THE METHODS OF MICROCHEMICAL QUALITATIVE ANALYSIS 271 



cyanate; as soon as the precipitate has dissolved add a very slight 

 excess of the ammonium salt. Too much ammonium sulpho- 

 cyanate decreases the sensitiveness of the reagent. 



Litmus-Silk-Fibers. 1 Boil a little raw silk with water, 

 decant and wash. Pour over the silk fibers a solution of pure 

 litmus. 2 Evaporate on the water bath to small bulk, but not to 

 dryness. Wash the colored silk with water and dry by pressing 

 between filter paper and then allowing to stand in the air for a 

 time. 



For red-litmus-silk, treat with the weakest possible acetic acid 

 and dry by pressing between filters just before using. 



For blue-litmus-silk, treat with the weakest possible sodium 

 hydroxide and dry between filters. 



Turmeric-Linen-Fibers. 3 Boil commercial turmeric root 

 with twice its weight of alcohol until all the coloring matter is 

 extracted. Filter and evaporate to dryness on the water bath. 

 Dissolve the residue in an amount of dilute alcohol (to which a 

 drop of sodium hydroxide has been added) equal to about half 

 the weight of turmeric root taken. Place the fibers, previously 

 boiled in water, in this solution and evaporate almost to dryness 

 upon the water bath. Wash once with water, press between 

 filter paper and treat with water acidulated with sulphuric acid. 

 Press between filters, wash with water and dry. 



Zinc-Sulphide-Fibers. 4 Soak guncotton in a strong solution 

 of zinc sulphate, decant the solution and pour upon the wet 

 cotton a dilute solution of sodium sulphide. After standing a 

 short time, decant, wash the fibers with water and dry them for 

 use. 



Congo-Red-Silk. Prepare a strong solution of congo red, 

 make it very slightly alkaline and heat it to boiling; while it is 

 still hot stir in the coarse raw silk fibers and allow the prepara- 

 tion to stand for a short time. Remove the fibers, wash very 

 thoroughly with distilled water, press between filter paper and 



1 Emich, Monats., 22 (1901), 670. 



2 Wartha, Zeit. anal. Chem., 15 (1876), 322. 



3 Donau, Ann., 361 (1907), 426. 



4 Donau, Ann., 361 (1907), 432. 



