458 ELEMENTARY CHEMICAL MICROSCOPY 



Straw. — (a) Cells like those (a) of esparto, but longer and ends somewhat 

 less tapering and blunter. 



(b) Large, coarse, roughly serrated cells. 



(c) Almost oval, thin, very transparent cells. No short comma-shaped hairs. 

 Large, irregular, many pitted cells also abound. 



Manila. — Resembles hemp but cells are more pointed and are somewhat 

 shorter and have thinner walls and a larger and more prominent central canal. 

 There are also curious thin, transparent cells approximately twice as long as broad 

 with rounded ends. The cells occur singly or in groups or masses. 



Differentiation of Paper Fibers by Iodine and Sulphuric Acid. 1 — Method of test- 

 ing described above must be closely followed and the strength of the two reagents 

 must closely approximate the concentrations given, otherwise the fibers will not 

 develop the color given below. 



i. With Iodine Reagent = Solution A. 



Brown Fibers = Cotton (rags); linen; bleached hemp. 

 Yellow Fibers = Mechanical wood; jute; straw. 

 Gray to Brown = Manila, Adansonia. 



Gray or almost uncolored = Esparto; bleached straw; bleached jute; chem- 

 ical wood. 



2. Solution A followed by Sulphuric acid (Solution B). 



Violet, Violet Red or Wine Red = Cotton; linen; bleached jute; esparto. 

 Blue or Blue-gray = Chemical wood; straw; esparto. 

 Golden Yellow or Dark Yellow = Mechanical wood; jute; manila. 

 Brown = (if over stained = cotton; linen; bleached jute). 



Differentiation of Paper Fibers by Herzberg's Stain. — This reagent is in some 

 respects superior to staining with iodine and sulphuric acid, provided care is taken 

 to properly prepare and to properly adjust the reagent. It is never safe to depend 

 upon a reagent which has not been tested out upon known materials and found 

 to yield with them the correct color reactions. 2 



1 The reagents as employed in this laboratory are made as follows: 



Solution A. 



Potassium Iodide 5 grams 



Distilled water ioo c.c. 



Iodine 2.85 grams 



Glycerine 5 c.c. 



Solution B. 



Sulphuric acid Sp. Gr. 1.45. 



2 Herzberg's Stain may be prepared as follows: 

 Solution A. 



Dissolve Zinc Chloride in water until a specific gravity of approximately 2.00 



is obtained. 

 Solution B. 



Water 50 c.c; Potassium Iodide 30 gms.; add Iodine until an excess remains 



undissolved after standing for several days. 

 For use decant 9 c.c. of Solution A and add 1 c.c. of Solution B. 



