The Wonder Island Boys | Page 9

"Are the alloys of all metals harder than the metals of which they are

made?"
"This seems to be a universal law in the compounding of metals. Very
few metals are used alone in the various arts and manufactures. For
every purpose some combination has been found which makes the
product better. Even coins are so alloyed. Silver and gold in the form of
money would be entirely too soft, unless alloyed with some hardening
metal. Some substances, like arsenic, antimony and bismuth, are too
brittle to be used alone. The only metals which can be used alone are
aluminum, zinc, iron, tin, copper, lead, mercury, silver, gold and
platinum."
"What is bronze, of which all the ancient guns were made?"
"That is a combination of copper and tin. This product was known fully
seven hundred years before the Christian era, and 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making of guns until superseded by the various steel alloys of our day."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
down on the inner course. It will be understood that the sides and
bottom thus formed were to be overlaid with thin boards running fore
and aft, as in Fig. 2, as they had no means for matching the boards and
thus putting them together tightly.
The sides were two and a half feet high. Six and a half feet from the
forward end was a cross beam (C), into which the mast was to be
stepped. At the stern the bottom was sloping upwardly at an angle and
brackets (D) were extended back and joined at their rear ends, to which
the lower end of the rudder post was attached.

Amidships a keel (E) was formed, projecting down from the bottom,
this keel being, at its widest part, two feet, and tapering down to merge
with the bottom, fore and aft. The cross section (Fig. 4) shows how
well he had formed the vessel, proportionally.
[Illustration: Fig. 4. Cross Section.]
In addition to the cross seats, similar arrangements for comfort were
made along the sides, and beneath the side seats were spaces in which
their supplies were to be placed. The space forward of the mast was
entirely closed over with a roof which sloped in both directions, and
here provision was made for two berths. This would also afford them
protection and