258 METHODS OF ANALYSIS 



acidity as directed in 17, and determine total tartaric acid in a 100 cc. aliquot as 

 directed under XVI, 29, except that 20 cc. of alcohol are used in the precipitation 

 instead of 15 cc. 



FREE MINERAL ACIDS. 



26 Logivood Method'^. — Tentative. 



Prepare an extract of logwood as follows: Pour 100 cc. of boiling water upon 2 

 grams of fresh logwood chips, allow the infusion to stand for a few hours and filter. 

 Place drops of the liquid on a porcelain surface and dry on a water bath. Add to 

 one of the spots a drop of the vinegar to be tested (after concentration if desirable) 

 and evaporate to dryness. A yellow tint remains if free mineral acids are absent, 

 a red tint if they are present. 



27 Methyl Violet Method. — Tentative. 



Add 5-10 cc. of water to 5 cc. of vinegar and, after mixing well, add 4 or 5 drops 

 of methyl violet solution (1 part of methyl violet 2B in 10,000 parts of water). A 

 blue or green coloration indicates the presence of a free mineral acid. 



28 Quantitative Method. (Hehner Method) — Tentative. 



To a measured amount of the sample add a measured excess of standard alkali, 

 evaporate to dryness, incinerate and titrate the ash with standard acid, using 

 methyl orange as an indicator. The difference between the number of cc. of alkali 

 first added and the number of cc. of acid needed to titrate the ash represents the free 

 mineral acid present. 



29 METALS.— TENTATIVE. 

 Proceed as directed under XII. 



30 Qualitative Test. — Tentative. 



Evaporate 100 cc. of the vinegar to a volume of about 15 cc. Add slowly and 

 with constant stirring 200 cc. of 95% alcohol by volume and allow to stand over- 

 night. The precipitate formed should be tested for dextrin by the optical rotation 

 and color reaction with iodin. 



SPICES AND ADDED PUNGENT MATERIALS. 



31 Qualitative Test. — Tentative. 



Neutralize exactly a portion of the vinegar and test by taste and smell. Agitate 

 the liquid with ether in a separatory funnel, remove and evaporate the ethereal 

 layer, and note the odor and taste of the residue. 



32 COLORING MATTERS.— TENTATIVE. 

 Proceed as directed under XI. • 



33 PRESERVATIVES.— TENTATIVE, 

 Proceed as directed under X. 



BIBLIOGRAPHY. 



1 Z. Nahr. Genussm., 1911, 21: 1; 22: 88. 



2 Allen. Commercial Organic Analysis. 4th ed., 1909-14, 1: 503. 



