4O MICRO-CHEMICAL REAGENTS. 



SULPHO-CYANATE OF POTASSIUM. 



An alcoholic solution is employed, sometimes in 

 combination with hydrochloric acid, for the detec- 

 tion of iron in the cell-wall. (See the second sec- 

 tion, Iron.) 



POTASSIUM BICHROMATE. 



An aqueous solution is used for the detection of 

 tannic acid. 1 Masses of tissue of considerable size 

 are left in the reagent for some time. Cells which 

 contain tannin assume a reddish-brown color. The 

 iron-reactions, however, are preferable. 



It is also used for hardening resin masses. 



NITRATE OF SILVER. 



A very dilute alkaline solution in water has been 

 employed for testing the living condition of proto- 

 plasmic bodies which, in this condition, contain 

 aldehyde. According to Loew and Bokorny, 2 the 

 discoverers of this reaction, the reagent is pre- 

 pared as follows : i. A one per cent, solution of 

 nitrate of silver is made in distilled water. 2. A 

 mixture of 13 cc. potassic hydrate solution (s. g. 

 I -333)> IO cc - ammonia (s. g. .964), and 77 cc. dis- 



1 Dippel : Das Mikroskop, I., p. 280. Sanio : Bot. Zeitung, 1863, p. 

 1 7. Hanstein : Organe der Harz und Schleimabsonderung. Bot. Zeitung, 

 1868, p. 702. Nageli: Das Mikroskop, 1877, p. 475. Weiss: Allgem. 

 Bot., I., p. 187, note. 



2 Pflugers Archiv., 1881, XXV. ; Jahrb. wiss. Bot., 1882. 



