308 
ELEMENTARY CHEMICAL MICROSCOPY 
h. Prepare a film of KCl. Draw across it an alcoholic solution of picric acid 
C6H2(N02)30H. Potassium picrate C6H2(N02)30K is obtained in long acicular 
prisms of the orthorhombic system. Try in like manner, Na, NH4 and Cs chlorides. 
Try with Na2C03. 
VIII. The reagent is incorporated into a fiber of silk, cotton, 
wool, or in a filament of guncotton 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.^ 
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; v/ool 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., 361 (1907), 426. 
* Donau, Monats., 26 (1904), 545; Ann., 361 (1907), 432. 
