Source : Webster's Revised Unabridged Dictionary (1913)

   {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.

Impression \Im*pres"sion\, n. [F. impression, L. impressio.]
   1. The act of impressing, or the state of being impressed;
      the communication of a stamp, mold, style, or character,
      by external force or by influence.

   2. That which is impressed; stamp; mark; indentation;
      sensible result of an influence exerted from without.

            The stamp and clear impression of good sense.
                                                  --Cowper.

            To shelter us from impressions of weather, we must
            spin, we must weave, we must build.   --Barrow.

   3. That which impresses, or exercises an effect, action, or
      agency; appearance; phenomenon. [Obs.]

            Portentous blaze of comets and impressions in the
            air.                                  --Milton.

            A fiery impression falling from out of Heaven.
                                                  --Holland.

   4. Influence or effect on the senses or the intellect hence,
      interest, concern. --Reid.

            His words impression left.            --Milton.

            Such terrible impression made the dream. --Shak.

            I have a father's dear impression, And wish, before
            I fall into my grave, That I might see her married.
                                                  --Ford.

   5. An indistinct notion, remembrance, or belief.

   6. Impressiveness; emphasis of delivery.

            Which must be read with an impression. --Milton.

   7. (Print.) The pressure of the type on the paper, or the
      result of such pressure, as regards its appearance; as, a
      heavy impression; a clear, or a poor, impression; also, a
      single copy as the result of printing, or the whole
      edition printed at a given time.

            Ten impressions which his books have had. --Dryden.

   8. In painting, the first coat of color, as the priming in
      house painting and the like. [R.]

   9. (Engraving) A print on paper from a wood block, metal
      plate, or the like.

   {Proof impression}, one of the early impressions taken from
      an engraving, before the plate or block is worn.