You may know when the fire is good and fit for your purpose by a
clear flame, and if you see the tips of the flames dull and ending
in much smoke do not trust it, and particularly when the flux metal
is almost fluid.

OF ALLOYING THE METAL.

Metal for guns must invariably be made with 6 or even 8 per cent,
that is 6 of tin to one hundred of copper, for the less you put in,
the stronger will the gun be.

WHEN THE TIN SHOULD BE ADDED TO THE COPPER.

The tin should be put in with the copper when the copper is reduced
to a fluid.

HOW TO HASTEN THE MELTING.

You can hasten the melting when 2/3ds of the copper is fluid; you
can then, with a stick of chestnut-wood, repeatedly stir what of
copper remains entire amidst what is melted.

_Introductory Observations on the Architectural Designs (XII), and
Writings on Architecture (XIII)._

_Until now very little has been known regarding Leonardo's labours
in the domain of Architecture. No building is known to have been
planned and executed by him, though by some contemporary writers
incidental allusion is made to his occupying himself with
architecture, and his famous letter to Lodovico il Moro,--which has