Strain in a Rope over a Pulley, and Refining Gunpowder
Why the mover's cord tires more than the weight's cord, and how to grind and store niter, sulfur and charcoal
Under the repeated heading 'Cord', the folio analyses the unequal fatigue in the two lengths of a rope running over a pulley (illustrated by a small pendulum-and-pulley figure at the top right lettered a, c b). Leonardo argues that the length between the weight and the pulley never feels more force than the weight itself, while the length between the pulley and the mover carries the mover's greater power plus the friction of the pulley's axle; the mover's cord therefore always tires more, even when air resistance drags on a fast-descending load. A final paragraph returns to gunpowder, advising that niter, sulfur and charcoal be more finely refined for smaller pieces, kept separate until needed, and, if stored ready-made, kneaded with strong vinegar into loaves and dried.
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The mover's cord tires more than the weight's cord
The length of cord between weight and pulley never feels any force greater than the weight itself, whereas the length descending from the pulley to the mover carries the mover's power, which exceeds the load and must also overcome the friction of the pulley's axle. Hence the mover's side always suffers greater strain.
Air resistance on a fast-descending load
When the mover greatly outweighs its load, its descent becomes very fast and the load follows at the same speed; the air condensing before the moving body adds resistance to the cord. Even so, because the load is always less powerful than the mover, the load's cord suffers less than the mover's.
Refining and storing niter, sulfur and charcoal
The three ingredients should be more finely refined and the charcoal fresher for smaller guns; sulfur citrine and live, not black; all ground to minute particles and mixed. For munitions the substances are best kept separate until needed, since saltpeter and sulfur together corrode one another; charcoal absorbs damaging moisture. Ready-made powder should be kneaded with strong clear vinegar into 6-8 pound loaves and dried.