All of the instruments employed give accurate results only at the "normal temperature" for which it is made. As, however, in practice, the experiment cannot be conveniently performed at any "fixed" temperature, but only at that of the atmosphere, it is obvious that certain corrections are constantly required in order to obtain results of any value. Perfect accuracy requires that tables for every variation of the thermometer, founded on actual experiments, should accompany each instrument; as, without them, tedious and difficult calculations are necessary, which, in the hurry of laboratory work, or by persons inexpert at figures, are 'not easily performed. The United States' Custom House Scale with thermometer contains conveniently a table for corrections, and we advise the carbonator to employ this instrument for his service. Other Tralle's alcoholometers, with thermometer and correction table, can be had from any supply house or wholesale druggist and in nearly all countries. For rough purposes, in the absence of tables, the following calculations of Gay-Lussac may be found useful, which show that, for commercial spirits, at ordinary temperature, a variation of By Volume.

5° Fahr. is equal to (about) 1.00% of Alcohol; or (about) 1.794% of Proof Spirit. 1° " " " 0.20% " " 0.359%

5°Cels. " " 1.80% " " 3.229%

1° " " " 0.36% " " 0.646%

By Weight.

5° Fahr. is equal to (about) 0.80% of Alcohol; or (about) 1.62% of Proof Spirit 1° " " " 0.15% " " 0.32%

5° Cels. " " 1.43% " " 0.29%

1° " " " 0.28% " " 0.58%