60 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



18. DETERMINATION OF TANNIN EQUIVALENT BY THE LOWENTHAL-RICHARDSON 



METHOD. a 



(For cloves and allspice.) 



Extract 2 grams of material 20 hours with absolute ether. Boil the residue 2 

 hours with 300 cc of water, cool, make up to 500 cc and filter. Measure 25 cc of this 

 infusion into a flask of about 1,200-cc capacity, add 20 cc of indigo solution and 750 cc 

 of distilled water. Run in standard permanganate solution at the rate of one or two 

 drops a second, with constant shaking, until a bright golden yellow color appears. 



Determine in the same manner the number of cubic centimeters of permanganate 

 solution consumed by 20 cc of indigo solution alone and subtract from the number 

 consumed by the spice infusion and indigo solution together. 



Indigo solution must be made from sodium sulphindigotate of best quality (such 

 as is furnished by Gehe & Co., Dresden, or Grueber & Co., Leipzig), otherwise the 

 titration will not be sharp. Dissolve 6 grams of the salt in 500 cc of water, with the 

 aid of heat. Cool, mix with 50 cc of concentrated sulphuric acid, make up to 1 

 liter and filter. 



Prepare standard potassium permanganate solution by dissolving 1.333 grams of 

 the pure salt in 1,000 cc of water. Standardize by titration of 10-cc portions of 

 decinormal oxalic acid solution (6.3 grams of the pure crystallized acid in 1,000 cc), 

 which have been previously diluted to 500 cc, heated to 60 C. and mixed with 20 cc 

 of dilute sulphuric acid (1:3 by volume). Add the permanganate solution slowly, 

 with constant stirring, until a pink color appears. Ten cubic centimeters of decinor- 

 mal oxalic acid solution are equivalent to 0.06232 gram of quercitannic acid, or 

 0.008 gram of "oxygen absorbed." 



Ellis first recommended the determination of tannin as a means of detecting adul- 

 teration, but Richardson found that the abbreviated method here described is quite 

 as useful as the more tedious process for the actual determination of tannin. 



19. MICROSCOPICAL EXAMINATION. 



As already stated, the microscope is the most valuable means of detecting adulter- 

 ants of vegetable origin in spices, as it usually discloses the particular adulterant 

 present, even when in small amount. The analyst who undertakes this work should 

 have a general knowledge of vegetable histology and microscopic manipulation, and 

 should be thoroughly familiar with the microscopic appearance of the spices and the 

 spice adulterants. He should have at his command the standard works on these 

 subjects, and also a set of standard samples of all the materials likely to be encoun- 

 tered. The following works are especially recommended: 

 Moeller. Mikroskopie der Nahrungs- und Genussmittel aus dem Pflanzenreiche. 



Berlin, 1886. 



VogL Die wichtigsten vegetabilischen Nahrungs- und Genussmittel. Berlin, 1899. 

 Tschirch und Oesterle. Anatomischer Atlas der Pharmakognosie und Nahrungsmit- 



telkunde. Leipzig, 1900. 



Only a few general hints are here given: 



(a) APPARATUS. 



Dissecting microscope or hand lens. 



Compound microscope provided with f and J-inch objective, 1 and 2-inch oculars, 

 double nosepiece, eyepiece micrometer, and polarizing apparatus. 

 A series of sieves with meshes ranging from 0.2 to 2 mm. 

 Slides, cover glasses, needles, scalpels, forceps, etc. 



Allen. Commercial Organic Analysis, 1889, Vol. Ill, Part I, p. 109. U. S. Dept. of Agr., Div. of 

 Chem., Bui. 13, Part 2, p. 167. 



