308 ELEMENTARY CHEMICAL MICROSCOPY 



b. Prepare » film of KC1. Draw across it an alcoholic solution of picric acid 

 C6H 2 (N0 2 ) 3 OH. Potassium picrate C6H 2 (N0 2 ) 3 OK is obtained in long acicular 

 prisms of the orthorhombic system. Try in like manner, Na, NFL and Cs chlorides. 

 Try with Na 2 C0 3 . 



VIII. The reagent is incorporated into a fiber of silk, cotton, 

 wool, or in a filament of guncotlon and the prepared fiber dipped 

 into the drop of solution to be tested. 



The development of the methods for testing by means of 

 textile fibers into which are incorporated the reagents to be 

 employed, is due to Emich * and to Donau. 2 



That variety of fiber is chosen which has the highest adsorptive 

 power for the specific reagent to be used, as, for example, silk for 

 adsorbing litmus; viscose-silk for turmeric; silk or cotton for 

 gold; wool for adsorbing zinc sulphide, etc. 



Two methods of applying the reagent fiber to the test drop are 

 in vogue; one consists in laying the fiber across the drop of solu- 

 tion so that about two-thirds of its length will be outside the 

 drop. The liquid is drawn by the capillarity of the fiber so that 

 it gradually flows over its whole length. The second method 

 consists in rolling a bit of beeswax between the fingers until a 

 tiny slender cone is obtained about 10 millimeters long by 2 or 3 

 millimeters in diameter. One end of the reagent fiber is attached 

 to the apex of the wax cone and the base of the cone is gently 

 pressed against an object slide. A very minute rounded drop 

 of the solution to be tested is placed upon the slide about 5 milli- 

 meters away from the base of the cone; the cone is then bent 

 over until the free end of the fiber dips into the liquid. The 

 preparation is next placed upon the stage of the microscope and 

 the instrument focused upon the fiber just above the drop. 

 Through capillarity the liquid is drawn upon the fiber and the 

 reaction resulting is easily recognized. 



1 Emich, Monats., 22 (1901), 670; 23 (1902), 76; Ann., 351 (1907), 426. 



2 Donau, Monats., 25 (1904), 545; Ann., 351 (1907), 432. 



