62 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



nitric acid and heating for such a time as secures the desired results. Powdered 

 charcoal and charred shells resist the bleaching action of potash, chloral hydrate, 

 and Schultze's liquid, the fragments after, as before the treatment, being black and 

 opaque. 



If it is desired to distinguish cellulose from infiltrated substances (lignin,' suberin, 

 etc.), add to a water mount freshly prepared chlorzinc iodin, which colors the 

 former blue and the latter yellow. 



As a test for proteids, cautiously warm, on a slide, with a drop of freshly prepared 

 Millon's reagent. The proteids are partially disorganized, taking on gradually a 

 brick-red color. If it is desirable to study the form of the aleurone (proteid) gran- 

 ules, which in some plants are quite as characteristic as starch granules, prepare a 

 mount in pure glycerin or oil. 



To distinguish fats, oils, essential oils, and resins from other cell contents, treat for 

 an hour with alkanna tincture diluted with an equal bulk of water, which imparts to 

 these substances a deep red color; or treat with ether, which dissolves them. Treat 

 also with alcohol, which dissolves the essential oils and resins but does not percep- 

 tibly affect the fats and oils. 



In testing for tannins and tissues impregnated with those substances, add ferric 

 acetate or chlorid solution. Both of these reagents give with tannins a green or 

 blue color, but the former acts more slowly and is to be preferred. 



Crystals of calcium oxalate are recognized by their characteristic forms and their 

 deportment with polarized light. To distinguish calcium oxalate from calcium car- 

 bonate, treat with acetic acid, which does not affect the former but dissolves the 

 latter with effervescence. Both are soluble in hvdrochloric acid. 



Other special reagents may be occasionally useful, but as a rule, reagents play 

 a subordinate part in the microscopic examination of spices, the chief factor being a 

 thorough understanding of the size, shape, color, and other characteristics of the 

 histologieal elements, which can be learned only by experience. 



XI. YINEGAR. 



By WM. FREAR, 

 Chemist of State Experiment Station, State College, Pa. 



Vinegars may be defective because of the poor quality of the liquids from which 

 they are prepared or because of incomplete fermentation; impure from the develop- 

 ment of abnormal fermentations, invasion of vinegar eels (Anguillnla oxophila), 

 moulds, or presence of foreign substances accidentally introduced, such as metallic 

 salts formed by the action of the acid upon metallic vessels, faucets, etc.; adulterated, 

 as by dilution, addition of mineral acids, pungent materials, coloring matters, etc. ; 

 misbranded, as when a pure vinegar of one sort is sold under the name of another. 

 It is needful that methods for the detection of all the foregoing classes of variations 

 shall be employed as occasion demands; that is, variation in normal constituents as 

 well as presence of foreign matters must be detected and often measured. 



1. PREPARATION OF SAMPLES. 



For microscopic examination, the original sample should be employed, but for 

 chemical analysis the vinegar should be filtered, if turbid from the presence of sus- 

 pended solids. Samples should be kept in glass bottles with ground-glass stoppers 

 and should be promptly analyzed to avoid fermentative changes, which progress 

 rapidly in the warm air of the laboratory. 



2. CALCULATION OF KESULTS. 



Express all results as per cent by weight. Owing to the slight departure of the 

 specific gravity of vinegars from that of water, no error of importance in most con- 



