What is "proof staff"

Proof \Proof\, a.

1. Used in proving or testing; as, a proof load, or proof charge.

2. Firm or successful in resisting; as, proof against harm; waterproof; bombproof.

   I . . . have found thee Proof against all temptation.
   --Milton.

   This was a good, stout proof article of faith.
   --Burke.

3. Being of a certain standard as to strength; -- said of alcoholic liquors.

   Proof charge (Firearms), a charge of powder and ball, greater than the service charge, fired in an arm, as a gun or cannon, to test its strength.

   Proof impression. See under Impression.

   Proof load (Engin.), the greatest load than can be applied to a piece, as a beam, column, etc., without straining the piece beyond the elastic limit.

   Proof sheet. See Proof, n., 5.

   Proof spirit (Chem.), a strong distilled liquor, or mixture of alcohol and water, containing not less than a standard amount of alcohol. In the United States ``proof spirit is defined by law to be that mixture of alcohol and water which contains one half of its volume of alcohol, the alcohol when at a temperature of 60[deg] Fahrenheit being of specific gravity 0.7939 referred to water at its maximum density as unity. Proof spirit has at 60[deg] Fahrenheit a specific gravity of 0.93353, 100 parts by volume of the same consisting of 50 parts of absolute alcohol and 53.71 parts of water,'' the apparent excess of water being due to contraction of the liquids on mixture. In England proof spirit is defined by Act 58, George III., to be such as shall at a temperature of 51[deg] Fahrenheit weigh exactly the 12/13 part of an equal measure of distilled water. This contains 49.3 per cent by weight, or 57.09 by volume, of alcohol. Stronger spirits, as those of about 60, 70, and 80 per cent of alcohol, are sometimes called second, third, and fourth proof spirits respectively.

   Proof staff, a straight-edge used by millers to test the flatness of a stone.

   Proof stick (Sugar Manuf.), a rod in the side of a vacuum pan, for testing the consistency of the sirup.

   Proof text, a passage of Scripture used to prove a doctrine.