166 METHODS OF ANALYSIS. 



(d) EXAMINATION. 



Mount a small quantity of the ground sample in water and examine under 

 the compound microscope with both ordinary and polarized light. This gives 

 a general insight into the nature of the material and serves for the detection 

 and identification of starch granules and various tissues. 



Draw a small drop of iodin solution into the same preparation by means of 

 a piece of filter paper placed on the opposite edge of the cover glass and 

 examine. Starch granules will be colored blue or blue-black, cellulose yellow, 

 and proteids either brown or yellow. 



In the manner described draw a little potassium hydroxid solution under 

 the cover glass and examine once again. This treatment gelatinizes the starch 

 granules, dissolves the proteids, saponifies the fats, and in other ways clears 

 the preparation. It also imparts to tannins a reddish color. 



If treatment with potash does not clear the tissues satisfactorily, treat a 

 fresh portion for some hours with chloral hydrate solution. 



Examine also the crude fiber obtained in the chemical analysis, as in this 

 material the stone cells and other tissues are beautifully distinct. 



To isolate stone cells, bast fibers, and other thick-walled cells macerate a 

 portion of the sample in Schultze's liquid, using such proportion of potassium 

 chlorate and 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) granules, 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 perceptibly 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 

 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 carbonate, treat with acetic acid, which does not affect the former, 

 but dissolves the latter with effervescence. Both are soluble in hydrochloric 

 acid. 



Other special 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 histological elements, which can be 

 learned only by experience. 



Q Winton, Conn. Agr. Exper. Stat. Kept., 1896, p. 34. 



