XIX. VINEGARS. 



(Unless otherwise noted, express results as grams per 100 cc.) 



1 PHYSICAL EXAMINATION.— TENTATIVE. 

 Note the appearance, color, odor and taste. 



2 PREPARATION OF SAMPLE.-TENTATIVE. 



If the sample is turbid, filter before proceeding with the analysis. 



3 SPECIFIC GRAVITY.— TENTATIVE. 

 Determine the specific gravity at '-^^ by means of a pycnometer. 



4 ALCOHOL.-TENTATIVE. 



Measure 100 cc. of the sample into a roimd-bottomed, distillation flask. Make 

 faintly alkaline with saturated sodium hydroxid solution, add a small piece of 

 paraflBn, distil almost 50 cc, make up to 50 cc. at the temperature of the sample 

 and determine the specific gravity at -ji— ' by means of a pycnometer. Obtain from 

 XVI, 5, the per cent by volume, or grams per 100 cc, noting that the alcoholic 

 strength of the distillate is twice that of the original vinegar. 



GLYCEROL.— TENTATIVE. 



5 REAGENTS. 



(a) Strong -potassium dichromale solution. — Dissolve 74.56 grams of dry, recrystal- 

 lized potassium dichromate in water, add 150 cc. of concentrated sulphuric acid, 

 cool and make up to 1 liter at 20°C. One cc. of this solution is equivalent to 0.01 

 gram of glycerol. The high coefficient of expansion of this strong solution necessi- 

 tates its preparation at exactly 20°C. and the measurement of any definite volume 

 at the same temperature. If desired, the measurements may be made at room 

 temperature by means of a weighing burette, the volume used in this case being 

 ascertained by dividing the weight of the solution used by its specific gravity at 

 20 "C. 



4° 



(b) Dilute potassium dichromate solution. — Measure 25 cc. of the strong potas- 

 sium dichromate solution at exactly 20°C. into a 500 cc volumetric flask, dilute with 

 water and make up to the mark at room temperature. Twenty cc. of this solution 

 are equivalent to 1 cc. of (a). 



(C) Ferrous ammonium sulphate solution. — Dissolve 30 grams of crystallized fer- 

 rous ammonium sulphate in water, add 50 cc. of concentrated sulphuric acid, cool 

 and dilute at room temperature. One cc. of this solution is approximately equiva- 

 lent to 1 cc of (b). Its value changes slightly from day to day and it must be 

 standardized against (b) whenever used. 



(d) Potassiiwi ferricijanid indicator. — Dissolve 1 gram of crystallized potassium 

 ferricyanid in 50 cc. of water. This solution must be freshly prepared. 



(e) Milk of lime. — Introduce 150 grams of calcium oxid, selected from clean, hard 

 lumps, prepared preferably from marble, into a largo porcelain or iron dish, slake 

 with water, cool and add suflicient water to make 1 liter. 



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