Weighing lead against water: a specific-gravity experiment
Apparatus and procedure for finding how many measures of water equal a measure of lead
The page lays out an experiment to determine how many equal measures of water balance the weight of a given measure of lead, and how much water a submerged lead cylinder displaces above its level. A lead cylinder (labelled 'piombo') stands on a turned pedestal, while a wire-caged vessel — the 'bottino' whose armature of soldered iron wires wrapped on an ox-gut core is described at right — serves as the measuring apparatus. Leonardo tabulates variations in the thickness and length of lead, cage and tube to gauge the power of every 'water instrument', and closes with a wax-coating method for finding lead's true water-counterweight. The subject is hydrostatics and specific weight, applied to metals, stone, earth, wood and liquids.
On this page
How many measures of water equal the weight of lead
The instrument is meant to reveal how many times a pound of lead raises its own bulk in a sum of water, i.e. how much water a measure of lead pushes above its level. By repeatedly matching lead, cage and tube at equal, half and quarter thickness — lengthening what is lost in width — one can judge exactly the power of any water instrument.
Making the wire cage (bottino)
The measuring cage is built from iron wires forming an armature that surrounds it, cut at the point m n, then soldered and fastened to a thick ox gut in a columnar shape and fixed with varnish at whatever spacing seems best.
The wax-coat counterweight rule
To find how many measures of water a measure of lead needs as counterweight, a turned piece of lead an ounce thick is greased with soap, dipped five or six times in a wax bath to give it a firm coat, then withdrawn; water or wine is measured out until it balances the lead, always subtracting the weight of the wax.
