided, but they extended farther fore and aft, and
amidships were fully six and a half feet apart, whereas the lower
stringers amidships were four and a half feet apart. This arrangement,
therefore, provided for sloping sides, and the side pieces ran up and
do